Positive displacement pumps displace a fixed volume of fluid with each cycle or rotation. They are capable of developing high pressures at low suction pressures, unlike centrifugal pumps whose capacity is affected by outlet pressure. There are two main types of positive displacement pumps: rotary pumps which displace a fixed volume per revolution using components like gears or screws; and reciprocating pumps which use pistons or diaphragms moving back and forth in a cylinder. Reciprocating pumps are generally more efficient and suitable for high-pressure, low-volume applications while rotary pumps have lower fuel consumption and noise. Both have advantages for different industrial uses.

1. POSITIVE DISPLACEMENT MACHINES used
for industries

3. Positive displacement pumps were developed long
before centrifugal pumps. Liquid is positively
Displaced from a fixed-volume container. Positive
-displacement pumps are capable of developing
high pressures while operating at low suction
pressures.

4. They are commonly referred to as
constant-volume pumps. Unlike
centrifugal pumps.
Their capacity is not affected by the
pressure against which they operate. Flow
is usually regulated by varying the speed
of the pump or by recycle.

6. A pump can be classified in to three types
according to the method they use to move
the fluid
1.Direct lift pumps
2.Displacement pumps
3.Gravity pumps
Here we discuss about displacement pumps

7. positive displacement pumps are divided in to
Two types
1.Rotary water pumps
2.Reciprocating water pumps
Rotary water pump: it is usually used to displace
Lubrication oils for Engines, Turbines, Machines,
Gears etc...
It displaces fixed volume of fluid for every
revolution

8. Main components of rotary pump
1.Slidingvalve
2.External gear
3.Internal gear
4.Lobe
5.Singlescrew
6.Multiple screw

10. Advantages of Rotary pump
1.Low fuel consumption
2.Low toxic emission
3.Easy and adaptable to a variety
of engine
4.High injection pressure
5.Less noise level

11. Disadvantages of Rotary pump
1.High initial cost
2.Skill required for overhaul

12. 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. They can handle viscous and abrasive
fluids.

13. 1.Plunger or piston pumps:
Here piston or
Plungers are used to push or pull the liquid
2.Diaphragm pump:
Here a flexible pulsating diaphragm is
used

15. Advantages of reciprocating pump:
1.High efficiency of 85-94%
2.Require less horse power
3.Best suited for high-pressure and
Low-volume applications

16. Disadvantages of reciprocating pump:
1.They require pulsation dampers
Because of pulsating nature of flow
2.Higher installation costs
3. Higher maintanence than CFP’s

17. Comparison with centrifugal pump
Centrifugal pump Positive displacement
pump
Imparts velocity to the
liquid resulting in a
pressure at the outlet
(pressure is created and
flow results).
Captures confined
amounts of liquid and
transfers it from the
suction to the discharge
port (flow is created and
pressure results).

18. Flow varies with changing
pressure
Flow is constant with
changing pressure.
Efficiency decreases with
increasing viscosity due to
frictional losses inside the pump
(typically not used on viscosities
Efficiency increases with
increasing viscosity.
Efficiency peaks at best-
efficiency-point. At higher or
lower pressures, efficiency
decreases
Efficiency increases with
increasing pressure.
Liquid must be in the pump to
create a pressure differential. A
dry pump will not prime on its
own.
Negative pressure is
created at the inlet port. A
dry pump will prime on its
own.

19. Centrifugal pumps are replaced by
Displacement pumps. Displacement
Pumps are suitable for small and large
operations at any pressure and volume

20. Scope of future works:
1.All high speed and diesel Engines
require positive displacement pump
2.Achieving high pressure flow
3.Required for future hybrid cars