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Oscillating Piston Flow Meters Working Principle

Oscillating piston meters use a precision-machined chamber containing a cylindrical piston that oscillates as liquid flows. The piston’s central shaft is constrained to run in a circular groove in the chamber, resulting in an off-center rotating motion as the liquid sequentially enters and exits compartments machined into the underside of the piston. Since the volume of the compartments are known, the amount of liquid metered per revolution can be calculated accurately.

Oscillating Piston Flow Meters Animation

Liquid enters a precision-machined chamber containing an oscillating (rotating) piston. The position of the piston divides the chamber into compartments containing an exact volume. Liquid pressure drives the piston to oscillate and rotate on its center hub. The movements of the hub are sensed through the flowmeter wall by a follower magnet. Each revolution of the piston hub is equivalent to a fixed volume of fluid, which is indicated as flow by an indicator/totalizer. Close clearances between the piston and the chamber ensure minimum liquid slip for highly accurate and repeatable flow measurement of each volume cycle.


  • High accuracy and repeatability.
  • Only one moving part to cause wear.
  • Can be made of materials to ensure sanitary needs of food and beverage processing.


  • Can only be used with relatively clean liquids.

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