Pumps - Types, Working Principle and Applications

 Different Types of Pumps with Working Principle and Applications

Pump

Pumps are the devices that impart pressure increase to a fluid and subsequently help to move the fluids by the mechanical action.

Uses of pumps

o   Irrigation

o   Water supply

o   Movement of sewage

o   Marine services

o   Waste water recycling

o   Control of flood

o   Refrigeration

o   Cooling system

Types of Pumps

Positive Displacement Pumps

• These types of pump displace a more or less fixed volume of fluid during each cycle of operation
• The volumetric flow rate is determined by the displacement per cycle of the moving member (either rotating or reciprocating) times the cycle rate
• The flow capacity is fixed by the design, size, and operating speed of the pump
• Positive displacement pumps have limited flow capacity but are capable of relatively high pressures
• These pumps operate at essentially constant flow rate with variable head
• These types of pumps are appropriate for high pressure requirements, high viscous fluids, and applications that require a precisely controlled or metered flow rate 

Piston Pump

It is a type of reciprocating pump

• Liquid is drawn through an inlet check valve  into the cylinder by the with drawl of a piston and then is forced out through a discharge check valve on the return stroke

o   It is double acting with liquid admitted alternately on each side of the piston so that one part of the cylinder is being filled while the other is being emptied

o   The maximum discharge pressure for commercial piston pumps is about 50 atm 

Plunger Pump

• It is a type of reciprocating positive displacement pump
• For higher pressures plunger pumps are used
• It can discharge against a pressure of 1500 atm or more
• The volume of the fluid discharged is equal to the area of the plunger multiplied by its stroke length
• Plunger pumps are single acting and usually are motor-driven
• Used for transferring municipal and industrial sewage 

Diaphragm Pumps

• It is a type of reciprocating positive displacement pump
• It operates by the combination of reciprocating action of a flexible diaphragm and valves on either side of the diaphragm
• It can handled small to moderate amounts of liquid up to about 100 gal/min
• It can develop pressures in excess of 100 atm
• It is used for handling toxic or corrosive liquids 

Rotary Pumps

• Unlike reciprocating pumps, rotary pumps contain no check valves
• Discharge pressures up to 200 atm or more can be attained

• It is a self-priming pump
• It can give constant delivered capacity regardless of the pressure

• Broad way rotary pump can be classified as single rotor and multiple rotor pump

• It operates best on clean and moderately viscous fluids; e.g. light lubricating oil 

Peristaltic pumps

o   It is a type of positive displacement pump

o   Commonly known as roller pumps

o   Peristaltic pumps may run continuously

• This type of pumps are used for variety of industrial applications and agricultural applications
• It is also used in heart-lung machines to circulate blood during bypass surgery and in hemodialysis systems 

Vane pumps

• It is a positive displacement pump
• Vanes are mounted to a rotor that rotates inside a cavity
• These pumps are suitable for low viscosity fluids
• Commonly used in high-pressure hydraulic pumps and in automobiles
• For mid-range pressures it is used as carbonators for fountain soft-drink dispensers and  espresso coffee machines

• For low-pressure gas applications it is used in secondary air injection for auto exhaust emission control 

Gear pumps

• It is a type of positive displacement pump
• The steps involved during pumping:

                        1. Gears separate on the intake side of the pump

                        2. Creating a void and suction which is filled by fluid

                        3. Fluid is carried by the gears to the discharge side of the pump

                        4. The meshing of the gears displaces the fluid

• They are mostly used for hydraulic fluid power applications

• These pumps are also widely used in chemical installations to pump high viscosity fluids 

Lobe pumps

• It is a type of positive displacement pump
• This pump can handle solids, slurries, pastes, and a variety of liquids
• It can pump larger size particles compared to the other positive displacement types pumps
• These types of pumps are used in different industries such as pharmaceutical industry, food industry, chemical industries, pulp and paper industries, etc. 

Screw pumps

• It is a positive displacement pump
• One or more than one screws are there to move fluids or solids along the screw (s) axis
• Fluid is moving axially without turbulence which eliminates foaming in viscous fluids
• It can pump fluids of higher viscosity without losing flow rate

• Generally used for transporting viscous fluids with lubricating properties

• Specific use includes oil burners, hydraulics, lubrication, etc. 

Centrifugal Pumps

• These pumps operate by the transfer of energy (angular momentum) from a rotating impeller to the fluid
• The fluid enters at the axis or ‘‘eye’’ of the impeller and is discharged from the impeller periphery
• Kinetic energy and momentum of the fluid are increased by angular momentum imparted by the high-speed impeller
• Kinetic energy is converted to pressure energy (head) in a diverging area (volute) between impeller discharge and casing before the fluid exits the pump
• Centrifugal pumps are most appropriate for ordinary (i.e. low to moderate viscosity) liquids 

Axial Flow Pumps

• It consists of a propeller in a pipe
• The propeller of the axial flow pump can be driven by a motor
• The pressure in an axial flow pump is developed by the flow of liquid over the blades of impeller
• These types of pumps are mainly used for handling sewage from commercial, municipal and industrial sources
• Axial flow pumps are also used in agriculture and fisheries to lift water for irrigation and drainage 

Radial Flow Pumps

• It is a type of centrifugal pumps where the fluid leaves the impeller in radial direction
• This type of pumps have higher discharge pressure because of higher centrifugal force
• The delivery head for this type of pumps is proportional to the impeller diameter.
• Applications of radial flow pumps include cooling systems, irrigation systems, filtration, water treatment, transporting chemicals, etc. 

