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):
![36f146e389be248bbc47ea2a344af2d3623098ac verlusteinverdraengermaschinen_01.gif](/fileadmin/smc/files/36f146e389be248bbc47ea2a344af2d3623098ac.gif)
The effective drive torque M 1eff on the pump shaft is greater than the theoretical drive torque M 1th by the moment losses M 1V (Figure V 13 a):
![28b4e3164091fd491010953773e652fa5fc7edac verlusteinverdraengermaschinen_02](/fileadmin/smc/files/28b4e3164091fd491010953773e652fa5fc7edac.gif)
In the case of the motor, the effective displacement flow Q 2eff is formed by the sum of the theoretical displacement flow Q 2th and the leaked oil Q 2L:
![d0d53d049360776f883ea829b3b7e2e320a1d596 verlusteinverdraengermaschinen_03](/fileadmin/smc/files/d0d53d049360776f883ea829b3b7e2e320a1d596.gif)
The moment created M 2eff is M 2v smaller than the theoretical (hydraulic) moment M 2th (b):
![511e11875f93482217289d1cf3171d5dca5a1861 verlusteinverdraengermaschinen_04](/fileadmin/smc/files/511e11875f93482217289d1cf3171d5dca5a1861.gif)
![f94e0167c56a040f0ed324d1170fb77bce49fc7b 0001_verlusteinverdraengermaschinen](/fileadmin/smc/files/f94e0167c56a040f0ed324d1170fb77bce49fc7b.gif)
Figure V 13: Moment losses in hydraulic pumps (a) and (b) hydraulic motors