Pumps, Fans, Blowers, And Compressors 62536b

ChE 413 – Momentum Transfer

TRANSPORTATION OF FLUIDS: Fluid-moving Machineries (Pumps, Fans, Blowers, and Compressors) Submitted by: GARCIA, Ann Clarisse M. MALIWAT, Kris Marielle H. SISON, Bren YUMUL, Maria Lara Angela B.

Submitted to: Engr. Denvert C. Pangayao September 9, 2017

TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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TABLE OF CONTENTS Transportation of Fluids ........................................................................................................ 3 Fluid-Moving Machineries ............................................................................................... 4 Pumps ................................................................................................................................... 4 Positive-displacement Pumps ............................................................................ 10 Centrifugal Pumps .................................................................................................. 29 Fans, Blowers, and Compressors ............................................................................ 46 Fans ............................................................................................................................... 46 Blowers ........................................................................................................................ 54 Compressors ............................................................................................................. 58 References ............................................................................................................................... 66


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TRANSPORTATION OF FLUIDS In the industry, transportation of fluids from one process to equipment to another is usually employed. The primary means of transfer of energy to the fluid that causes flow are: 

Transfer of momentum- Deceleration of one fluid (motivating fluid) in order to transfer its momentum to a second fluid (pumped fluid) is a principle commonly used in the handling of corrosive materials, in pumping from inaccessible depths, or for evacuation.

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Mechanical Impulse - principles of force multiplied by time. This principle is usually combined with one of the other means of imparting motion, usually with the use of pumps.

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Gravity - the force of attraction by which a certain body tend to fall toward the center of the earth

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Displacement - Discharge of a fluid from a vessel by partially or completely displacing its internal volume with a second fluid or by mechanical means is the principle upon which a great many fluid transport devices operate.

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Electromagnetic force- When the fluid is an electrical conductor, as is the case with molten metals; it is possible to impress an electromagnetic field around the fluid conduit in such a way that a driving force that will cause flow is created. Such pumps have been developed for the handling of heat-transfer liquids, especially for nuclear reactors.

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Centrifugal force- applied by means of the centrifugal pump or compressor. Though the physical appearance of the many types of centrifugal pumps varies greatly, the basic function of each is the same, i.e., to produce kinetic energy by the action of centrifugal force and then to convert this energy into pressure by efficiently reducing the velocity of the flowing fluid.

In order to transport fluids, mechanical device such pump, fan, blower, or compressor – which increases the fluid energy may be used. Pumps are used for transportation (handling) of liquids; fan, blowers, and compressors are used for transportation of gases.


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PUMPS When a fluid has to be "moved" in a system, pumps are used. The pump is a machine which has the function of increasing the total energy of a liquid; this means that the pump transfers energy to the fluid that it receives from the driving motor. Fluids to be transported may be of low viscosity or highly viscous or it may be corrosive or not therefore, all these factors influence the choice of pump. Pumps may be classified on the basis of the application they serve. All pumps may be divided into two major categories: (1) dynamic, in which energy is continuously added to increase the fluid velocities within the machine, and (2) displacement, in which the energy is periodically added by application of force.

Figure 1. Classification of Pumps According to its Application

General Application of Pumps: 

To pump a liquid from lower pressure area to a high pressure area.

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To increase Flow rate.

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To move liquid from lower elevation to higher elevation.


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IMPULSE PUMPS Impulse pumps use pressure created by gas (usually air). In some impulse pumps the gas trapped in the liquid (usually water), is released and accumulated somewhere in the pump, creating a pressure which can push part of the liquid upwards. Hydraulic ram pumps A hydraulic ram is a water pump powered by hydropower. It functions as a hydraulic transformer that takes in water at one "hydraulic head" (pressure) and flow-rate, and outputs water at a higher hydraulic-head and lower flow-rate. The device utilizes the water hammer effect to develop pressure that allows a portion of the input water that powers the pump to be lifted to a point higher than where the water originally started. The hydraulic ram is sometimes used in remote areas, where there is both a source of low-head hydropower, and a need for pumping water to a destination higher in elevation than the source. In this situation, the ram is often useful, since it requires no outside source of power other than the kinetic energy of flowing water.

Figure 2. Parts of Hydraulic Pump

1. Drive Pipe - Normally the length of the drive pipe should be around three to seven times the supply head. Ideally the drive pipe should have a length of at least 100 times its own diameter. The drive pipe must generally be straight; any bends will not only cause losses of efficiency, but will result in strong fluctuating sideways forces on the pipe which can cause it to break loose. Burying prevents tampering by animals or people. 2. Excess Water Valve - The cycling of the hydraulic ram is timed by the characteristic of the waste valve. Normally it can be weighted or pre-tensioned by an adjustable spring, and an adjustable screwed stop is generally provided which TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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will allow the maximum opening to be varied. The efficiency, which dictates how much water will be delivered from a given drive flow, is critically influenced by the valve setting. This is because if the waste valve stays open too long, a smaller proportion of the throughput water is pumped, so the efficiency is reduced, but if it closes too readily, then the pressure will not build up for long enough in the hydraulic ram body, so again less water will be delivered. There is often an adjustable bolt which limits the opening of the valve to a predetermined amount which allows the device to be turned to optimize its performance. A skilled installer should be able to adjust the waste valve on site to obtain optimum performance. 3. Delivery Pipe - The delivery pipe can be made from any material capable of carrying the pressure of water leading to the delivery tank. In all except very high head applications, plastic pipe can be considered; with high heads, the lower end of the delivery line might be better as steel pipe. The diameter of the delivery line needs to allow for avoiding excessive pipe friction in relation to the flow rates envisaged and the distance the water is to be conveyed. It is recommended that a hand-valve or check-valve (non-return valve) should be fitted in the delivery line near the outlet from the hydraulic ram, so that the delivery line does not have to be drained if the hydraulic ram is stopped for adjustment or any other reason. This will also minimize any back flow past the delivery valve in the air chamber and improve efficiency. 4. Impulse Valve - There are a number of types impulse valves that may be used. The weighted-bolt-impulse valve is durable, easy to maintain, and the principles are easy enough for anyone to understand. Less weight means there will be a quicker stroke and less water pumped. More weight means slower strokes and more water pumped. 5. Delivery Valve - Also known as a check valve. Only allows fluid to travel one direction. Types of check valves include: ball, swinging, diaphragm, lift-check. 6. Pressure Vessel - A large surge in pressure from the water compresses the air inside the pressure vessel. This surge in pressure is known as the known as the water hammer effect.


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Working Principle Initially the impulse valve (or waste valve since it is the non-pumped water exit) will be open under gravity (or in some designs it is held open by a light spring). The water will then flow down the drive pipe (through a strainer) from the water source. As the flow accelerates, the hydraulic pressure under the impulse valve and the static pressure in the body of the hydram will increase until the resulting forces overcome the weight of the impulse valve and start to close it. As soon as the valve aperture decreases, the water pressure in the hydram body builds up rapidly and slams the impulse valve shut. The moving column of water in the drive pipe is no longer able to exit via the impulse valve so its velocity must suddenly decrease; this continues to cause a considerable rise of pressure which forces open the delivery valve to the air-chamber. Once the pressure exceeds the static delivery head, water will be forced up the delivery pipe. Air trapped in the air chamber is simultaneously compressed to a pressure exceeding the delivery pressure. Eventually the column of water in the drive pipe comes to a halt and the static pressure in the casing then falls to near the supply head pressure. The delivery valve will then close, when the pressure in the air chamber exceeds that in the casing. Water will continue to be delivered after the delivery valve has closed until the compressed air in the air chamber has expanded to a pressure equal to the delivery head. A check valve is included in the delivery pipe to prevent return flow. When the delivery valve closes, the reduced pressure in the hydram body will allow the impulse valve to drop under its own weight, thereby letting the cycle start all over again. Most hydrams operate at 15-200 cycles a minute (Brown 1951).

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Advantages No Electricity or External Power Source Continual Operation Easy to Maintain Long Life Reliable

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Disadvantages Only suitable for certain sites Large amount of excess water runoff (though normally this would be piped or ducted back to the source) Typically, low exit flow rates per pump May need to address sedimentation issues


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Airlift Pumps

Figure 3. Airlift Pump

From the name itself, it is a pump for inducing flow of a liquid through the introduction of less dense immiscible fluid – compressed air. Airlift has low suction and moderate discharge of liquid and entrained solids. The pump injects compressed air at the bottom of the discharge pipe which is immersed in the liquid. The compressed air mixes with the liquid causing the air-water mixture to be less dense than the rest of the liquid around it and therefore is displaced upwards through the discharge pipe by the surrounding liquid of higher density. Working Principle A rising main, which is submerged in a well so that more of it is below the water level than above it, has compressed air blown into it at its lowest point. The compressed air produces a froth of air and water, which has a lower density than water and consequently rises to the surface. The compressed air is usually produced by an engine driven air compressor, but windmill powered air compressors are also used. The principle of it is that an air/water froth, having as little as half the density of water, will TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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rise to a height above the water level in the well approximately equal to the immersed depth of the rising main. The greater the ratio of the submergence of the rising main to the static head, the more froth will be discharged for a given supply of air and hence the more efficient an air lift pump will be. Therefore, when used in a borehole, the borehole needs to be drilled to a depth more than twice the depth of the static water level to low adequate submergence. 

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Advantages The pump is very reliable. The very simple principle is a clear advantage. Only air with a higher pressure than the liquid is required. The liquid is not in with any mechanical elements. Therefore, neither the pump can be abraded (which is important for sandwater wells), nor the contents in the pipe (which is important for archeological research in the sea). Act as a water aerator and can in some configurations lift stagnant bottom water to the surface (of water tanks). Since there are no restrictive pump parts, solids up to 70% of the pipe diameter can be reliably pumped.

