Types of Positive Displacement Pumps

Introduction

Positive displacement (PD) pumps are one of the two main kinds of pumps used for a variety of purposes in the food, fuel, oil production and pharmaceutical industries, plus many more.

Compared to their centrifugal pump counterparts, PD pumps vary significantly in their design and function. Learning the difference between each different kind of PD pump can be overwhelming.

In this blog, we’ll be going over the different kinds of positive displacement pumps to help you better understand what each type of PD pump does.

Purpose of Positive Displacement Pumps

Whereas a centrifugal pump moves by using the energy of motorised impeller to push fluids along, positive displacement pumps channel a fixed amount of fluid into their chambers and push them out of the discharge valve with a mechanism.

PD pumps are generally used to transfer high viscosity liquids like oils and sewage, whereas centrifugal pumps are better suited for low viscosity fluids such as water and light fuels.

The mechanism a PD pump uses ensures it will fall into one of two categories: reciprocating pumps that use mechanisms that pull and push fluid through the chamber, or rotary pumps which use rotating components to transport a fluid across the chamber.

Reciprocating pumps

First, let’s look at three different kinds of reciprocating positive displacement pumps:

• Piston type pumps draw in fluids through a check valve with vacuum that’s created by retracting a piston tightly hugging the walls of the chamber, which then pushes the fluid out when it extends.

• Plunger pumps operate in a similar manner to pistons but fits more loosely into its cylinder. By pushing in and out, the plunger’s mass constantly alters the size of the chamber and displaces the fluid.

• Rather different in design is the diaphragm pump, which uses a flexible component to change the volume of the chamber that means fluid is both drawn in and pushed out through its mechanism.
  

Rotary pumps

Coming in several different configurations, rotary pumps use components that rotate to process their fluids from one valve to another.

• Gear type pumps use the teeth of two spinning gears to move fluid through the chamber and push it out as the gears mesh together. These are available in both internal and external gear setups.

• Lobe pumps are very similar to gear pumps but instead use lobes to pick up the fluid entering the chamber and push it out as the lobes mesh closely together.

• Vane pumps use sliding vanes on a rotor to continuously change the volume of the pump’s chamber, pushing along all fluids to the exit valve with centrifugal force.

• A peristaltic pump channels liquid through a tube with a central component that rotates inside the casing, continuously pushing the fluid towards the outlet in a similar manner to a tube of toothpaste.

• Screw pumps generally use two or three screw shafts in close alignment to one another, using the motion of one shaft to capture fluid in the other screws’ threads and push it towards the casing outlet.

• A progressive cavity screw holds a helical rotor with a casing shaped like a double helix to fit its rotation. With its unique design, it pushes tough-to-handle fluids in a circular motion towards the exit outlet.
  

Conclusion

With so many kinds of positive displacement pumps available, it can be difficult to know where to start or what kind of pump is right for you.

At Kelair Pumps, we can use our 50 years of supplying pumps to Australian industries to help you find exactly what kind of PD pump your workplace needs.

Reach out today to discuss what you need and get a quote from the Australian pumping experts!