Centrifugal Pumps vs. Positive Displacement Pumps

Centrifugal and positive displacement pumps share many similar characteristics, however they do have some crucial differences that make them suitable for certain applications. Here are the features that distinguish centrifugal from positive displacement pumps, and when you might choose to use each type.

Centrifugal Pumps

In a centrifugal pump, an impeller rotates and creates a vacuum in order to move fluid to the impeller, the impeller in turn creates fluid velocity as the fluid passes through. This velocity is converted into pressure by the pump casing as the fluid moves through to the discharge port. Centrifugal pumps are a popular choice within the mining, manufacturing and agricultural industries due to their relatively small size and easy maintenance.

Centrifugal pump characteristics

  • Flow of fluid varies according to changing pressure.
  • Best used with lower viscosity fluids, as higher viscosity can cause friction.
  • Efficiency peaks at a specific pressure, and any pressure variations tend to decrease efficiency.
  • Most centrifugal pumps cannot be run dry.

What are centrifugal pumps used for? 

This type of pump has many different applications and is suitable for low viscosity fluid and high flow rates.  As such, a centrifugal end suction pump (or ISO pump) can offer superior transfer of fluids.  This type of pump can transfer thin fluids like water, thin chemicals and thin petroleum products. Centrifugal pump design options include Radial flow impeller design, Axial flow impeller design and Mixed flow impeller design. They can also have Volute type casings and Diffuser type casings.  MTP supplies ISO pumps with a choice of casing and impeller materials to suit a variety of needs.

Positive Displacement Pumps

In a positive displacement pump, fluid is drawn into a fixed-volume compartment at the inlet and moved to the outlet by means of either a reciprocating or rotary motion to cause pressure. One major advantage with this type of pump is that the pressure at the inlet has little effect on the consistent flow of fluid, which is why they are commonly referred to as constant-volume pumps.

Positive displacement pump characteristics

  • Flow of fluid remains relatively consistent, regardless of pressure up to the pump design limits.
  • Often works more effectively with higher viscosity fluid.
  • Efficiency tends to increase as pressure increases.

What are positive displacement pumps used for?

As positive displacement pumps operate at a constant flow and work well with high viscosity fluids, they’re suitable for use with thicker liquids such as oils, greases, pastes, slurries and creams. Pump types include peristaltic, gear, lobe, twin screw, diaphragm, and progressive cavity pumps amongst many others. MTP supplies air diaphragm pumps, chemical dosing pumpsmembrane pumps and progressive cavity pumps to suit a wide range of applications across mining, construction,agriculture and more.

The type of pump you require will depend on the total pressure against which the pump must operate, the required flow rate, suction lift, and the characteristics of the liquid being displaced. For assistance in identifying the right pump system for your needs, call MTP now on 1800 439 607 or contact us. We’ll be happy to provide expert advice and tailor a pump package to suit your needs.

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