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Disadvantages Conventional airlift pumps have a flow rate that is very limited. The pump is either on or off. It is very difficult to get a wide range of proportional flow control by varying the volume of compressed air. The suction is limited. This pumping system is suitable only if the head is relatively low. If you want to obtain a high head, you have to choose a conventional pumping system. Because of the principle, a lot of air remains in the liquid. In certain case, this can be problematic, as, for example, in a waste water treatment plant, before an anaerobic basin.


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POSITIVE DISPLACEMENT PUMPS

Positive displacement pump is one in which a definite volume of liquid is trapped in a chamber, which is filled from the inlet and emptied at a higher pressure through the discharge. This volume is constant regardless of the resistance to flow offered by the system the pump is in. These pumps are the second most popular type of pump, next to centrifugal pumps. However, positive displacement pumps come in a wider variety such as gear, lobe, peristaltic, screw, and many other types of pumps. These are generally used for specialist applications such as for pumping viscous liquids or liquids that contain suspended or fragile solids. These pumps are typically not capable of such a high flow rate as say, a centrifugal pump, but they are capable of producing much higher pressures.  PRINCIPLE OF OPERATION

A positive displacement pump makes a fluid move by trapping a fixed amount of the fluid and forcing or displacing that trapped volume into a discharge pipe or discharge system. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. Thus, a constant flow is maintained by the pump and the volume remains constant through each cycle of pump operation. Positive Displacement pumps do not use impellers, but rely on rotating or reciprocating parts to directly push the liquid in an enclosed cavity, until enough pressure is built up to move the liquid into the discharge system. The pump does not rely on raising the velocity of the fluid as the centrifugal pump does by moving the liquid through the impeller. Consequently, the fluid velocity inside a positive displacement pump is much lower than that of a centrifugal pump. This is often a TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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desirable feature for certain applications, such as when needing to pump a media containing fragile solids.

Figure A.1. PV Diagram of Positive Displacement Pumps The figure above is a representation of the pump process of a positive displacement pump in the pressure, volume (P,V) diagram. During suction (1), the volume increases at low pressure. Pushing out the fluid (2) occurs as the volume reduces at high pressure. The enclosed area corresponds to the work done on the fluid.  PUMP CHARACTERISTICS In theory, positive displacement pumps can produce the same flow at a given speed (RPM) no matter what the discharge pressure. Therefore, positive displacement pumps can be regarded as constant flow devices. However, a slight increase in internal leakage as the pressure increases can prevent a truly constant flow rate. 1. Flow rate versus pressure. By looking at the performance chart to the right you can see just how different PD and centrifugal pumps are. The centrifugal has varying flow depending on pressure or head, whereas the PD pump has more or less constant flow regardless of pressure.


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2. Flow rate versus viscosity Another major difference between the pump types is the effect viscosity has on the capacity of the pump. You will notice in the flow rate how the centrifugal pump loses flow as the viscosity goes up but the PD pump’s flow actually increases. This is because the higher viscosity liquids fill the clearances of the pump causing a higher volumetric efficiency. , this chart shows effect of viscosity on the pump flow; when there is a viscosity change there is also greater lin loss in the system. This means you will also have to calculate the change in pump flow from the first chart for this pressure change.

3. Efficiency versus pressure The pumps behave very differently when considering mechanical efficiency as well. Looking at the efficiency chart to the right you can see the impact of pressure changes on the pump’s efficiency. Changes in pressure have little effect on the PD pump but a dramatic one on the centrifugal. 4. Efficiency versus viscosity Viscosity also plays an important role in mechanical efficiency. Because the centrifugal pump operates at motor speed, efficiency goes down as viscosity increases due to increased frictional losses within the pump. Efficiency often increases in a PD pump with increasing viscosity. Note how rapidly efficiency drops off for the centrifugal pump as viscosity increases.  PURPOSE


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Positive displacement pumps transfer fluids from one point to another by first suctioning the fluid in the suction valve and then pumping it out in the discharge valve to achieve the following:

1. Positive displacement pumps are used to transport fluids from low elevation to a higher elevation.

2. Positive displacement pumps are used to transport fluids from low pressure to high pressure areas.

3. Positive displacement pumps are used to increase the flow rate of the fluid that is being pumped.

 TYPICAL SPECIFICATION OF POSITIVE DISPLACEMENT PUMPS Positive displacement pumps are generally available to deliver performance in accordance with the following ranges:    

Flow rates range between 0.4 to 55,000 lpm Total head (pressure) ranges between 0.7 and 6800 Bar Horsepower ranges between 0.5 and 4,900 hp Viscosity limits vary with pump type.


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COMPONENTS OF A POSITIVE DISPLACEMENT PUMP

Figure A.2. An Example of a Positive Displacement Pump The components of a piston pump with their description are as follows: 1. Crank. Crank is a circular disk attached to the motor and used to transfer the rotation motion of the motor to the piston. 2. Connecting rod. Connecting rod is the long solid rod. It provides connection between the crank and the piston. It also converts the rotation of the crank into the linear motion of the piston. 3. Piston. Piston is the solid cylinder like part of the pump which moves linearly in the hollow cylinder of the pump. It is the main component behind the suction and deliverance of the liquid. 4. Pump Cylinder. It is a hollow cylinder in which the piston moves. Suction and deliverance take place within it. Suction and delivery pipe, and valves are attached to one end of the cylinder, while the piston comes and goes back from the other end.


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5. Suction pipe. The pipe which takes the liquid from the source and delivers it to the cylinder of the pump is called the suction pump. 6. Suction valve. It is a one-way valve placed between the suction pipe and cylinder of the pump. It is opened when the suction take place and close when delivery of the fluid is taking place. 7. Delivery pipe. The pipe which takes the liquid from the cylinder of the pump and delivers it to the tank is called a delivery pipe. 8. Delivery valve. It is a one-way valve placed at the point of attachment of delivery pipe and the pump cylinder. It is opened when the delivery of the fluid is taking place and closed when suction of fluid is taking place. In application, a positive displacement pump must not be allowed to operate against a closed valve on the discharge side of the pump, because it has no shutoff head like a centrifugal pump. With the pump operating against a closed discharge valve, it will continue to produce flow, and the pressure in the discharge line will build up until the pipeline can either fracture or the pump can become severely damaged, or both. To prevent this, a relief or safety valve on the discharge side of the positive displacement pump is therefore often necessary. This relief valve can be positioned either internally or externally to the pump. The pump manufacturer normally has the option to supply internal relief or safety valves. An internal valve is usually only used as a safety precaution, but an external relief valve in the discharge line, with a return line back to the suction line or supply tank will provide increased safety. TYPES OF POSITIVE DISPLACEMENT PUMPS AND THEIR WORKING MECHANISMS Positive displacement pumps are classified into two main classes based on their design and operation: rotary pumps and reciprocating pumps. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Figure A.3. Types of Positive Displacement Pump I.

RECIPROCATING PUMPS Reciprocating pumps move liquid by means of a constant back-and-forth motion of a piston, plunger, or diaphragm within a fixed volume or cylinder. Reciprocating pumps can handle viscous and abrasive fluids. They are low-speed machines when compared with centrifugal and rotary pumps. They offer higher efficiencies, generally 85 to 94%, thus they require less horsepower. Reciprocating pumps are best suited for high-pressure and low-volume applications. They frequently require pulsation dampeners because of the pulsating nature of the flow. They have higher installed costs (usually offset by higher efficiencies) and higher maintenance costs than centrifugal or rotary pumps. 1. Piston Pump The oldest and best known positive displacement pump is the piston pump. It uses a piston to force liquid from the inlet side to the outlet side of the pump. A tight-fitting piston in a closed cylinder acts as a displacer designed to push liquid from the cylinder. As the piston moves upwards it will reduce the pressure in the pump body. This causes the pressure in the suction line to open the suction valve and permit the liquid to flow into the pump. In the same way, the higher


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pressure in the discharge line keeps the discharge valve closed. This is called the “suction cycle.” When the piston moves downwards, it increases the pressure in the body, closing the suction valve and opening the discharge valve to force the liquid out of the pump. This is called the “discharge cycle.” The movement of the piston inside the pump body creates pressure inside the pump. Because of this, you must ensure that a piston pump is never operated against a closed discharge valve. All discharge valves must be open before the pump is started to prevent a quick increase of pressure that could damage the pump or the system.

Figure A.4. Piston Pump

Pump Characteristics:     

Piston pumps are capable of almost any pressure, and of large flow capacity. They have the ability to develop high pressures in a single stage. Piston pumps are expensive in large sizes. Easily controlled by stroke adjustment or variable speed. One disadvantage of this type of pump is the necessity of slow speed operation.

2. Plunger Pump A loose-fitting plunger in a closed cylinder acts as a displacer designed to push liquid from the cylinder. Plunger does not touch the TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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cylinder walls. This pump displaces only part of the liquid in the cylinder, and reciprocates inside a stationary packing to prevent leakage between the plunger and the cylinder. As the piston moves upwards it will reduce the pressure in the pump body. This causes the pressure in the suction line to open the suction valve and permit the liquid to flow into the pump. In the same way, the higher pressure in the discharge line keeps the discharge valve closed. This is called the “suction cycle.” When the piston moves downwards, it increases the pressure in the body, closing the suction valve and opening the discharge valve to force the liquid out of the pump. This is called the “discharge cycle.” The movement of the piston inside the pump body creates pressure inside the pump. Because of this, you must ensure that a piston pump is never operated against a closed discharge valve. All discharge valves must be open before the pump is started to prevent a quick increase of pressure that could damage the pump or the system.

