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What Are Important Things You Should Know About Hydraulic Motors?

This section within a hydraulic system is a rotary actuator that converts hydraulic fluid energy into mechanical power. It works in unison with another component called a hydraulic pump that converts this mechanical energy into hydraulic power.

There are three most common types for hydraulic motors:

  • Gear,
  • Vane,
  • Piston.

They come in a variety of styles with the least common being gerotor and gerolor motors.

Hydraulic Motor Displacement

This hydraulic system component can either be at a fixed or variable displacement, whilst operating either bi-directionally or uni-directionaly.

  • Fixed-displacement hydraulic motors drive at a constant speed whilst a continuous input flow and torque is provided by it.
  • Variable - displacement motors change their displacement to provide variable flow rates, torque and speed within the hydraulic system.

Hydraulic Motor Torque

Toque for this hydraulic component is expressed in in.-lb or ft-lb (Nm) and there are three different types of torque.

  • Breakaway - this is normally used to define the minimum toque required to start an hydraulic motor without a load. This measurement is based on the internal friction in the motor and is the initial force required to start the hydraulic motor system.
  • Running - this torque produces enough energy to keep the motor with and without a load running.
  • Starting - this is very much like the breakaway torque described above, but is used for starting hydraulic motors that are under load. It is a combination of energy that is required to start the under load motor and the internal motor friction.
  • The ratio of actual torque to theoretical torque gives us the mechanical efficiency of a hydraulic motor.

Defining An Hydraulic Motor’s Internal Volume

This is not done by looking at its displacement, but by the oil level that is introduced into the motor during an output shaft revolution. When measured at either in.3/rev or cc/rv it is the hydraulic motor’s volume.

Calculated by:

  • Adding the volumes of the motor chambers,


  • By rotating the motor’s shaft one turn and collecting the oil manually, then measure it.

Measuring An Hydraulic Motor Flow Rate

This calculation is the oil volume that is introduced into the hydraulic motor per unit of time for a continuous output speed and is measured in liters per minute (lpm) or gallons per minute (gpm).

Calculated by:

  • Multiplying the hydraulic motor displacement with the running speed,


  • By using a flowmeter,


  • By rotating the motor’s shaft one turn and collecting the hydraulic fluid manually.

With all this in mind you are ready to venture into the world of hydraulic motors and there is no company with a better selection than Flowfit!

To find your hydraulic motor check out our fantastic range online, and for further advice on all the hydraulic components we stock here at Flowfit contact our friendly team today.

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