How do piston pumps work?

Piston, or plunger pumps are a reciprocating positive displacement pump type. This means that they operate through the displacement of fluid through a reciprocal pumping action.

Understanding the technology

Piston, or plunger pumps are a reciprocating positive displacement pump type. This means that they operate through the displacement of fluid through a reciprocal pumping action. A set volume of fluid is drawn into an enclosed chamber where it is held until being discharged at a pressure determined by the application. Also known as plunger pumps, piston pumps are typical in industrial applications and laboratory environments where accurate and repeatable performances are essential. The pump design supports the delivery of these performances even at high pressures.

piston and plunger pump

The different types of piston pumps

There are two main types of piston pump types—valve and valveless. Valved piston pump—as the name suggests— rely on a number of check valves to operate. Ball valves sit at the inlet and outlet to control the flow, for example. 

The pump technology is essentially a mixture of the principles applied in both diaphragm and syringe pump technologies. The pump has a central cavity where fluid is drawn in and out by the movement of a piston. This movement has a direct influence over performance, though this is limited by the power of the drive motor and the rpm the pump can operate.

Both flow and pressure are affected by the size of the pump. The smaller the area of the pump's cavity, the greater the pressure and lower the flow rate—much like a syringe pump. Conversely, a pump cavity with a larger cavity volume will increase the flow rate but decrease the pressure. 

Valveless piston pumps do not require valves. The immediate benefit is that there are less moving parts to wear or break, improving both service life and chemical compatibility. The technology relies on the movement of a piston with a cutaway that serves to block the inlet and outlet as it moves forward and backwards in the chamber. 

This pumping action helps to deliver high accuracy and repeatability over long periods of operation. The pump also benefits from having a good control and steady flow rates, with medium viscous fluids. They keep a good flow rate with varying viscosities and can handle medium to high pressures.

Complications of the design

Piston pumps are expensive to maintain, requiring disassembly for cleaning, which can still be difficult to achieve properly. The result is that there is an increased risk of contamination. This is a significant disadvantage in critical environments such as the laboratory, where sterility assurances are essential.

The valves in a piston pump are prone to clogging which makes them a poor choice for particulates handling. To protect the valves, piston pumps often require ancillary equipment such as strainers, particularly when they are tasked to handle viscous material. The valves also increase the number of moving parts, such as foot valves that are needed to maintain prime.

Peristaltic pump advantages in abrasive handling duties

Fluid in a WMFTS peristaltic pump passes through an abrasive-resistant tube or hose. There are no other components in the fluid path. Changing a hose or tube can be done in minutes, without special tools or skilled labour and with the pump remaining in-situ.

WMFTS pumps features include

  • Pump viscous and abrasive fluids with linear flows
  • Simple to operate and inexpensive to maintain
  • No ancillaries needed for installation or running
  • Superior flow stability and metering accuracy

The world leader in peristaltic pump manufacture and associated fluid path technologies

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