Figure A.5. Plunger Pump

Pump Characteristics:    

Plunger pumps are capable of almost any pressure, and of large flow capacity. They have the ability to develop high pressures in a single stage. Plunger pumps are expensive in large sizes. Easily controlled by stroke adjustment or variable speed.


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One disadvantage of this type of pump is the necessity of slow speed operation.

3. Diaphragm Pump In a diaphragm pump, fluid is transferred by the pressure of a diaphragm that flexes to form a cavity that is filled by the liquid. The plunger displaces the hydraulic fluid and the hydraulic fluid moves the diaphragm. The pump will function when a diaphragm is forced into reciprocating motion by mechanical linkage, compressed air, or fluid from a pulsating, external source. The pump construction eliminates any between the liquid being pumped and the source of energy. This eliminates the possibility of leakage, which is important when handling toxic or very expensive liquids.

Figure A.6. Diaphragm Pump

Pump Characteristics:    

Diaphragm pumps transfer virtually any liquid. Designs can handle high temperatures. This pump is adjustable in capacity and discharge pressure by regulating the movement of the diaphragm. It can be flexed by either an air supply or a reciprocating plunger.


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 

II.

This pump is used for pumping chemicals, glue, ink, solvents, fats, grease, and dirty water. This type of reciprocating pump is limited to low flow and head application due to the design of the flexible diaphragm.

ROTARY PUMPS Positive displacement rotary pumps are pumps that move fluid using the principles of rotation. The vacuum created by the rotation of the pump captures and draws in the liquid. Rotary pumps are very efficient because they naturally remove air from the lines, eliminating the need to bleed the air from the lines manually. Positive displacement rotary pumps also have their weaknesses. Because of the nature of the pump, the clearance between the rotating pump and the outer edge must be very close, requiring that the pumps rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the fluids will cause erosion. Rotary pumps that experience such erosion eventually show signs of enlarged clearances, which allow liquid to slip through and detract from the efficiency of the pump.

1. Rotary Gear Pump In a gear pump, the liquid is trapped by the opening between the gear teeth of two identical gears and the chasing of the pump on the suction side. On the pressure side the fluid is squeezed out when the teeth of the two gears are rotated against each other.  External Gear The external rotary gear pump is a positive displacement pump where the meshing of the gears produces a partial vacuum to draw the liquid into the pump. The liquid is carried between the gear teeth and the casing to the opposite side of the pump. The meshing of the gears forces the liquid into the outlet line.


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Figure A.7. External Gear Pump The direction of pump rotation determines which of the nozzles will be the inlet and the outlet. By reversing rotation, the function of the nozzles will be reversed and the pump will be able to pump ‘backwards’. Where one gear is driven by the other, the driven gear usually runs in sleeve type bearings. The bearings and shaft journal are located in the pump casing and surrounded by the pumped fluid. Consequently, these bearings and gears are dependent on the lubricating qualities of the pumped fluid.

 Internal Gear The internal-gear pump is similar in principle to the external gear except the drive shaft turns a ring gear with internal teeth. The external gear tooth rotates on an offset center and meshes with the drive gear through only a segmental arc of rotation. A fixed crescentshaped filter occupies the space between internal- and externalgear-tooth tips opposite the mesh point.


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Figure A.8. Internal Gear Pump As the gear teeth disengage at the input port, fluid enters and is trapped in the tooth space of each gear and is carried to the discharge port. The meshing of the two gears and the elimination of the tooth space forces fluid from the pump. The absence of metallic between the surfaces of the rotors and the casing, means that wear on these parts is insignificant. The only wear that occurs is due to friction with the pumped fluid. 2. Lobe Pump Lobe pumps operate in the same manner as gear pumps except the rotating elements have two, three, or four lobes instead of gear teeth. Lobes cannot drive each other, so timing gears are used. The lobes never come into with each other so the pump can be allowed to run dry. Lobes are used where product integrity must be maintained and in applications in which liquids are shear sensitive. The large volume created between the casing and lobes allows many products to be pumped without damaging the product itself. A major advantage is that there is no metal-to-metal between the lobes, thus the possibility of traces of iron, steel, or other pump-construction materials ending up in the product because of wear is greatly reduced. On the other hand, they are more expensive than gear or vane pumps and are difficult to repair and maintain.


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Figure A.9. Lobe Pump 3. Vane Pump A set of vanes is mounted in a rotor in which the vanes slide in and out of the rotor. The rotor is mounted off center in the casing. As the vanes rotate past the suction port, they slide out of the rotor while maintaining constant with the casing. Springs or sealer rings help hold the vanes against the casing, thus the vanes make a close seal, or fit, against the casing wall. Trapped fluid is forced from the suction port to the discharge port. The sliding-vane design is capable of delivering medium capacity and head. They deliver a constant flow rate for a set rotor speed. They work well with low-viscosity fluids and are somewhat self-compensating for wear. They are not suitable for use with highly viscous fluids (thicker fluids interfere with the sliding action of the vanes). A large wear area results from the friction fit between the vanes and the cylinder.

Figure A.10. Vane Pump TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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4. Peristaltic Pump A peristaltic pump is a type of positive displacement pump used for pumping a variety of fluids. The fluid is contained within a flexible tube fitted inside a circular pump casing (though linear peristaltic pumps have been made). A rotor with a number of "rollers", "shoes" or "wipers" attached to the external circumference compresses the flexible tube. As the rotor turns, the part of the tube under compression closes (or "occludes") thus forcing the fluid to be pumped to move through the tube. Additionally, as the tube opens to its natural state after the ing of the cam ("restitution") fluid flow is induced to the pump. This process is called peristalsis and is used in many biological systems such as the gastrointestinal tract.

Figure A.11. Peristaltic Pump 5. Screw Pump Screw pumps are a special type of rotary positive displacement pump in which the flow through the pumping elements is truly axial. The liquid is carried between screw threads on two or more rotors and is displaced axially as the screws rotate and mesh. The meshing of the threads on the rotors and the close fit of the surrounding housing create one or more sets of moving seals in series between pump inlet and outlet. These sets of seals act as a labyrinth and provide the screw pump with its positive pressure capability. The successive sets of seals for fully enclosed cavities move continuously from inlet to outlet. These cavities trap liquid at the inlet and carry it along to the outlet, providing a smooth flow with minimal pulsations. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Figure A.12. Screw Pump 6. Progressive Cavity As the rotor rotates inside the stator, two cavities form at the suction end of the stator. One cavity closing as the other opens and the cavities progress from one end of the stator to the other. The result is a flow with relatively little pulsation. Since the longest path through the elements is a spiral, and not far from a straight line, the shear rates will also be low in comparison to those in other types of pumps. The compressive fit between the rotor and stator creates seal lines where the two components . The seal lines keep the cavities separated as the cavities move through the pump with each rotation of the rotor. The elastomeric stator and stainless steel rotor allow the pump to handle large solid particles in suspension and a certain percentage of abrasives. The manner in which the rotor turns within the stator complicates the mechanical design of progressive cavity pumps. As the rotor turns in the stator, the centerline of the rotor orbits about the centerline of the stator. This eccentric motion means the pump must be fitted with universal ts to transmit power from the concentric rotation of the drive shaft to the eccentrically rotating rotor. These ts must transmit torsional and thrust loads. Depending on the size of the pump, designs of this drive mechanism range from simple ball-and-pin mechanisms to heavy-duty sealed gear couplings. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Figure A.13. Progressive Cavity Pump COMMON PUMPING PROBLEMS Common problems that occur during operation of positive displacement pumps are presented below. Six common problems and possible reasons for each one are addressed as well. 1. 2. 3. 4. 5. 6.

The pump does not deliver any liquid The pump delivers less liquid than its rated capacity The prime is lost during operation of the pump The pump is noisy The pump wears more rapidly than should be expected, and The pump takes too much power

PROBLEMS No liquid delivered

Delivers less than rated capacity

sLoss of prime while pump is operating Pump is noisy

POSSIBLE CAUSES Pump is not primed. Suction line clogged. Relief valve jammed open. Pump rotates in wrong direction. Suction or discharge valve is closed. Air leak in suction line or pump seal. Relief valve wrongly set. Suction or discharge valve partially closed. Liquid level falls below the suction line. Liquid vaporizes in suction line. Cavitation, misalignment, or foreign material inside pump.


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Rapid pump wear Pump takes too much power

Grit or abrasive material in liquid. Speed is too high. Liquid is more viscous than specified. Discharge line too small.

PRIMARY ADVANTAGES OF POSITIVE DISPLACEMENT PUMPS 1. In general, positive displacement pumps are ideal for applications where a constant flow is needed. 2. They create medium to high pressure and are often an excellent way to pump oils and other viscous fluids. 3. Positive displacement pumps are also extremely useful for applications requiring a combination of low flow and high pressure. For example, to move fluids containing suspended or fragile solids. 4. This type of pump is suitable for high pressures and only one stage is required. 5. Positive displacement pumps have a very good suction capacity, even if the fluid includes gas. 6. The flow rate can be adjusted very precisely and reproducibly via stroke and stroke rate. 7. Cyclical delivery is possible and it is well suited for low drive speeds.

LIMITATIONS OF POSITIVE DISPLACEMENT PUMPS 1. Principle of operation does not include a pressure restriction, therefore safety or pressure relief valves are necessary in positive displacement pumps. 2. Vibration- free operation is only possible with complex mass balancing. 3. Reciprocating positive displacement pumps are less suitable for high flow rates. 4. In reciprocating positive displacement pumps, pulsating flow is necessary, as is a pulsation dampener. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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5. In some more complicated designs, construction of valves are fault-prone 6. Larger number of wear parts are present in positive displacement pumps than centrifugal pumps.

