In the reciprocating piston meter shown schematically in Fig., the reciprocating piston passes the liquid alternately through each end of the cylinder from the inlet to the outlet and also the slide valve which controls the inlet and outlet ports and operates the counter.
Reciprocating Piston Meter
A number of piston operations on a center crank are generally incorporated in this type of meter.
For low flow, the differential pressure is small, for which large diameter pistons and small piston strokes are chosen with minimum of friction. Accuracy of this flow meter is within 0.5%.