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Liquid transfer with low-pressure pulsation

10 May 2021

Diaphragm pumps offer many advantages to users, such as durability, dry-running safety, and suitability for transporting abrasive liquids. However, diaphragm liquid pumps with only one working diaphragm may sometimes cause significant pressure pulsation.

High-pressure peaks may not only result in a decreased service life of the pump and its components, but may also limit the system efficiency.

KNF is always looking to improve existing pumps and to develop new pump technologies. Therefore, the company has developed the low-pulsation FP pump series in response to market needs.

Stop-and-go traffic – or: why pressure pulsation occurs

Liquid diaphragm pumps belong to the so-called volumetric displacement pumps category. The flow rate is generated by periodic volume changes inside the diaphragm chamber. Due to hydraulic resistances between the diaphragm chamber and the final load, the volume pulse turns into a pressure pulse. Hydraulic resistances like this can be found inside the pump (e.g. valves), but also as components inside the customer system (tubes, filters, constrictions, branches, etc.). You can think of this as being similar to the flow of traffic in a cinema parking garage: after the end of a movie, many visitors are leaving the parking garage intermittently. If there were no barriers at the exit, the traffic would flow without backup (pressure). However, due to obstacles such as a single-lane exit road, the volume pulse (many people leaving the cinema simultaneously) turns into a pressure pulse (backup of cars). After all the cars have left the parking garage, it gets quiet until the end of the next movie (analogous to the suction stroke of the diaphragm pump).

For some applications or areas of use, the pressure pulsation can be significantly reduced by interconnecting several diaphragms in parallel, or by using dampeners.

Why pressure pulsation should be avoided

In many pump applications, pressure pulsation or volume pulsation is not desired. Especially in the inkjet area, pressure fluctuations affect the quality of the printed image. On top of this, small tube diameters are frequently used in this application, which results in high-pressure losses. High-pressure pulsation reduces the lifetime of system components and generates strong vibrations and, thus, a higher noise level. This may also lead to a foaming of the liquid and, in the worst case, even cause damage to the transferred medium. Unfortunately, nearly all volumetric pumps, such as peristaltic, gear, piston or diaphragm pumps generate some pulsation.

KNF has developed solutions for low-pulsation liquid transfer to enable optimal application functionality: the FP pump series is based on two different operating principles.

Read the full article in the May issue of DPA

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