APPLICATIONS OF POSITIVE DISPLACEMENT PUMPS A wide variety of industries benefit from a positive displacement pump, especially industries concerned with highly viscous fluids, shear sensitive fluids, abrasive fluids, and fluids with solid particles. Food and Beverage Industry, Personal Care Industry, Cosmetics Industry, Dairy or Meat Processing Industry, Pharmaceutical Industry, and Wastewater Treatment Facilities are some of the industries where positive displacement pumps are of great importance.

Kinetic Pumps

– Add energy directly through a rotating part in the form of velocity, and converts the velocity to pressure. • Centrifugal Pumps • Regenerative Pumps: Unique pump where the impeller is the only moving part. It is used when high head and low flows are required.

• Special Effects Pumps: Miscellaneous pumps.


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CENTRIFUGAL PUMPS

A centrifugal pump is one of the simplest pieces of equipment in any process plant. It is the most popular pump used and is the chief pump type in the class of kinetic pumps. It is a mechanical device used to transport fluids by the conversion of energy of a prime mover (an electric motor or turbine) first into velocity or kinetic energy and then into pressure energy of a fluid (commonly air, water, sewage, petroleum, and petrochemicals)that is being pumped. . The principle is simple, well-described and thoroughly tested, and the pump is robust, effective and relatively inexpensive to produce. The energy changes occur by virtue of two main parts of the pump, the impeller and the volute or diff. The impeller is the rotating part that converts driver energy TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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into the kinetic energy. The volute or diff is the stationary part that converts the kinetic energy into pressure energy.

History According to Reti, the Brazilian soldier and historian of science, the first machine that could be characterized as a centrifugal pump was a mud lifting machine which appeared as early as 1475 in a treatise by the Italian Renaissance engineer sco di Giorgio Martini. True centrifugal pumps were not developed until the late 17th century, when Denis Papin made one with straight vanes. The curved vane was introduced by British inventor John Appold in 1851. The centrifugal pump was developed in Europe in the late 1600's and was seen in the United States in the early 1800's. Its wide spread use, however, has occurred only in the last seventy-five years. Prior to that time, the vast majority of pumping applications involved positive displacement pumps. The increased popularity of centrifugal pumps is due largely to the comparatively recent development of high speed electric motors, steam turbines, and internal combustion engines. The centrifugal pump is a relatively high speed machine and the development of high speed drivers has made possible the development of compact, efficient pumps.Since the 1940's, the centrifugal pump has become the pump of choice for many applications. Research and development has resulted in both improved performance and new materials of construction that have greatly expanded it's field of applicability. It is not uncommon today to findd efficiencies of 93%+ for large pumps and better than 50% for small fractional horsepower units. Modern centrifugal pumps have been built to meet conditions far beyond what was thought possible fifty to sixty years ago. Pumps capable of delivering over 1,000,000 gallons per minute at heads of more than 300 feet are common in the nuclear power industry. And, boiler feed pumps have been developed that deliver 300 gallons per minute at more than 1800 feet of head. (Evans)

General Components of Centrifugal Pumps A centrifugal pump has two main components: I. A rotating component comprised of an impeller and a shaft II. A stationary component comprised of a casing, casing cover, and bearings.


30

The general components, both stationary and rotary, are depicted in Figure C.01. The main components are discussed in brief below. Figure C.02 shows these parts on a photograph of a pump in the field.

Stationary Components Casing Casings are generally of two types: volute and circular. The impellers are fitted inside the casings. 1. Volute casings build a higher head; circular casings are used for low head and high capacity.


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o A volute is a curved funnel increasing in area to the discharge port as shown in Figure C.03. As the area of the cross-section increases, the volute reduces the speed of the liquid and increases the pressure of the liquid.

o One of the main purposes of a volute casing is to help balance the hydraulic pressure on the shaft of the pump. However, this occurs best at the manufacturer's recommended capacity. Running volute-style pumps at a lower capacity than the manufacturer recommends can put lateral stress on the shaft of the pump, increasing wear-and-tear on the seals and bearings, and on the shaft itself. Double-volute casings are used when the radial thrusts become significant at reduced capacities. 2. Circular casing have stationary diffusion vanes surrounding the impeller periphery that convert velocity energy to pressure energy. Conventionally, the diffs are applied to multi-stage pumps. o The casings can be designed either as solid casings or split casings. Solid casing implies a design in which the entire casing including the discharge nozzle is all contained in one casting or fabricated piece. A split casing implies two or more parts are fastened together. When the casing parts are divided by horizontal plane, the casing is described as horizontally split or axially split casing. When the split is in a vertical plane perpendicular to the rotation axis, the casing is described as vertically split or radially split casing. Casing Wear rings act as the seal between the casing and the impeller.


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Suction and Discharge Nozzle The suction and discharge nozzles are part of the casings itself. They commonly have the following configurations. 1. End suction/Top discharge (Figure C.05) - The suction nozzle is located at the end of, and concentric to, the shaft while the discharge nozzle is located at the top of the case perpendicular to the shaft. This pump is always of an overhung type and typically has lower NPSHr because the liquid feeds directly into the impeller eye. 2. Top suction Top discharge nozzle (Figure C.05) -The suction and discharge nozzles are located at the top of the case perpendicular to the shaft. This pump can either be an overhung type or between-bearing type but is always a radially split case pump.

3. Side suction / Side discharge nozzles - The suction and discharge nozzles are located at the sides of the case perpendicular to the shaft. This pump can have either an axially or radially split case type. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Seal Chamber and Stuffing Box Seal chamber and Stuffing box both refer to a chamber, either integral with or separate from the pump case housing that forms the region between the shaft and casing where sealing media are installed. When the sealing is achieved by means of a mechanical seal, the chamber is commonly referred to as a Seal Chamber. When the sealing is achieved by means of packing, the chamber is referred to as a Stuffing Box. Both the seal chamber and the stuffing box have the primary function of protecting the pump against leakage at the point where the shaft es out through the pump pressure casing. When the pressure at the bottom of the chamber is below atmospheric, it prevents air leakage into the pump. When the pressure is above atmospheric, the chambers prevent liquid leakage out of the pump. The seal chambers and stuffing boxes are also provided with cooling or heating arrangement for proper temperature control. Figure C.06 below depicts an externally mounted seal chamber and its parts.

o Gland: The gland is a very important part of the seal chamber or the stuffing box. It gives the packings or the mechanical seal the desired fit on the shaft sleeve. It can be easily adjusted in axial direction. The gland comprises of the seal flush, quench, cooling, drain, and vent connection ports as per the standard codes like API 682. o Throat Bushing: The bottom or inside end of the chamber is provided with a stationary device called throat bushing that forms a restrictive close clearance around the sleeve (or shaft) between the seal and the impeller. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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o Throttle bushing refers to a device that forms a restrictive close clearance around the sleeve (or shaft) at the outboard end of a mechanical seal gland. o Internal circulating device refers to device located in the seal chamber to circulate seal chamber fluid through a cooler or barrier/buffer fluid reservoir. Usually it is referred to as a pumping ring. o Mechanical Seal

Bearing housing The bearing housing encloses the bearings mounted on the shaft. The bearings keep the shaft or rotor in correct alignment with the stationary parts under the action of radial and transverse loads. The bearing house also includes an oil reservoir for lubrication, constant level oiler, jacket for cooling by circulating cooling water

Rotating Components 1. Impeller The impeller is the main rotating part that provides the centrifugal acceleration to the fluid. They are often classified in many ways. o Impellers can be either single- suction or double-suction. A single-suction impeller allows liquid to enter the center of the blades from only one direction. A double-suction impeller allows liquid to enter the center of the impeller blades from both sides simultaneously.

o Impellers can be open, semi-open, or enclosed. The open impeller consists only of blades attached to a hub. The semi-open impeller is constructed with a circular plate (the web) attached to one side of the blades. The enclosed impeller has circular plates attached to both sides of the blades. Enclosed impellers are also referred to as shrouded impellers. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Closed impellers require wear rings and these wear rings present another maintenance problem. Open and semi-open impellers are less likely to clog, but need manual adjustment to the volute or backplate to get the proper impeller setting and prevent internal recirculation. Vortex pump impellers are great for solids and "stringy" materials but they are up to 50% less efficient than conventional designs. The number of impellers determines the number of stages of the pump. A single stage pump has one impeller only and is best for low head service. A two-stage pump has two impellers in series for medium head service. A multi-stage pump has three or more impellers in series for high head service. o Wear rings: Wear ring provides an easily and economically renewable leakage t between the impeller and the casing. Clearance becomes too large the pump efficiency will be lowered causing heat and vibration problems. Most manufacturers require that you disassemble the pump to check the wear ring clearance and replace the rings when this clearance doubles. 2. Shaft The basic purpose of a centrifugal pump shaft is to transmit the torques encountered when starting and during operation while ing the impeller and other rotating parts. It must do this job with a deflection less than the minimum clearance between the rotating and stationary parts. o Shaft Sleeve (Figure C.08): Pump shafts are usually protected from erosion, corrosion, and wear at the seal chambers, leakage ts, internal bearings, and in the waterways by renewable sleeves. Unless otherwise specified, a shaft sleeve of wear, corrosion, and erosion resistant material shall be provided to protect the shaft. The sleeve shall be sealed at one end. The shaft sleeve assembly shall extend beyond the outer face of the seal TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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gland plate. (Leakage between the shaft and the sleeve should not be confused with leakage through the mechanical seal).

o Coupling: Couplings can compensate for axial growth of the shaft and transmit torque to the impeller. Shaft couplings can be broadly classified into two groups: rigid and flexible. Rigid couplings are used in applications where there is absolutely no possibility or room for any misalignment. Flexible shaft couplings are more prone to selection, installation and maintenance errors. Flexible shaft couplings can be divided into two basic groups: elastomeric and non-elastomeric 

Elastomeric couplings use either rubber or polymer elements to achieve flexibility. These elements can either be in shear or in compression. Tire and rubber sleeve designs are elastomer in shear couplings; jaw and pin and bushing designs are elastomer in compression couplings.



