How does the M series positive displacement meter measure the flow rate?
The M series positive displacement meter measures flow rate by using its synchronized rotors (two bladed displacement rotors + one central blocking rotor) to trap fixed volumes of liquid as they rotate within the meter's cylindrical bores.
As liquid enters the meter, it drives the displacement rotors to turn (in sync with the blocking rotor, which maintains a capillary seal between upstream/downstream liquid). Each full rotation of the displacement rotors displaces a precise, fixed volume of liquid. The meter then calculates flow rate by counting the number of rotor rotations (via timing gears: the blocking rotor gear-with twice the teeth of displacement rotor gears-rotates at half their RPM, ensuring synchronized movement) and converting this rotation count to volume over time.
At its core, the M series meter operates on the positive displacement principle: it physically traps discrete, fixed volumes of liquid as they pass through the meter, then counts how many of these volumes are displaced over time to calculate flow rate. The meter's housing contains three cylindrical bores: two for the bladed displacement rotors and one for the central blocking rotor. These three rotors turn in a perfectly synchronized relationship (enabled by timing gears at the end of each rotor shaft) with no metal-to-metal contact, which minimizes wear and ensures consistent performance.
When liquid enters the meter's upstream side, it applies pressure to the bladed displacement rotors, forcing them to rotate. As each displacement rotor turns, its blades move alternately through the half-cylinder bores of the meter element. With each rotation, the rotors "capture" a specific, calibrated volume of liquid in the space between their blades and the meter's inner walls. The central blocking rotor plays a key role here: as it rotates within its own bore, it maintains a continuous capillary seal between the unmetered upstream liquid and the metered downstream liquid. This seal prevents liquid from bypassing the displacement rotors (which would skew measurements) and ensures that only the trapped fixed volume moves from the upstream to downstream side per rotor segment.
The synchronization of the rotors is governed by timing gears attached to the end of each rotor shaft. The blocking rotor's gear has twice as many teeth as the gears on the displacement rotors; this means the blocking rotor rotates at half the RPM of the displacement rotors. This precise gear ratio ensures that the displacement rotors and blocking rotor move in perfect harmony: the displacement rotors trap liquid as they turn, while the blocking rotor adjusts its position to maintain the seal and clear the path for the next trapped volume-eliminating gaps or overlaps that could affect measurement accuracy.
To translate this mechanical movement into a flow rate reading, the meter tracks the number of rotations of the displacement rotors (or the blocking rotor, adjusted for its slower speed). Since each full rotation of the displacement rotors corresponds to a known, fixed volume of liquid (calibrated during manufacturing), multiplying the number of rotations by this fixed volume gives the total volume of liquid that has passed through the meter. Dividing this total volume by the time elapsed during the measurement period yields the flow rate (e.g., liters per minute or gallons per hour).
This design ensures the M series meter delivers reliable flow rate measurements across a wide range of applications-from liquid transfer to process control-even for fluids with varying viscosities, as the positive displacement mechanism is less sensitive to flow turbulence than other meter types (e.g., turbine meters). The lack of metal-to-metal contact also means the meter requires minimal maintenance, while the capillary seal maintains accuracy by preventing slippage of liquid between the upstream and downstream sections. In short, the M series meter's flow rate measurement relies on the precise, repeatable trapping of fixed liquid volumes via synchronized rotors, with gear-driven timing and a sealing mechanism that guarantees each trapped volume is accurately counted and converted to flow rate data.
