Pumps with a finite number of displacement units (pistons, vanes, teeth) deliver a flow rate that fluctuates around an average value due to the periodic change between the suction and pressure phase. The difference between the largest value and the average value is larger, the smaller the number of displacement units (Figure F 27).
Here piston pumps with an even number of pistons have double delivery flow pulsation (select odd number of pistons!) If the delivery flow pulsation is not damped (e.g. by an accumulator or a piece of hose), it can become apparent at the actuator in the form of discontinuous movement. In addition, it causes in the pump and in the hydraulic fluid a pressure pulsation.
Figure F 27: Delivery flow pulsation for different numbers of pistons