Non-elastomeric couplings use metallic elements to obtain flexibility. These can be one of two types: lubricated or nonlubricated. Lubricated designs accommodate misalignment by the sliding action of their components, hence the need for lubrication. The non-lubricated designs accommodate misalignment through flexing. Gear, grid and chain couplings are examples of nonelastomeric, lubricated couplings. Disc and diaphragm couplings are non-elastomeric and non-lubricated.

Working Mechanism The centrifugal pump's function is as simple as its design. It is filled with liquid and the impeller is rotated. Rotation imparts energy to the liquid causing it to exit the impeller's vanes at a greater velocity than it possessed when it entered. This outward flow reduces the pressure at the impeller eye, allowing more liquid to enter. The liquid that exits the impeller is collected in the casing (volute) where its velocity is converted to pressure before it leaves the pump's discharge. Generation of Centrifugal Force TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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The process liquid enters the suction nozzle and then into eye (center) of a revolving device known as an impeller. When the impeller rotates, it spins the liquid sitting in the cavities between the vanes outward and provides centrifugal acceleration. As liquid leaves the eye of the impeller a low-pressure area is created causing more liquid to flow toward the inlet. Because the impeller blades are curved, the fluid is pushed in a tangential and radial direction by the centrifugal force. This force acting inside the pump is the same one that keeps water inside a bucket that is rotating at the end of a string. Figure A.01 below depicts a side cross-section of a centrifugal pump indicating the movement of the liquid.

Conversion of Kinetic Energy to Pressure Energy The key idea is that the energy created by the centrifugal force is kinetic energy. The amount of energy given to the liquid is proportional to the velocity at the edge or vane tip of the impeller. The faster the impeller revolves or the bigger the impeller is, then the higher will be the velocity of the liquid at the vane tip and the greater the energy imparted to the liquid. This kinetic energy of a liquid coming out of an impeller is harnessed by creating a resistance to the flow. The first resistance is created by the pump volute (casing) that catches the liquid and slows it down. In the discharge nozzle, the liquid further decelerates and its velocity is converted to pressure according to Bernoulli’s principle. Therefore, the head (pressure in of height of liquid) developed is approximately equal to the velocity energy at the periphery of the impeller expressed by the following well-known formula:

Pump Stage TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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A pump stage is defined as that portion of a centrifugal pump consisting of one impeller and its associated components. 

Single-stage centrifugal pumps. Most centrifugal pumps are single-stage pumps, containing only one impeller.



Multistage centrifugal pumps. A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. If we need higher pressure at the outlet we can connect impellers in series. If we need a higher flow output we can connect impellers in parallel. All energy added to the fluid comes from the power of the electric or other motor force driving the impeller.

Types of Centrifugal Pumps ACCORDING TO FLOW Centrifugal pumps can be classified based on the manner in which fluid flows through the pump. The manner in which fluid flows through the pump is determined by the design of the pump casing and the impeller. The three types of flow through a centrifugal pump are radial flow, axial flow, and mixed flow 1. Radial Flow Pumps. Often simply referred to as centrifugal pumps. In a radial flow pump, the liquid enters at the center of the impeller and is directed out along the impeller blades in a direction at right angles to the pump shaft (radially).


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2. Axial Flow Pumps. In an axial flow pump, the impeller pushes the liquid in a direction parallel to the pump shaft. The fluid is not accelerated but instead "lifted" by the action of the impeller. Axial flow pumps are sometimes called propeller pumps because they operate essentially the same as the propeller of a boat. Axialflow pumps operate at much lower pressures and higher flow rates than radialflow pumps.

3. Mixed Flow Pumps. Mixed flow pumps borrow characteristics from both radial

flow and axial flow pumps. The fluid experiences both radial acceleration and lift and exits the impeller somewhere between 0 and 90 degrees from the axial direction. As a consequence mixed-flow pumps operate at higher pressures than axial-flow pumps while delivering higher discharges than radial-flow pumps. The exit angle of the flow dictates the pressure head-discharge characteristic in relation to radial and mixed-flow.


40

Characteristics of Centrifugal Pumps Centrifugal pumps are specified by four characteristics: 1. Capacity: This is defined as the quantity of liquid which is discharged from the pump in a given time. Capacity is expressed in 'm3/hr', 'gal/min', ..etc. The capacity of a pump is governed by the 'Head', the 'Speed' and the 'Size' of the pump. 2. Total Head: The total head of a pump is the difference between the pump suction and discharge pressures - expressed in of metres or feet head: Suction Head : This is the vertical distance, in feet or metres, from the centreline of the pump to the level of liquid in the vessel from which the liquid is being pumped. IF THE LIQUID LEVEL IS ABOVE THE PUMP CENTRELINE, THE SUCTION HEAD IS POSITIVE. IF BELOW THE CENTRELINE, THE SUCTION HEAD IS NEGATIVE. Discharge Head: Is the discharge pressure of the pump, expressed in feet or metres of liquid. Total Head: = Discharge head -Suction head 3. Power: This is the energy used by the pump in a given time. Its unit is 'Horsepower' (HP). 1 HP is equivalent to 0.746 kilowatt. (kW). 4. Efficiency:


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This is a percentage measure of the pump's effectiveness in transferring the power used into energy added to the pumped liquid. ● The overall efficiency of a pump is a product of three factors ○ Mechanical Efficiency (Losses in the bearing frame and mechanical seals) ○ Volumetric Efficiency (Losses due to leakage in wear rings and impellers) ○ Hydraulic Efficiency (Losses due to fluid friction within the pump casing) The formula for calculation of efficiency is: Efficiency = (Output power)/(Input power)X 100% ● Centrifugal pumps can have very high efficiencies ○ Medium to Large pumps can be 75% - 90% efficient ○ Small pumps can be 50% to 70% efficient

Advantages and Disadvantages Advantages: ● Simple principle (don’t require valves or moving parts). ● Small in size compared to other pumps with same output. ● Can move at high speeds with minimal maintenance. ● Steady and consistent output ● Can handle large volumes of fluid ● Good for medium to low head ● Good for medium to low viscous fluids

Disadvantages: ● Use rotation instead of suction to move water (very little suction power) ● Close fitting parts can cause maintenance issues as parts wear out ● Pump must be primed before use. Most centrifugal pumps are not self-priming. In other words, the pump casing must be filled with liquid before the pump is started, or the pump will not be able to function. If the pump casing becomes filled with TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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vapors or gases, the pump impeller becomes gas-bound and incapable of pumping. To ensure that a centrifugal pump remains primed and does not become gas-bound, most centrifugal pumps are located below the level of the source from which the pump is to take its suction. The same effect can be gained by supplying liquid to the pump suction under pressure supplied by another pump placed in the suction line. ● Can develop cavitation. ● Not good for high head ● Not good with high viscous fluids

Problems of centrifugal pumps • Cavitation—the NPSH of the system is too low for the selected pump • Wear of the Impeller—can be worsened by suspended solids • Corrosion inside the pump caused by the fluid properties • Overheating due to low flow • Leakage along rotating shaft • Lack of prime—centrifugal pumps must be filled (with the fluid to be pumped) in order to operate • Surge Cavitation Cavitation is a problem condition which may develop while a centrifugal pump is operating. This occurs when a liquid boils inside the pump due to insufficient suction head pressure. Low suction head causes a pressure below that of vaporisation of the liquid, at the eye of the impeller.


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Cavitation is the process of the formation and subsequent collapse of vapor bubbles in a pump. The resultant gas which forms causes the formation and collapse of 'bubbles' within the liquid. This, because gases cannot be pumped together with the liquid, causes violent fluctuations of pressure within the pump casing and is seen on the discharge gauge. These sudden changes in pressure cause vibrations which can result in serious damage to the pump and, of course, cause pumping inefficiency.

There are three indications that a centrifugal pump is cavitating. o Noise o Fluctuating discharge pressure and flow o Fluctuating pump motor current Three effects of pump cavitation are: o Degraded pump performance o Excessive pump vibration o Damage to pump impeller, bearings, wearing rings, and seals To overcome cavitation: o Increase suction pressure if possible. o Decrease liquid temperature if possible. o Throttle back on the discharge valve to decrease flow-rate. o Vent gases off the pump casing.

Net Positive Suction Head (NPSH) To avoid cavitation in centrifugal pumps, the pressure of the fluid at all points within the pump must remain above saturation pressure. The quantity used to determine if the pressure of the liquid being pumped is adequate to avoid cavitation is the net positive suction head (NPSH).The net positive suction head TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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available (NPSHA) is the difference between the pressure at the suction of the pump and the saturation pressure for the liquid being pumped. The net positive suction head required (NPSHR) is the minimum net positive suction head necessary to avoid cavitation. To avoid cavitation, the net positive suction head available must be greater than the net positive suction head required. (Mechanical Science Volume 1)

Applications of Centrifugal Pumps Centrifugal pumps are used in various sectors such as agriculture, power generation plants, municipal, industries, domestic purposes, etc. The pumps are divided in five overall groups: Circulation pumps, pumps for pressure boosting and fluid transport, water supply pumps, industrial pumps and wastewater pumps. Many of the pump types can be used in different applications. 

Circulation pumps are primarily used for circulation of water in closed systems e.g. heating, cooling and air-conditioning systems as well as domestic hot water systems. The water in a domestic hot water system constantly circulates in the pipes. This prevents a long wait for hot water when the tap is opened.



