Losses in hydrostatic displacement machines are comprised of the leakage losses in the displacement elements and the control surfaces (summarised in the volumetric efficiency η Vol) and moment losses, which are summarised in the hydromechanical efficiency η hm.
The effective delivery flow Q 1eff (flow rate at the pressure connection) of a pump is smaller than the theoretical drive rotation speed Q 1th by the leakage losses Q 1L (product of drive speed and displacement volume):