Hydromechanical efficiency

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

With hydraulic pumps, this loss torque must also be counted in addition to the theoretical torque (Figure H 11):

which in turn gives

With hydraulic motors by contrast, the usable torque is reduced by the loss torque (Figure H 12):

which gives

With hydraulic cylinders, most friction is caused by the seal (F Re); which in this case gives

Total efficiency, power losses

Figure H 11: Drive and loss torque for hydraulic pumps

Figure H 12: Drive and loss torque for hydraulic motors