Losses in hydrostatic input/output elements mainly caused by friction forces — which may depend on rotation speed, pressure or velocity — and by flow losses. The resulting loss torques are M c = constant losses due to inaccurate assembly, M Δp = losses due to pressure difference (friction and jamming forces), M ν = losses due to fluid friction and M ρ = flow losses. These give a total loss torque M V
![93e25face7ffa4b3287a7931583a3baba2eb57b9 hydraulischmechanischerwirkungsgrad_01.gif](/fileadmin/smc/files/93e25face7ffa4b3287a7931583a3baba2eb57b9.gif)
With hydraulic pumps, this loss torque must also be counted in addition to the theoretical torque (Figure H 11):
![ee0db4ce446676172fe55bce118831c7ad08254e hydraulischmechanischerwirkungsgrad_02](/fileadmin/smc/files/ee0db4ce446676172fe55bce118831c7ad08254e.gif)
which in turn gives
![319ff657ae3f661f0e999ede24f0c4e9a440c265 hydraulischmechanischerwirkungsgrad_03](/fileadmin/smc/files/319ff657ae3f661f0e999ede24f0c4e9a440c265.gif)
With hydraulic motors by contrast, the usable torque is reduced by the loss torque (Figure H 12):
![bfe777fa92d0c4785f9025fb4e45df30ba2aa474 hydraulischmechanischerwirkungsgrad_04](/fileadmin/smc/files/bfe777fa92d0c4785f9025fb4e45df30ba2aa474.gif)
which gives
![cd584df238a4bd877e25ce8db123f36e26ac61a2 hydraulischmechanischerwirkungsgrad_05](/fileadmin/smc/files/cd584df238a4bd877e25ce8db123f36e26ac61a2.gif)
With hydraulic cylinders, most friction is caused by the seal (F Re); which in this case gives
![11b511ac2b76f9f91e933fb885d91d582e59bece hydraulischmechanischerwirkungsgrad_06](/fileadmin/smc/files/11b511ac2b76f9f91e933fb885d91d582e59bece.gif)
Total efficiency, power losses
![c2a4e0a89788dec9e72224f0ed1e608937d72ded 0001_hydraulischmechanischerwirkungsgrad](/fileadmin/smc/files/c2a4e0a89788dec9e72224f0ed1e608937d72ded.gif)
Figure H 11: Drive and loss torque for hydraulic pumps
![666720b7dcef1e845587df58daaec01576d700ca 0002_hydraulischmechanischerwirkungsgrad](/fileadmin/smc/files/666720b7dcef1e845587df58daaec01576d700ca.gif)
Figure H 12: Drive and loss torque for hydraulic motors