Comparison Between Centrifugal Pump And Positive Displacement Pump | Mecholic -->

Comparison Between Centrifugal Pump And Positive Displacement Pump


🔗Classification of pumps - Rotodynamic pump and Positive displacement pump

Working mechanism

The centrifugal pump has a spinning impeller that draws the fluid from the inlet area and forces it out at the outlet area of the pump. They are used to pump low viscous fluid where a high flow rate is required. Examples: Municipal water supply system, irrigation, cooling tower, boiler feed, and firefighting.

In the displacement pump, the fluid is first drawn to a confined cavity, displacing it by reducing cavity volume and forcing it out through the discharge nozzle. They are used for high-pressure and low-flow rate applications with viscous fluids. Examples: Municipal sewage systems, oil processing centers, paper pulp.


 🔗Main components and working principle of a centrifugal pump

What are the advantages of a centrifugal pump over a positive displacement pump?

Centrifugal pump has the following advantages over positive displacement pump

  • The centrifugal pump has a simplistic design and fewer components than the positive displacement pump, so it is less expensive.
  • The installation and maintenance are very easy, and it is also cheaper.
  • They are smaller, lighter, and require less space than reciprocating pumps for the same capacity and energy transfer. Its compact design enables it to be used in confined spaces.
  • They are more efficient than reciprocating pumps.
  • Produce a smooth and non-pulsating discharge.
  • It has a substantially larger discharging capacity than a reciprocating pump.
  • It the suction head is low, they can operate at higher speeds without the risk of separation and cavitation.
  • They can be directly coupled to electric motors or oil engines. 
  • They are commonly used in high-volume applications that demand high flow rates at low pressures.
  • Over-pressure protection is not necessary for a centrifugal pump. For PD pump, over-pressure protection is necessary.

What are the advantages of a positive displacement pump over a centrifugal pump?

  • The positive displacement pump can pump highly viscous liquids like sugar molasses, oil, and paper pulp. It has ability to handle solid particles varies tremendously, like pumping sewage water, etc., while a centrifugal pump can't handle even moderate viscous fluids well because of frictional loss. The efficiency of centrifugal pumps decreases as viscosity increases.
  • Positive displacement pumps are suitable for pumping shear-sensitive fluids. The impellers in centrifugal pumps pose a risk to the fluid.
  • Positive displacement pumps have the self-priming ability. It can operate in intermittently dry conditions and start without being primed by the liquid in the system. Centrifugal pumps must be primed to start the pressurized control. Standard models of centrifugal pumps cannot create a suction lift.
  • Positive displacement pumps maintain a constant flow rate even when the pressure changes. The flow rate is unaffected by flow restriction or fluid viscosity. However, the fluid exiting centrifugal pumps have a variable flow rate based on pressure.
  • The efficiency of a positive displacement pump is greater than that of a centrifugal pump. This is because positive displacement pumps can be run at any point on their curve without damage or efficiency loss. In contrast, in centrifugal pumps, efficiency peaks at a specific pressure, and any variations significantly reduce efficiency.
  • Positive displacement pumps are ideal for high-pressure and low-flow rate viscous fluid applications.

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