The heart of every hydraulic system, the hydraulic pumps have many inevitable duties that help to improve system performance. Pumps play an important role in converting mechanical energy to useful hydraulic energy. You can find a variety of hydraulic pumps types used for varying applications. Pumps are mainly classified into positive displacement pumps and non-positive displacement pumps based on displacement. Non-positive displacement pumps produce a continuous flow. But, they did not prevent slippage by providing an internal, positive seal. In positive displacement pumps, slippage will be negligible. Most of the hydraulic systems will adopt positive displacement pumps than non-positive type pumps. Here, we can discuss more details on positive displacement pumps.
Positive displacement pumps are also called constant volume pumps because of their constant speed and flow rate. These pumps are self-priming and can be designed as a sealless pump. The positive displacement pumps are classified into rotary 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, piston pumps and plunger pumps are the subcategories of reciprocating pumps.
Where are positive displacement pumps used?
Lower initial cost and operating cost are the advantages of positive displacement pumps over other types. These pumps are suitable for high viscosity applications. The system will get constant flow irrespective of varying pressure. In short, these pumps are used in applications that require precise flow.Positive displacement pump applications include high-pressure washing, spraying/cleaning, water treatments, oil production, irrigation, fuel transfer and injections, drinks dispensers, etc. Other than these, chemical and food industries, sanitary, pharmaceutical, and biotechnology applications utilize the benefits of positive displacement pumps.
How does a positive displacement pump work?
The positive displacement pumps will have two sides, one with an expanding cavity to intake fluid and other with a decreasing cavity to discharge fluid. When the suction side cavity expands, a fixed volume of fluid will flow from the reservoir to the pump. Similarly, the trapped fluid discharges when the cavity collapses/reduces. This is the positive displacement pump working principle. We have two major categories of positive displacement pumps, reciprocating and rotary.
Also, Read: How Hydraulic Pump Works
What are the differences between these positive displacement pumps working?
The working of the reciprocating pump is based on the back and forth repeated movement of piston, diaphragm or plunger. The rotary pumps work based on the rotating motion of cogs or gears. In reciprocating pumps, the flow is dependent on the number of piston strokes. While in rotary pumps, the flow will depend on the speed of rotation of gears. The positive displacement pumps use a constant volume of fluid for its operation. So, the performance of these pumps can be indicated as a relation between flow rate and pump head. The positive displacement pump curve will help to calculate the ideal performance, actual performance and slippage due to leakage.
Can positive displacement pumps run dry?
Not all, but some types like piston pumps and diaphragm pumps can be operated under dry conditions for a long period. Others can be operated for a short time, only if the impeller or gears are constructed using self-lubricating material like Rython.