Positive displacement pumps play a critical role in fluid handling and processing applications across a wide range of industries. While centrifugal pumps have replaced them as the standard for low-pressure, high-volume pumping operations, they remain necessary for highly specialized pumping applications. The following article provides an overview of positive displacement pumps, outlining what they are, how they work, and the types available in the market.
What Is a Positive Displacement Pump?
Positive displacement pumps rely on a variety of rotating or reciprocating components—e.g., diaphragms, gears, pistons, rollers, or screws—to draw in fluid into the pump chamber on the suction side and push fluid out of the pump chamber on the discharge side. The suction side has an expanding cavity while the discharge side has a decreasing cavity. This design allows the pump to generate the high pressures needed to move materials with high-viscosities and/or in precise volumes.
How Does a Positive Displacement Pump Work?
Positive displacement pumps rely on the principle of fluid displacement to move fluid from the inlet to the outlet. During each cycle of operation, the rotating or reciprocating component forces a fixed amount of fluid into the expanding cavity and out of the decreasing cavity. The amount of fluid displaced depends on the displacement mechanism employed. The rate of flow will remain constant, regardless of the discharge pressure.
Unlike centrifugal pumps, positive displacement pumps do not have shut-off heads. As a result, they cannot be operated against closed valves on the discharge side. Otherwise, the pump will continue to discharge fluid until the pressure in the discharge line is sufficient enough to damage the line and/or the pump. For this reason, industry professionals often add an internal or external safety or relief valve to the discharge side of positive displacement pumps as a preventative measure.
Types of Positive Displacement Pumps
There are two main classifications of positive displacement pumps: reciprocating pumps and rotary pumps.
Reciprocating Positive Displacement Pumps
Reciprocating pumps rely on components that perform a repetitive linear motion—i.e., up-and-down or back-and-forth—to create the pressure that draws fluid into and pushes fluid out of the pump chamber. Examples of reciprocating pump components include plungers, pistons, and diaphragms. For pumps with pistons or plungers, the suction stroke of the component opens the inlet valve and closes the outlet valve, allowing fluid to enter the pump chamber. The forward stroke of the component closes the inlet valve and opens the outlet valve, allowing fluid to exit the pump chamber. For pumps with diaphragms, the flexible membrane expands and compresses to draw the liquid in and discharge it.
Rotary Positive Displacement Pumps
Rotary pumps utilize components that perform a rotating motion to draw in and push out fluid. Examples of rotary components include gear and screws. The element develops a liquid seal with the pump casing. As a result, it creates suction as it rotates, which pulls fluid into the pump chamber at the suction point and pushes fluid out of the pump chamber at the discharge point.
To learn more about reciprocating and rotary pumps, check out this article. [LINK TO ARTICLE]
Contact the Pump Experts at Glauber Equipment Corporation Today
At Glauber Equipment Corporation, we’ve provided high-quality fluid handling solutions for over 60 years. One of our core product offerings is positive displacement pumps. We maintain a broad selection of equipment from a variety of manufacturers to accommodate the different pumping requirements of our customers. Our experts are available to help identify the best solution for every pumping application.