 If the piston's suction and discharge strokes occur at the same speed and liquid is metered out half the time the pump is working, then the overall metering rate averaged over time equals half the average flow rate during the discharge stroke.Some single-piston pumps may have a constant slow piston motion for discharge and a quick retract motion for refilling the pump head.In such cases, the overall metering rate is practically equal to the pumping rate during the discharge stroke.