The decision to opt for a positive displacement pump (PDP) over the other varying kinds of pumps isn’t always a clear one. Each pump features a truly different behaviour and if unfamiliar with them, it can turn out challenging to understand how this type of pump might fit into your process.
These pumps are a much more efficient option than other kinds of pumps in similar situations. If any of the applications or conditions listed below happen to be in your process, then you should most probably use this type of pump.
- Low flow
Frequently, centrifugal pumps are run off their BEP when lower flows are needed, much to the detriment of the pumps. If you have gone through resources detailing how the curve of these pumps can be read, then you will understand that running them off their BEP could end in excessive consumption of energy, ruin to the pump, and all-round poor performance.
A PDP, nevertheless, is well fitted for such conditions, offering constant fluid flow at a specific pump speed. If you are attempting to get the flow or pressure you require by operating centrifugal pumps off their BEP (best efficiency point), a PDP might then turn out to be a much better option.
- Shear-sensitive liquids
Generally, centrifugal pumps operate at much higher speeds in comparison to their PDP counterparts. The higher speeds could shear fluids, making them a poor option for fluids like latex paint and tomato paste. Any of the positive displacement pump types, operating at much lower speeds could be a lot gentler on products and are typically favoured in these kinds of applications.
- High viscosity
Centrifugal pumps have problems when it comes to pumping fluids that are viscous, becoming quite inefficient even at the most modest of levels. On the other hand, PDPs do not have any issues when it comes to moving thick fluids.
- Metering
PDPs are surely a most ideal option for metering applications. They effectively deliver consistent flow, thus enabling them to meet all process requirements quite easily. Some of the most common kinds of PDPs that are utilised for metering include;
- Gear
- Plunger
- Peristatic
- Diaphragm
- Piston
- High-pressure requirements
PDPs are truly excellent for all applications that demand truly high pressure, with some models offering as much as 1,000psi (2,300ft). As a result of the design of PDPs, nevertheless, if they are kept operating against a discharge valve that is closed, they will keep on building pressure till the pump gets damaged, the line gets bursts or even both.
- Multi-phase flow
A constant liquid source is a centrifugal requirement, but unluckily, not all processes offer such constant sources. If there’s not enough liquid, a gas bubble is then formed within the suction and brings about the loss of prime (pump ceases to pump). Conversely, PDPs can handle high percentages of gas or air entrainment.
In conclusion, a positive displacement pump and other varying pumps behave quite differently from one another. Excellent knowledge of their varied behaviours can see you surely opting for the most appropriate pump for your process or application. Contact the foremost experts if you need further clarifications.