Pumps for pressure boosting are used for increasing the pressure of cold water and as condensate pumps for steam boilers. The pumps are usually designed to handle fluids with small particles such as sand.


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

Water supply pumps can be installed in two ways: They can either be submerged in a well or they can be placed on the ground surface. The conditions in the water supply system make heavy demands on robustness towards ochre, lime and sand.



Industrial pumps can, as the name indicates, be used everywhere in the industry and this in a very broad section of systems which handle many different homogeneous and inhomogeneous fluids. Strict environmental and safety requirements are enforced on pumps which must handle corrosive, toxic or explosive fluids, e.g. that the pump is hermetically closed and corrosion resistant.



Wastewater pumps are used for pumping contaminated water in sewage plants and industrial systems. The pumps are constructed making it possible to pump fluids with a high content of solid particles.


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FANS, BLOWERS, AND COMPRESSORS

FANS  





Any device that produces a current of air by the movement of broad surfaces can be called a fan. Fans fall under the general classification of “turbomachinery” and have a rotating impeller at least partially encased in a stationary housing. Fans are similar in many respects to pumps. Both are turbomachines that transfer energy to a flowing fluid. It is easy to distinguish between fans and pumps: pumps handle liquids; fans handle gases. Broadly speaking, the function of a fan is to propel, displace, or move air or gas.

Fans and blowers provide air for ventilation and industrial process requirements. Fans generate a pressure to move air (or gases) against a resistance caused by ducts, dampers, or other components in a fan system. The fan rotor receives energy from a rotating shaft and transmits it to the air.

Difference between Fans, Blowers, and Compressors TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Fans, blowers and compressors are differentiated by the method used to move the air, and by the system pressure they must operate against. As per American Society of Mechanical Engineers (ASME) the specific ratio – the ratio of the discharge pressure over the suction pressure - is used for defining the fans, blowers and compressors. Equipment Fans Blowers Compressors

Specific Ratio Up to 1.11 1.11 to 1.20 More than 1.20

Pressure Rise (mmWg) 1136 1136 – 2066 -

Parts of a Fan

   

Impeller rotates and transfers energy to the air. (Wheel, rotor, runner, propeller) Blade the working surface. (Vane, paddle) Shroud s the blades (cover disc, inlet plate, backplate, rim, flange) Hub attaches to the fan/motor shaft but may the blades directly (axial) or indirectly through a shroud(centrifugal). (boss, disc)


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   

Housing encloses the impeller and guides the air to and from the impeller. (casing, scroll, , ring, volute) Inlet the opening to the impeller. (eye, suction, suction eye, inlet cone, inlet bell, inlet nozzle) Outlet the opening leaving the fan. (discharge, discharge cone, evasee, diff) Guide Vanes when installed before the impeller are called pre-rotation vanes or inlet guide vanes. If they are adjustable they are called variable inlet vanes or simply VIV’s. When installed after the impeller they are termed straightening vanes or discharge guide vanes.

Classifications of Fans One of the characteristics by which fans are classified is the nature of the flow through the blade ages of the impeller. Axial flow, radial flow, mixed flow, and cross flow are all possible in fan impellers. Certain fan names result from these classifications. Other fan names derive from other characteristics.



Axial-flow Impeller

Propeller fans, tube-axial fans, and vane-axial fans all utilize axial-flow impellers, but their casings differ. Propeller fans may be mounted in a ring or . Tube-axial fans and vane-axial fans both use tubular casings, but for vane-axial fans they are equipped with stationary guide vanes. A great deal of the energy transferred to the air in axial-flow machines is in kinetic form. Some of this kinetic energy can be transformed into pressure energy by straightening the swirl, e.g., with vanes, or by reducing the exit velocity, e.g., with a diff. Propeller fans effect very little transformation and hence have very low pressure-producing capability. Vane-axial fans can be equipped for maximum transformation as well as high transfer of energy and hence have high pressure-producing potential depending on tip speed and blade angles. High hub ratios promote high energy transfer.


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

Radial-flow Impeller

Centrifugal fans and tubular centrifugal fans both utilize radial-flow impellers. Centrifugal fans usually employ a volute or scroll-type casing, the flow entering the casing axially and leaving tangentially. Tubular centrifugals use tubular casings so that the flow both entering and leaving the casing is axial. A considerable portion of the energy transferred to the air in a radial-flow machine is due to centrifugal action; hence the name centrifugal fan. Since centrifugal action varies with blade depth, the pressure-producing capability of radial-flow fans will vary with this factor as well as tip speed and blade angles.



Mixed-flow Impeller

Mixed-flow impellers can be used in either axial or scroll-type casings. They are characterized as mixed flow because both axial and radial flow take place in the blading. Mixed-flow impellers used in axial-flow casings have a hub similar to a pure axial-flow impeller, but the inlet portion of the blading extends down over the face of the hub, thereby giving some radial guidance. Mixed-flow impellers used in scroll-cased fans have blades which give most of the axial guidance in the inlet portion and most of the radial guidance in the discharge portion.



Cross-flow Impeller


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In a cross-flow impeller, the air es through the blading twice, entering more or less tangentially through the tip, ing across the impeller and out the other side. The casings are designed to provide this transverse flow. Cross-flow fans are also known as tangential fans or transverse-flow fans. Pressure-producing potential is low and depends on the formation of a vortex as the air leaves the impeller.

Fan Details and Applications 

Axial Fans

Propeller fans and other axial fans may use blades shaped to airfoil sections or blades of uniform thickness. Blading may be fixed, adjustable at standstill, or variable in operation. Propeller fans have very small hubs. Hub-to-tip diameter ratios ranging from 0.4 to 0.7 are common in vaneaxial fans. The larger the hub, the more important it is to have an inner cylinder approximately the hub size located downstream of the impeller. The guide vanes of a vane-axial fan are located in the annular space between the tubular casing and the inner cylinder. Diffs are generally used between the fan and the discharge ductwork. Type

Propeller

Tube Axial

Vane Axial

Characteristics Low pressure, high flow, low efficiency, peak efficiency close to point of free air delivery (zero static pressure) Medium pressure, high flow, higher efficiency than propeller type, dip in pressure flow curve before peak pressure point High pressure, medium flow, dip in pressure-flow

Typical Applications Air circulation, ventilation, exhaust

HVAC, drying exhaust systems

ovens,

High pressure applications including HVAC systems


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curve, use of guide vanes improves efficiency exhausts 

Centrifugal Fans

Centrifugal fans use various types of blading. Forward-curved blades are shallow and curved so that both the tip and the heel point in the direction of rotation. Radial and radial-tip blades both are radial at the tip, but the latter are curved at the heel to point in the direction of rotation. Backward-curved and backward-inclined blades point in the direction opposite rotation at the tip and in the direction of rotation at the heel. All the above blades are of uniform thickness and are designed for radial flow. Airfoil blades have backward-curved chord lines so that the leading edge of the airfoil is at the heel pointing forward and the trailing edge at the tip pointing backward with respect to rotation. Impellers for all blade shapes are usually shrouded and may have single or double inlets. Blade widths are related to the inlet-to-tip-diameter ratio. Tip angles may vary widely, but heel angles should be set to minimize entrance losses. Scroll casings may be fitted with a streamlined inlet bell, an inlet cone, or simply a collar.

Types Radial

Forward Curved Blades

Characteristics High pressure, medium flow, efficiency close to tube axial fans, power increase continuously Medium pressure, high flow, dip in pressure curve, efficiency higher than radial fans, power rises continuously

Typical Applications Various industrial applications, suitable for dust laden, moist air/ gases Low pressure HVAC, packaged units, suitable for clean and dust laden air/ gases


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Backward Curved Blades

Airfoil Type 

High pressure, high flow, high efficiency, power reduces ass flow increases beyond the point of highest efficiency Same as backward curved type, highest efficiency

HVAC, various industrial applications forced draft fans, etc. Same as backward curved, but for clean air application

Tubular Centrifugals

Tubular centrifugals may be designed for backwardcurve, air-foil or mixed-flow impellers. An inlet bell and discharge guide vanes are required for good performance.



Cross-flow Fans

Cross-flow fans utilize impellers with blading similar to that of a forward-curved centrifugal, but the end shrouds have no inlet holes. Blade-length-to-tip-diameter ratios are limited only by structural considerations.



Power Roof Ventilators

Power roof ventilators may use either axial- or radialflow impellers. The casings will include either a propeller fan mounting ring or a tubular casing to guide the flow for an axial-flow impeller. If a radial-flow impeller is used, an inlet bell is required, but the scroll case may be replaced by the ventilator hood.

All fan types may have direct or indirect drive arrangements. Various standards including arrangement numbers have been adopted by AMCA. Arr. 1 signifies an TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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overhung impeller on a fan shaft with two bearings on a base; Arr. 3 signifies an impeller on a fan shaft between bearings; Arr. 4 is for overhung impeller on a motor shaft; Arr. 7 is Arr.3 with a motor base; Arr. 8 is Arr. 1 with an extended base for motor; Arr. 9 is Arr. 1 with motor mounted on side of unit; Arr. 10 is Arr. 1 with motor mounted inside of base. Rotation is specified as cw or ccw when viewed from the drive side. All fans can be equipped with variable-speed drives, variable inlet vanes, or dampers, but controllablepitch axials do not need speed or vane control.

Working Principle of Centrifugal Fan Air enters a centrifugal fan impeller axially, then es through the impeller radially, the airflow is then collected in the volute casing and discharged at right angles to the inlet flow. As the impeller rotates, the air contained within the blade age is forced outwards due to the centrifugal force. This process happens continually producing a continuous flow through the impeller.

