A Presentation On Pumps 2m5751

A Presentation on Pumps by Awais Abdullah BC-M6-308

Institute of Chemical Engineering and Technology. University of the Pujnab. Lahore

Table of Contents • • • •

Introduction to pumps Types of pumps Introduction to Pd pumps Fundamental calculations of Pd pumps – Pump displacement – Capacity of pd pumps – Volumetric efficiency – Mechanical efficiency – NPSH – Vapor locking / Cavitation

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Types of Pd pumps – Reciprocating • Piston pumps ( simplex/ duplex/ triplex) • Plunger pumps • Diaphragm pumps • Power pumps and direct acting pumps –

Rotary pumps • Single rotor (lobe pump, vane pump) • Multiple rotor (Gear pump, Screw pump)

Introduction to Pumps. • A pump is a physical contrivance that is used to deliver fluids from one location to another through conduits. • Pump is a machine that applies or adds energy to the fluid to move it from one position to another.

Types of Pumps • There are four major types of pumps – Positive displacement – Dynamic (kinetic) or centrifugal pumps – Lift pumps – Electromagnetic pumps

Introduction to PD pumps: • A pump that displaces a constant volume of the liquid is called a positive displacement pump. • Pd pumps are pressure pumps. • They are rated by the maximum pressure they can apply to the luiquid. • Pressure applied depends on –Area of piston –Force applied to the piston

Fundamental calculations of PD Pumps 1. 2. 3. 4. 5. 6.

Pump Displacement Capacity of Pd pumps Volumetric Efficiency Mechanical Efficiency NPSH Vapor locking / Cavitation

1. Pump displacement • The volume of the liquid that a pump can move in one revolution if there were no leakage of loss is the pumps displacement • Pump displacement = (area of the piston) * (length of the stroke) – ( A double acting pump has two displacements per revolution. )

Diameter of piston

Length of the stroke

2. Capacity of PD pumps • The capacity of the pump is the volume of the liquid it moves in a given period of time. • ( Capacity may be in Gallons/min GPM or lb/min or ft3/min ) • Capacity of the PD pumps is of two types – Actual capacity – Theoretical capacity

Types of Capacity of the PD pumps • Theoretical capacity = volume of the liquid displaced (Pumps displacement) * RPM.

• Actual capacity = From flow measuring device. • Actual capacity < Theoretical capacity – ( Due to slippage )

• Capacity can also be calculated in lb/min as follows – Capacity = Capacity in ft3/min * 62.4 * SP. GR.

3. Pumps Volumetric Efficiency • The ratio of the pumps actual capacity to the theoretical capacity is called pumps volumetric efficiency. • Volumetric efficiency = ( Actual capacity / Theoretical capacity ) * 100 • Well operated and properly maintained PD pumps usually have volumetric efficiencies between 70 to 85%.

4. Mechanical efficiency • MA is the percentage of the HP ( horse power ) received that is actually applied to the pumping liquid. – MA α ( 1 / HP )

• Overall efficiency is the fluid HP divided by the mechanical HP. – Overall efficiency = ( Fluid HP/Mechanical HP ) * 100

• Mechanical HP is the HP received form the prime mover. • Fluid HP is the HP transmitted to the fluid.

5. NPSH • Pressure is required at the suction of the pump and a pump cannot fill without adequate suction pressure. • The vertical distance from the liquid level to the pump intake is called net positive suction head. • NPSH is the net positive pressure at the pump suction, calculated as head in feet. • Condition of pump operation: – NPSH available > NPSH required • ( This is to avoid cavitation or vapor locking )

Suction pressure is provided by suction systems that are: • Suction head system • Suction lift system

Suction Head System • In suction head system the pump is below the level of the liquid in the suction tank. • Here the static pressure of the liquid is available to move the liquid in the pump.

Suction lift System • In suction lift system the pump is above the level of the liquid in the suction tank. • In suction lift system the static pressure of the liquid must be overcome to lift the liquid to the pump. ( Suction lift for PD pumps is 22 ft )

– The energy added to the pump is called total head

6. Vapor locking / Cavitation • Sometimes as the liquid at the suction of the pump vaporizes due to low pressure and high temperature. • A pump can be damaged in the presence of the vapor leads to vapor locking or Cavitation. • Pressure can be calculated as the head of the liquid – Head = [ Pressure / ( 0.433 * SP. GR.) ]

• Prevention of Cavitation: – To prevent vaporization of the liquid at the pumps suction absolute suction pressure may be higher than the vapor pressure at a pumping temperature. – The PD pumps create a positive suction hence they are called SELF PRIMING

