Fundamentals of positive displacement pumps

Hydraulic pumps are the heart of every hydraulic system, and they feature many inevitable functions that help improve system performance. Pumps play an important role in converting mechanical energy into useful hydraulic power. You can find different types of hydraulic pumps used in different applications. The pumps are mainly classified into positive displacement pumps and non-positive displacement pumps based on the displacement. Non-positive displacement pumps produce a continuous flow.

However, they did not prevent slippage by providing an internal positive seal. In positive displacement pumps, slip will be minimal. Most hydraulic systems adopt positive displacement pumps instead of non-positive type pumps. Here, we can discuss more details about positive displacement pumps.

Positive displacement pumps are also called constant volume pumps due to their constant speed and flow. These pumps are self-priming and can be designed as non-sealing pumps. Positive displacement pumps are classified into rotary pumps and reciprocating pumps based on the motion of the pumping element. Gear pumps, vane pumps, screw pumps, lobe pumps, etc. are the subcategories of rotary pumps and diaphragm pumps, and piston pumps and plunger pumps are the subcategories of reciprocating pumps.

Where are positive displacement pumps used?

Low initial cost and low operating cost are the advantages of positive displacement pumps over other types. These pumps are suitable for high viscosity applications. The system will have a constant flow regardless of the variable pressure. In short, these pumps are used in applications where precise flow is required. Positive displacement pump applications include high pressure washing, spraying/wiping, water treatment, oil production, irrigation, fuel transfer and injection, beverage dispensers, etc. Apart from these, the chemical, food, healthcare, pharmaceutical and biotech applications industries are reaping the benefits of positive displacement pumps.

How does a positive displacement pump work?

Positive displacement pumps will have two sides, one with an expanding bore for fluid intake and the other with a diminished bore for fluid draining. When the suction side cavity expands, a constant volume of liquid will flow from the tank into the pump. Likewise, the trapped fluid is discharged when the cavity collapses/reduces. This is the working principle of positive displacement pump. We have two major categories of positive displacement pumps, reciprocating and rotary.

Source: Rexroth distributor