Hydraulic Pumps and Motor Sizing

Motor size versus flow rate, shaft torque, shaft power and hydraulic power

Equations for hydraulic pumps:

Flow rate

Q = D n / 1000                                     (1)


Q = flow rate (l/min)

D = displacement of piston (cm3/rev) 

n = revolutions (rpm)

  • rev = revolution
  • rpm = revolution per minute

Shaft Torque

T = D p / 20 π                               (2)


T = torque (Nm)

p = pressure (bar)

Shaft Power 

Ps = T n / 9554                            (3)


Ps = shaft power (kW)

Hydraulic Power

Ph = Q p / 600                           (4) 


Ph = hydraulic power (kW)

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