1. Reciprocating The flow of liquid from a reciprocating pump is pulsating

• Piston pumps – On the basis of no of pistons • Simplex • Duplex • Triples

– On the basis of displacement of liquid • Single acting • Double acting

• Plunger pumps • Diaphragm pumps • Power pumps and direct acting pumps

Piston pumps (On the basis of no of pistons)

Simplex • The Simplex, or Single-Cylinder Double Acting, Pump was invented in 1840 by Henry R. Worthington. • A Simplex pump, sometimes referred to as a single pump, is a pump having a single liquid (pump) cylinder. • A Simplex Pump is a reciprocating pump. This pump has a single liquid cylinder which forces liquid out through the top outlet on both the in and the out stroke • This basic type of pump might be used for Air Pumps, Feed Pumps for the furnace, Fire, Bilge, and Fuel Oil Service. All might rely on this fundamental pump.

Piston pumps (On the basis of no of pistons)

Duplex

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A duplex pump is the equivalent of two simplex pumps placed side by side on the same foundation. The driving of the pistons of a duplex pump is arranged in such a manner that when one piston is on its upstroke the the piston is on its down stroke, and vice versa. This arrangement doubles the capacity of the duplex pump compared to a simplex pump of comparable design. The Duplex pumps is similar to the Simplex pump, having two pistons instead of one, providing smoother operation.

Piston pumps (On the basis of no of pistons)

Triplex • The triplex pump is similar to the Simplex pump, having three pistons instead of one, providing smoother operation. • Discharge is smoother if the pump is multiplex.

Piston pumps On the basis of displacement of liquid

Single Acting

• If the liquid is displaced on the forward stroke only the pump is single acting. • At the beginning of the forward stroke both cylinder valves are closed. • As the piston moves forward, cylinder pressure forces the discharge valve to open. • Then a volume of the liquid is displaced at the forward stroke.

Piston pumps On the basis of displacement of liquid

Double acting

• If the liquid is displaced on forward as well as backward stroke then the pump is called double acting pump. • On the forward stroke liquid enters the crank end of the cylinder and is displaced from the head end of the cylinder. • In double acting pump the rod reverses direction at the end of each stroke. • Discharge is very much smoother if the pump is double acting.

Plunger Pumps

• It uses plunger instead of piston. • It is used for high pressure services and for the liquids that are sticky in nature. • The plunger does not fits close to the wall of the cylinder.

Plunger Pumps • Plunger displaces a volume of the liquid equal to its volume during operation. • Plunger is made of cast iron or cast steel or may be made of stoneware.

Diaphragm pumps • For slurry and corrosive liquids diaphragm pumps may be used. • Used for pumping corrosive liquids with a high percentage of solids. • The plunger is protected by a flexible rubber.

Diaphragm pumps • The plunger is protected by a flexible rubber. • The liquid is least likely to flash into vapor at the suction of diaphragm pump because the diapharm maintains some pressure on the suction liquid. • Where NPSH is low diaphragm pump is used

Power pumps and direct acting pumps:

• A pump that is powered by a separate prime mover or driver is a power pump. • A motor engine or a turbine may supply power to drive the pump. The rotary motion of the driver shaft is converted to the reciprocating motion of the prime mover. • Speed and RPM can be adjusted • Direct acting pumps – Reciprocating pumps powered by steam or some compressed air are direct acting.

2. Rotary pumps – Single rotor • Vane pump

– Multiple rotor • Lobe pump • Screw pump • Gear pump

Single rotor

Vane pump • In a sliding vane pump a set of vanes is mounted in a rotor. • These vanes slide in and out of the rotor. The sliding vane pump has two suction ports. • The vanes make a close seal against the casing wall. • The vanes are in slots in the rotor. When the rotor spins, centrifugal force pushes the vanes out to touch the casing, where they trap and propel fluid. • When the vanes reach the return side they are pushed back into the rotor by the casing. Fluid escapes through a channel or groove cut into the casing

Multiple rotor

Lobe pump • The drawing shows the lobe pump. • Each pump has two rotors. • Each rotors has two lobes. • The rotors are mounted on the separate shafts.

Multiple rotor

Gear pump • This is a type of Rotary Force Pump. Gear pumps are extremely simple and reliable. • Depending on the number of teeth, the "idler" gear might be driven directly by the "drive" gear. Generally with six or more teeth this is possible. • This pump will pump in the reverse direction if you reverse the direction of rotation of the gears.

Multiple rotor

Gear pump • The teeth on Gear Pumps can be spur (straight), helical (slanted), etc. • There can be two, or more teeth on each gear. • The diameter of the gears and their thickness varies widely

Multiple rotor

Screw pump