positive displacement machines

POSITIVE DISPLACEMENT MACHINES usedfor industries

SWAGATHA PANIGRAHISWAROOP.K.SSWAROOP.U.H

SYED ABDUL MUSAVIRSYED FAISAL RAZA

SYED AMEEN

UNDER THE GUIDENCE OF:PROF.ROBINSONBatch members:

INTRODUCTION:Machine in which fluid is forced in or out of chamber by changing volume of chamber

Is called as a positive displacement machine

EX: Compressor, water pump, Air pump. Etc

Industrial use: positive displacement pumps

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.

Literature survey:

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.

WHAT IS A POSITIVE DISPLACEMENT PUMP ?

It is a device that movesFluids by mechanical action.

A pump can be classified in to three types according to the method they use to movethe fluid1.Direct lift pumps2.Displacement pumps3.Gravity pumps

Here we discuss about displacement pumps

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 everyrevolution

Main components of rotary pump1.Slidingvalve2.External gear3.Internal gear4.Lobe5.Singlescrew6.Multiple screw

Rotary Vane Pump Animation.mp4

Advantages of Rotary pump1.Low fuel consumption2.Low toxic emission3.Easy and adaptable to a variety of engine4.High injection pressure5.Less noise level

Disadvantages of Rotary pump1.High initial cost2.Skill required for overhaul

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.

1.Plunger or piston pumps: Here piston or Plungers are used to push or pull the liquid2.Diaphragm pump: Here a flexible pulsating diaphragm is used

Types of reciprocating pump

reciprocating pump.mp4

Advantages of reciprocating pump:1.High efficiency of 85-94%2.Require less horse power3.Best suited for high-pressure andLow-volume applications

Disadvantages of reciprocating pump:1.They require pulsation dampers Because of pulsating nature of flow2.Higher installation costs3. Higher maintanence than CFP’s

Comparison with centrifugal pumpCentrifugal 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).

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.

Conclusion:

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

Scope of future works:1.All high speed and diesel Engines require positive displacement pump2.Achieving high pressure flow3.Required for future hybrid cars

Any?Thank you