A piston pump is a type of positive displacement pump in which fluid is moved by the repeated back-and-forth movement (strokes) of a piston. These cycles are called reciprocation. The strokes of a conventional piston pump are shown in Figure 1. During the suction phase, the piston opens an inlet valve, closes the outlet valve and draws fluid into the piston chamber. As the motion of the piston reverses, the inlet valve, now under pressure, is closed and the outlet valve opens allowing the fluid contained in the piston chamber to be discharged.
The repeatable and predictable action of piston pumps makes them ideal for applications where accurate metering or dosing is required. By altering the stroke rate or length it is possible to provide measured quantities of the pumped fluid. Flow is independent of feed pressure and the low internal velocity makes piston pumps ideal for handling shear-sensitive fluids.
Piston pumps can handle high viscosity fluids such as oils and slurries at high pressures.
Conventional piston pumps are prone to leakage because it is difficult to achieve a good seal around the piston, particularly with a low viscosity feed because of the high pressures generated during the compression phase. Valves and seals require regular maintainance and replacement particularly when used with feeds containing solids or slurries.
As in conventional piston pumps, the pumping function in a rotating reciprocating piston pump is achieved by the cyclic, back and forth, action of the piston. However, the piston also rotates within a ceramic liner, alternately aligning a cut-out slot on the piston with the inlet and outlet ports of the pump. Only one port is open to the piston chamber at any time and at no point are the ports connected. Each rotation cycle completes one suction and one discharge phase (see Figure 2). This mechanism eliminates the need for seals and inlet and outlet valves: the major causes of maintenance issues in conventional piston pumps. Pumps of this type can maintain high dosing precision for millions of cycles with flow rates from a few microlitres to 4600 ml/min with discharge pressures up to 200 psig. The pumps are self-priming and can pump in either direction. The piston stroke length determines the dosing volume and, in turn, the flow rate.
In comparison to conventional piston pumps, or syringe dispensing and peristaltic pump systems, there are no valves to leak or clog, reducing maintenance issues. There is a simple 2-port configuration and only one moving part – the ceramic piston. The materials of construction are resistant to particles or slurries and unaffected by motor speed. Output does not change more than ± 1% of the set value and a rotating reciprocating piston pump has low power consumption. Combined pump and drive systems are fully compatible with industry-standard analogue and/or digital communication protocols for automated process control.
Rotating reciprocating piston pumps consist of three wetted components: the piston, cylinder case and cylinder liner. Pistons can be constructed from ceramic (alumina), stainless steel, or zirconia. The cylinder case can be made from PVDF (fluorocarbon), 316 stainless steel, Teflon® (PTFE) or Tefzel® (ETFE). The cylinder liner is available in ceramic (alumina), or sintered carbon.
Pump heads are available for accurately handling fluid streams in sanitary applications (food, dairy, brewery, pharmaceutical & biotech applications). These have no internal threads or blind holes to harbour bacterial growth and are easily dismantled for scrubbing, brushing, & sterilisation. Wetted parts made from 316 stainless steel and Teflon® are highly resistant to chemical and biological attack.
Typical applications include:
The pumping action in a rotating reciprocating piston pump is achieved by the cyclic, back and forth, action of a piston. However, the piston also rotates within a ceramic liner, alternately aligning a cut-out slot on the piston with the inlet and outlet ports of the pump. This mechanism, with one moving part, eliminates the need for seals and conventional check valves at the inlet and outlet – the major causes of maintenance issues in conventional piston pumps. The piston stroke length controls the dosing volume and flow rate. This can be adjusted, even during operation. Rotating reciprocating piston pumps are used in many applications requiring precise dispensing and automation.
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