Mixed Flow Pumps

• It is type of centrifugal pump with mixed flow impeller
• It has mixed features of radial flow pump and axial flow pumps
• Mixed-flow pumps operate at higher pressures than axial-flow pumps
• It can deliver higher discharges than radial-flow pumps
• This types of pump are used in different industrial applications, especially in propel water crafts such as jet skis 

Peripheral Flow Pumps

• This is centrifugal pump, also called regenerative pumps
•  Here the fluid moves along the circumference from the inlet to the outlet of the casing
•  In general this types of pump are small in size
•  Efficiencies of a peripheral pump is lower than the radial flow pumps
• These types of pumps are mainly used for fire pumps, aircraft refueling, and in a small boiler feeding operations 

Gas Lift Pumps

• This type of pumps are used to lift fluids from wells
• High pressure gas is used to pump the fluid from the wells
• The high pressure  of the gas make the    fluid weight less
•  Gas lift pumps are used widely in pumping water, brine, and oil
• This types of pump can also be used in aquariums to keep water circulating 

Jet Pumps

• It is a type of velocity head pump
• Venturi nozzles is attached at the discharge outlet
• In general multiple inlets are used to draw a constant stream of fluids

o                   This types of pumps are used in vessels, ferries and in other types of marine applications 

Hydraulic Ram Pumps

o                   This type of pumps are cheap, easy to maintain and very reliable

o                   No external source of power is required in the operation of the pump

o                   It uses the water hammer effect to develop the pressure in the fluid

o                   It has two moving parts: a sprig and a delivery check valve

o                   Mainly used for rural community water supply and irrigation 

Electromagnetic Pumps

• This type of pumps can move fluids which are good electrical conductors
• A magnetic field is set at right angles to the direction the fluid moves in
• A current is passed through it to create electromagnetism

• The electromagnetic force helps to move the fluid
• These pumps are used for Pumping liquid metals Cooling nuclear reactors 

Submersible Pumps

• Whole body of the pumps is submerged in the fluid to be pumped
•  There is no problem in pump cavitation
• In general this types of pumps are more efficient than jet pumps
•  Applications of single stage submersible pumps are in drainage system, sewage pumping and slurry pumping
• Multistage submersible pumps are mostly used in residential, commercial, and industrial operations 

NPSH

o               Net positive suction head (NPSH) available is of extreme importance for reliable pump operation

o               To avoid cavitation in pump, the pressure in the pump inlet must exceed the vapour pressure by     a certain value, called the net positive suction head (NPSH). The equation of NPSH can be                written as:

                   The required value of NPSH is about 2 to 3 m for small centrifugal pump; but it increases                  with pump capacity, impeller speed, and discharge pressure, and values up to 15 m are                  recommended for very large pumps.

 

Affinity laws

• When a complete set of performance curves is not available, the characteristics of a particular pump can be predicted from a similar pump and the theoretical equations for an ideal pump
• The relationships between impeller size and speed with capacity, head, and power are called the affinity laws 

Capacity:       q α n   (constant D)                          q α D (constant n)

Head  :          ΔH α n² (constant D)                        ΔH α D² (constant n)

Power :          P α n³  (constant D)                          P α D³ (constant n) 

Efficiency of a Pump

• In general the pump efficiency can be defined as the ratio of water horsepower output from the pump to the shaft horsepower input for the pump.
• In another form the efficiency of a pump can be calculated as the ratio of fluid power to the total power consumed

                                                            η = P_f/P_B

Where, P_f is the fluid power in the pump

P_B is the power supplied to the pump

• Lower efficiencies of any pump are mainly because of the friction, leakages, etc. 

Pump priming

• If a centrifugal pump is filled with air when it is turned on, the initiation of pumping action may not be sufficient to bring the fluid into the pump. Pumps can be specified with features that can minimize priming problems
• A pump with air in its casing is air bound and can accomplish nothing until the air has been replaces by a liquid. Air can be replaced by priming the pump from an auxiliary  priming tank connected to the suction line or by drawing liquid into the suction line by a independent source of vacuum
• Positive-displacement pumps can compress a gas to a required discharge pressure and are not usually subject to air binding

References

1. Kreith, F .;  Berger, S.A.; et. al. “ Fluid Mechanics ” 1999.

2. Ron Darby, Chemical Engineering Fluid Mechanics, Second Edition, 2001.

3. McCabe W. L.; Smith, J. C.; Harriott, P. Unit Operations of Chemical Engineering. Fifth Edition, McGraw-Hill International Editions.

 

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