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 = Pf/PB
Where, Pf is the fluid power
in the pump
PB 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.
