A simple, basic comparison of two of the most used pump types in the world!

The centrifugal pump is the most used pump type in the world. The principle is simple, well-described and thoroughly tested, and the pump is robust, effective and relatively inexpensive to produce.

Positive displacement pumps, on the other hand, operate by forcing a fixed volume of fluid from the inlet pressure section of the pump into the discharge zone of the pump. Positive-displacement pumps frequently are used in hydraulic systems at pressures ranging up to 5000 psi.

Lobe pump is a type of positive displacement pump that offers superb sanitary qualities, high efficiency, reliability, corrosion resistance, and good clean-in-place and sterilise-in-place (CIP/SIP) characteristics.

Before selecting the right pump for the job, we need to understand:

  1. Total head or pressure against which it must operate
  2. Desired flow rate
  3. Suction lift
  4. Fluid characteristics (temperature, corrosiveness, etc.)

The piping system and pump interact to determine the operating point of pumps: flow rate and pressure.

Basic Comparison

Centrifugal Positive Displacement
Mechanics 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).
Performance Flow varies with changing pressure. Flow is constant with changing pressure.
Viscosity Efficiency decreases with increasing viscosity due to frictional losses inside the pump (typically not used on viscosities above 850 cSt). Efficiency increases with increasing viscosity.
Efficiency Efficiency peaks at best-efficiency-point. At higher or lower pressures, efficiency decreases. Efficiency increases with increasing pressure.
Inlet Conditions 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.

If you need assistance with your pump selection, please contact All Pumps today.