Motion of Air Through an Impeller There are three stages to the pressure development through a centrifugal fan impeller: 1. We know that air is forced through the impeller in the radial direction due to centrifugal effects. As the radius of the impeller increases the magnitude of the centrifugal force on the air increases. This increase in centrifugal force with radius produces a pressure gradient, whereby the static pressure in the blade age increases with radius. 2. Generally the outlet area of the blade age is larger than the inlet area, thus the blade age acts as a diff. The relative velocity reduces as the air flows through the blade age, leading to an additional increase in the static pressure at the impeller outlet. 3. In an open inlet centrifugal fan, air enters the impeller radially. The motion of the blades adds rotational momentum to the flow, increasing the velocity of the flow in the tangential direction. As the air moves radially through the impeller, the absolute velocity of the flow will increase, with the maximum absolute velocity at the impeller outlet. This increase in the absolute velocity of the air leads to an increase in the kinetic energy and dynamic pressure across the impeller. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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BLOWERS Blowers can achieve much higher pressures than fans, as high as 1.20 kg/cm2. They are also used to produce negative pressures for industrial vacuum systems. Major types are: centrifugal blower and positive-displacement blower. Centrifugal Blowers Centrifugal blowers look more like centrifugal pumps than fans. The impeller is typically gear-driven and rotates as fast as 15,000 rpm. In multi-stage blowers, air is accelerated as it es through each impeller. In single-stage blower, air does not take many turns, and hence it is more efficient. Centrifugal blowers typically operate against pressures of 0.35 to 0.70 kg/cm2, but can achieve higher pressures. One characteristic is that airflow tends to drop drastically as system pressure increases, which can be a disadvantage in material conveying systems that depend on a steady air volume. Because of this, they are most often used in applications that are not prone to clogging.


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Working Principle Centrifugal blowers provide a steady volume of air to supply energy-efficient pressure or vacuum. Air enters at the center of a spinning impeller, and is divided between the impeller’s vanes. As the impeller turns, it accelerates the air outwards using centrifugal force. This high-velocity air is then diffused and slowed down in the surrounding blower housing to create pressure. The pressure or vacuum offers a wide range of volumetric flows possible due to the geometry of the open impeller. Advantages of Centrifugal Air Centrifugal air is energy-efficient and inexpensive, especially when compared to compressed air as an alternative. Centrifugal blowers use much less horsepower to create flow, thus using less energy than compressed air. When replacing compressed air, centrifugal blowers can offer a payback of months or even weeks.

Positive-Displacement Blowers Positive-displacement blowers have rotors, which "trap" air and push it through housing. Positive-displacement blowers provide a constant volume of air even if the system pressure varies. They are especially suitable for applications prone to clogging, since they can produce enough pressure typically up to 1.25 kg/cm2 - to blow clogged materials free. They turn much slower than centrifugal blowers (e.g. 3,600 rpm), and are often belt driven to facilitate speed changes. Working Principle If you were to dissect a PD blower you will notice that the main parts of the machine are two rotors that are ed together by gears surrounded by a blower casing. Many blowers also come with a sound absorber, air screen and other parts to improve efficiency, but when explaining how the apparatus functions we only need to focus on the rotors (often called the impeller), blower casing, inlet side and outlet side of the machine.


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Once a blower is in operation both rotors will rotate at the same speed but in opposite directions in order to draw air into the blower. One rotor is called the “driving rotor” because it is run by an external power supply, while the opposite rotor is called a “driven rotor” because it is driven by gears connected to the driving rotor. As the rotors revolve, air is pulled into the inlet side of the blower and is confined to tight areas between the rotors and the blower casing. This pocket of air is moved around the rotors and blower casing to the outlet side. Once the rotors open to the outlet side, the discharge line equalizes the pressure of the air and is forced out of the blower. The air is unable to come back due to the small amount of internal clearance between the internals of the machine. This process enables the blower to overcome line pressure hence the name positive displacement. Put differently, the volume of air does not change within the device, but is rather displaced from one end of the machine to the other. Below is an excellent illustration that explains the flow of air through the blower:

The load resistance of the material carried in the discharge line helps to create more pressure which in turn improves the functionality of the machine. In fact, many positive displacement blowers need some sort of back pressure to generate a substantial pressure reading to propel the materials or gas handled in the system.

Types of Positive Displacement Blowers Positive displacement blowers typically utilize a straight lobe rotor design with two or three lobes and are characterized as twin lobe rotary air blowers and tri-lobe rotary air blowers. A twin lobe blower contains two figure 8 shaped lobes while a tri-lobe blower consists of three lobes shaped like a boat propeller. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Twin Lobe vs. Tri-Lob

Tri-lobe blowers are considered much less noisy than twin lobe blowers because the three lobe blower design allow for lower pulsation levels and reduced noise. Common Applications of PD Blowers As stated, PD Blowers are used in a variety of applications and industries making them a desired investment to improve processes and cut lead times. Listed below are some common applications of PD blowers:              

Chemical - Vacuum Processing & Conveying Dairy - Automated Milking Environmental Services - Sewer Cleaning & Portable Cement & Lime - Fluidization & Conveying Resin & Plastic - Processing & Conveying Process Gas - Gas Boosting Soil Remediation - Vacuum Extraction & Sparging Industrial - Material Vacuuming Milling & Baking - Blending & Conveying Dry Bulk Hauling - Trailer Unloading & Aeration Power Generation - Fly Ash Conveying & Aeration Pulp & Paper - Chip Conveying & Process Vacuum Oil & Gas - Gas Collection & Sparging Aquaculture – Aeration

COMPRESSORS TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Compressors are used to increase the pressure of a fluid. The main type of compressor is the rotary compressor, meaning a rotary device is used to compress the fluid. Reciprocating and centrifugal compressors are the most common. A. Rotary 1. Sliding Vane Sliding vane compressors are widely used as vacuum pumps as well as compressors. General Information The sliding vane compressor is a rotary type compressor, meaning a rotating device is used to compress gas. Vanes on the rotor trap gas between the rotor and cylinder walls. This gas is compressed and released into the discharge line. Equipment Design The sliding vane compressor consists of a rotor mounted off-center in a cylinder slightly larger than the rotor. The rotor has a series of radial slots that hold vanes. These vanes are free to move in and out of the slots, but always maintain with the cylinder wall. The diagram shows a cutaway view of a sliding vane compressor. As the rotor turns and a pair of vanes approach the inlet, gas begins to fill the cell. As the rotation continues, the suction edge is ed by both of the vanes, sealing the cell of gas. The suction edge is the point where the vane first touches the cylinder wall. The vanes are pushed back into the rotor by the eccentricity of the cylinder wall. This decreases the volume of the gas cell, increasing the pressure of the contained gas. The compression continues throughout the rotation until the leading vane crosses the discharge port, releasing the compressed gas into the discharge line. Usage Examples Sliding vane compressors are versatile, finding applications in areas such as gas boosting, vapor recovery, and enhanced oil recovery. The gas compressor pictured below is used in biogas digester applications.


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 

Advantages Light weight machine Versatile



Disadvantages Low efficiency compared reciprocating compressors

to

2. Screw Screw compressors are also called helical-lobe compressors. General Information Screw compressors are positive displacement, intermittent, rotary compressors. This type uses two intermeshing lobes to compress gas. Oil-Injected Screw (OIS) compressors inject oil into several key areas of the compressor to provide lubrication, sealing, cooling, corrosion inhibiting, and noise dampening. The choice between OIS and Oil-Free Screw (OFS) compressors depends on the specific process requirements and tendencies. Equipment Design Screw compressors use the intermeshing of two rotors in the form of a helix. The male rotor has four convex lobes, the female rotor has six concave flutes like the ones shown above. Gas enters at the inlet port when the volume between the two is at its maximum. As the rotor turns, a lobe from the male rotor progressively enters the flute of the female rotor, decreasing the volume between the lobes and thus compressing the gas. The rotation of the rotor continues until the discharge port is reached, releasing the compressed gases. An oil-separation system and a lubrication system are used with oil-injected screw compressors. The oil-separator utilizes wire mesh demister devices for the separation of oil that gets into the gas and has a smaller storage tank to hold the separated oil. Usage Examples Screw compressors are used for applications requiring pressures between produced by reciprocating compressors and centrifugal compressors. Originally, compressors were primarily used in the petrochemical industries. Today, applications are in air and refrigeration services, and fuel gas markets. The rotary compressor pictured below is used to compress helium for industrial applications. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

those screw most screw

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

 

Advantages Ideal for applications with moderate flow rates and medium discharge pressures (pressures between those produced by reciprocating and centrifugal compressors) Liquid entrainment is easily flashed off Low maintenance required





Disadvantages Decreased efficiency if operated at a pressure ratio other than the designed pressure ratio Auxiliary components are expensive

3. Liquid Piston General Information/Equipment Design Liquid piston compressors perform compression with the use of a liquid ring acting as a piston. Like sliding vane compressors, this type has a rotor mounted off-center in a cylinder. Forward curved vanes are attached to the rotor. A liquid compressant partially fills the cylinder, forming a ring of liquid on the inside wall of the cylinder. Because the rotor is off-center, the volume between the ring and the rotor varies. This volume is maximum at the inlet port, where a pocket of gas enters. As the rotor turns, the gas is carried with it. As the volume between the liquid ring and the rotor decreases, the liquid acts as a piston, compressing the trapped gas. This gas is then released at the discharge port. 

Advantages Operation is not affected by the intake of liquid

Disadvantages 

Low efficiency


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4. Straight Lobe General Information/Equipment Design Straight lobe compressors have two rotors that intermesh as they rotate. These rotors usually have two lobes, although three lobe compressors are available, such as in the compressor pictured in the right. Gas is trapped and carried between the lobes as they the inlet port. The lobes push the gas toward the exit. Compression occurs due to the back pressure of the gas in the discharge line.



