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Useful information on Reciprocating Piston Pumps

 

What is a piston pump?

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.

What are the advantages of piston pumps?

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.

What are the disadvantages of conventional piston pumps?

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.

What is a rotating reciprocating piston pump?

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.

What are the advantages of rotating reciprocating piston pumps?

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.

What component materials are available?

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.

What applications are rotating reciprocating piston pumps used for?

Typical applications include:

  • Medical
    Precise dispensing, aspirating, rinsing & mixing systems and for syringe pump replacement in diagnostic, clinical chemistry, dialysis and medical equipment manufacturing.
  • Industrial
    For accurate metering and mixing of paint & pigment additives, catalyst for foundry resins, plating bath regeneration, petroleum additives, photo chemicals, inks, monomers and adhesives.
  • Dispensing Systems
    For dispensing of solvents, UV adhesives, lubricants, reagents, mercury in the manufacture of electronics, pharmaceutical, medical disposables, computers, and calibration equipment.
  • Spraying Systems
    For injection of insecticides, herbicides, and agricultural nutrients. Also used in ULV spray equipment for mosquito control.
  • Environmental & Pollution Control
    For sampling stack gases, ground water & waste water, as well as injection of monomers, polymers, and chemicals for water & waste treatment.
  • Electronics Manufacturing
    For dispensing of ceramic slurries in the manufacture of capacitors and diodes. Also for dispensing of insulating and encapsulating materials used in electric motor manufacture, addition of flux for wave soldering equipment, dispensing of mercury for switch manufacturing, and metering of semiconductor wash & etch solutions.
  • Instrumentation
    For all kinds of precision instruments and monitors including, titrators, TOC, SO2 monitors, chromatographic systems, and humidity control.
  • Pilot Plant
    For research, development, and testing of a wide range of process applications including chemical synthesis, water & waste treatment, power plants, pharmaceutical manufacturing, petroleum refining, and photo finishing.
  • Cosmetic & Hygiene
    Precision dispensing of pigments used in cosmetic colour mixing systems. Also for moisture control and fragrance addition.
  • Battery Manufacturing
    Precision dispensing of electrolytes & slurries into batteries, as well as for lubrication of fine blanking machines used to form and stamp battery components.
  • Automotive
    Hydrogen fuel cell research & development for both the humidification and fuel injection systems. For dispensing insulating and encapsulating coating materials in the manufacture of stators, armatures, and distributors. Also used in instrumentation to verify gasoline octane rating.
  • Food & Dairy
    Sugar coating and polishing, vitamin fortification for milk; addition of flavours, colours, and preservatives, hops for brewing and sanitising agents for aseptic packaging. Also used for sample and reagent fluid control in milk analysers and other food quality control instrumentation.
  • Precision Cleaning
    For dispensing of concentrated cleaning agents used in automated washers for laboratory glassware & mechanical components, as well as the metering of concentrated liquid car wash detergents.

Summary

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.