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Positive displacement machines

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Positive displacement machines

  1. 1. POSITIVE DISPLACEMENT MACHINES used for industries
  2. 2. 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.
  3. 3. 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.
  4. 4. 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
  5. 5. 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
  6. 6. Main components of rotary pump 1.Slidingvalve 2.External gear 3.Internal gear 4.Lobe 5.Singlescrew 6.Multiple screw
  7. 7. 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
  8. 8. Disadvantages of Rotary pump 1.High initial cost 2.Skill required for overhaul
  9. 9. 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.
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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).
  14. 14. 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.
  15. 15. Centrifugal pumps are replaced by Displacement pumps. Displacement Pumps are suitable for small and large operations at any pressure and volume
  16. 16. 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
  • SwaroopKashetty

    Nov. 3, 2020
  • AjayPatidar21

    Sep. 23, 2018
  • neorit1000

    Apr. 17, 2016

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