Advantages No internal gas compression



Disadvantages Limited pressure range

B. Other 1. Reciprocating Reciprocating compressors are the most widely used type of compressor. General Information Reciprocating compressors are positive displacement, intermittent compression devices analogous to a typical bicycle pump. Gas enters a chamber controlled by a piston. Pushing the piston down reduces the volume of the gas, causing an increase in pressure. This high pressure air is then pushed out of the chamber. Equipment Design The cylinder begins the cycle filled with gas at the intake pressure. The piston strokes inwards, decreasing the volume of the cylinder and therefore increasing the pressure. Once the desired pressure of the gas is reached, the discharge valve opens, and the piston pushes some of the high pressure gas out. At the end of the stroke, the piston reverses direction. Once the pressure of the remaining gas in the cylinder is the same as the intake pressure, the intake valve opens, refilling the cylinder. TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Reciprocating compressors consist of a single cylinder or multiple cylinders on a frame. Inside the cylinders, pistons reciprocate, compressing the gas. Single-stage compressor consists of a single cylinder or multiple cylinders in parallel. A multistage compressor consists of multiple cylinders in series. The reciprocating compressor is further categorized into two: single-acting; and double-acting cylinder. 1. Single-acting A single-acting cylinder in a reciprocating engine is a cylinder in which the working fluid acts on one side of the piston only. A single-acting cylinder relies on the load, springs, other cylinders, or the momentum of a flywheel, to push the piston back in the other direction. Singleacting cylinders are found in most kinds of reciprocating engine. They are almost universal in internal combustion engines (e.g. petrol and diesel engines) and are also used in many external combustion engines such as Stirling engines and some steam engines. They are also found in pumps and hydraulic rams. 2. Double-acting A double-acting cylinder is a cylinder in which the working fluid acts alternately on both sides of the piston. In order to connect the piston in a double-acting cylinder to an external mechanism, such as a crank shaft, a hole must be provided in one end of the cylinder for the piston rod and this is fitted with a gland or 'stuffing box' to prevent escape of the working fluid. Double-acting cylinders are common in steam engines but unusual in other engine types. Many hydraulic and pneumatic cylinders use them where it is needed to produce a force in both directions. A double-acting hydraulic cylinder has a port at each end, supplied with hydraulic fluid for both the retraction and extension of the piston. A double-


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acting cylinder is used where an external force is not available to retract the piston or where high force is required in both directions of travel. Usage Examples Most reciprocating compressors are used to generate pressurized air. The compressors shown below are used to pressurize air in healthcare facilities. The most common applications in refineries are hydrogen-rich streams, refinery fuel gas, and refrigeration systems.





Advantages Especially useful for low to moderate flow rates, low molecular weight gases, and high required discharge pressures Easily multi-staged

    

Disadvantages Low capacity Low reliability due to many wearing parts High maintenance required Little flexibility in material choices Pulsation and unbalanced forces created by reciprocating motion

DYNAMIC COMPRESSORS It is also called as Continuous-Flow Compressors and also classified as Turbomachines. These are machines where the flow of the gas is continuous. These types of machines are widely used in the chemical and petroleum industry for many services. They are also used extensively in many other industries such as the iron and steel industry, pipeline boosters, and on offshore platforms for reinjection compressors. Dynamic compressors are usually much smaller in size and produce much less vibration than the positive displacement compressors. 1. Centrifugal Centrifugal compressors are widely used, second only to reciprocating compressors in number of machines in the process industries because of their size and ease of use. Shown below is an integrally geared, multistage centrifugal compressor.


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General Information Centrifugal compressors are dynamic compressors, meaning energy is transferred from a moving set of blades to the gas. This energy takes the form of velocity and pressure. Equipment Design Centrifugal compressors use an impeller consisting of radial or backward bending blades. As the impeller rotates, gas between the rotating blades is moved from the area near the shaft radially outward into a diff. Energy is transferred to the gas while it is travelling through the impeller. Some of the energy results in an increase in pressure, some contributes to the velocity of the gas. This velocity decreases in the diff, resulting in a higher pressure and compression of the gas. Centrifugal compressors are often built in a multistage configuration, where several impellers are installed in one frame and operate in series as shown in the animation below. In a single-stage centrifugal compressor (shown upper to the right) one impeller is used and is often overhung. The air pressure increases after each impeller, allowing the multistage compressor to obtain higher pressures than a single stage compressor. Both types of centrifugal compressors can also be modified to it or extract vapor from or to side streams with the use of strategically placed nozzles. Centrifugal compressors are dynamic compressors, meaning energy is transferred from a moving set of blades to the gas. This energy takes the form of velocity and pressure. The compressor shafts are made from low-alloy steel or sometimes from corrosion-resistant materials. Most impellers are also made from low-alloy steel and come in two types: a closed impeller and a semi-open impeller. In closed impellers the blades and hubs are covered while in semi-open, often called open, impellers the impellers are not covered. Closed impellers can reach maximum allowed speeds of 310 m/s and semiopen impellers can reach 400 m/s. Usage Examples Originally, centrifugal compressors were used exclusively in steam turbines, but now they are also used in process plants as well as natural gas and petrochemical plants. The multistage compressor shown below is used to recycle hydrogen in an oil refining process.


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

 

Advantages Useful for large flows, high molecular weight gases, and high pressures Large flows can be compressed with high pressure capability High reliability

   

Disadvantages Limited choice of pressure ratio Large energy consumption High repair cost Low efficiency

2. Axial General Information/Equipment Design Axial compressors are high speed, large volume compressors in which gas flows axially through the machine. They are typically used for high flow and relatively low pressure applications. The energy from the rotor is transferred to the gas by rows of rotating blades. The rows of blades alternate with stationary sections called stators. The gas enters through the first stator, referred to as the guide vane row, and is acted upon by the rotor. The gas exits to the next stator row, and continues in the axial direction alternating rotor and stator rows. As the gas travels through the compressor, its pressure increases, resulting in compression. Working Principle In the axial compressor, the air flows parallel to the axis of rotation. The compressor is composed of several rows of airfoil cascades. Some of the rows, called rotors, are connected to the central shaft and rotate at high speed. Other rows, called stators, are fixed and do not rotate. The job of the stators is to increase pressure and keep the flow from spiraling around the axis by bringing the flow back parallel to the axis. The stators of a compressor are connected to the outer casing. The compressor is attached to a shaft which is connected to the power turbine on the right end of the blue shaft.  

Advantages Very high efficiency Highly sophisticated compressor



Disadvantages Very expensive


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REFERENCES: Blocker and Wallace Service LLC. (2017, September 3). Retrieved from http://www.blockerandwallace.com/what-is-a-positive-displacement-blowerBlog.html Bureau of Energy Efficiency. (2017, September 5). Retrieved from Fans and Blowers: https://www.saylor.org/site/wp-content/s/2011/09/Chapter-3.5-FansBlowers.pdf Campbell, D., Brown, N., & Cox, J. (2015). Centrifugal Pumps. Retrieved from Colorado State University: https://www.engr.colostate.edu Centrifugal Pump. (n.d.). Retrieved from Saylor Academy: https://www.saylor.org/ Centrifugal Pump. (n.d.). Retrieved from Grundfos: http://machining.grundfos.com Centrifugal Pump Types. (n.d.). Retrieved from Pump World: http://www.pumpworld.com Evans, J. (n.d.). A Brief Introduction to Centrifugal Pumps. Retrieved from Pacific Liquid: http://www.pacificliquid.com Henshaw, T. L., 1987, Reciprocating Pumps, New York, New York: Van Nostrand Reinhold Company. Holland F. A., F. S. Chapman. 1966. Pumping of Liquids. Reinhold Publishing Corporation, New York. Hydraulic Handbook. 1979. Colt Industries, Fairanks Morse Pump Division, Kansas City, Kansas Jorgensen, R. (n.d.). Fan Engineering. Buffalo Forge Company. Karassik, I., Messina, J., Cooper, P., and Heald, C., 2001, Pump Handbook, Third Edition, New York, New York: McGraw Hill. Mechanical Science Volume 1. (n.d.). Retrieved from Integrated Publishing: http://nuclearpowertraining.tpub.com Miller, J. E., 1987, The Reciprocating Pump—Theory, Design, and Use, New York, New York: John Wiley & Sons, Inc. Norrie. (2010, March 27). Centrifugal Pumps. Retrieved from Compression Jobs: compressionjobs.com Ordway, E. P., 1921, Union Engineering Handbook—Pumping Machinery, Air Compressors, and Condensers, First through Eleventh Editions, Battle Creek, Michigan: Union Steam Pump Company TRANSPORTATION OF FLUIDS: Pumps, Fans, Blowers, and Compressors – GARCIA, MALIWAT, SISON, YUMUL

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Republic Manufacturing. (2017, September 5). Retrieved from Website Pipeline: https://www.republic-mfg.com/blowers/republic-centrifugal-blower.asp Rusamsi, D. (2011, June 13). Scribd. Retrieved from How Centrifugal Fans Work: https://www.idoub.com/doc/57736970/How-Centrifugal-Fans-Work Sahdev, M. (n.d.). Centrifugal Pumps: Basics Concepts of Operation, Maintenance, and Troubleshooting, Part I. Retrieved from ChE Resources: cheresources.com Scramlin, J., Schneidkraut, M., Wozniak, A., Africa, M., Wesorick, S., Kaplan, K., & Plegue, T. (n.d.). Visual Encyclopedia of Chemical Engineering. Michigan: University of Michigan.


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