Relative delivery fluctuation δ

Fluctuations of the flow rate of hydrostatic displacement machines resulting from the final number of displacement units and their sinusoidal working patterns (Table U 3). It is expressed in the form of flow rate pulsations (flow rate pulsations caused by the pump kinematics). The relative delivery fluctuation is calculated as the difference between the maximum and minimum flow rate, in relation to the average flow rate:

Its size depends on the construction design of the pump and the number of displacement elements. In addition, in the case of piston pumps with an even number of pistons, δ is around twice as high as in the case of an uneven number.

The kinematic delivery flow based on the relative delivery function is also responsible for moment fluctuations in hydraulic motors around the average torque (Figure U 16). This effect becomes clearer at low rotation speeds. It defines the lower possible rotation speed of a hydraulic motor, which can remain beneath it at certain angles.

Table U 3: Kinematic relative delivery flow of different pumps a) gear pumps; b) piston pumps

Figure U 16: Torque fluctuations in an axial piston pump