Positive Displacement

The working principle of a Positive Displacement (PD) flowmeter relies on the continuous physical separation of the fluid stream into discrete, precisely measured volumetric segments. As fluid enters the meter, it encounters internal moving components—such as oscillating pistons, rotating gears, or sliding vanes—that form a tight seal against the chamber walls, trapping a known volume of liquid or gas. The pressure of the flowing fluid forces these components to move, “displacing” the trapped volume from the inlet to the outlet; each full cycle or rotation corresponds to a specific volume of fluid. By counting the number of these cycles via a mechanical register or electronic pulse, the meter determines the total volume and flow rate with high repeatability, making it an ideal “mechanical meter” for high-viscosity fluids where flow profiles are often inconsistent.