What is a hydraulic motor?

Through this page I tried to make a short description about hydraulic motor although the subject is well known. If google it sure it will be found some good information about it.

Even though the subject is widely know I will show more deeply information from sources where I learned and understand this hydraulic component.

For more practical information about hydraulics check regularly Marine Hydraulics Tips

I will present here the radial piston motor because I know this type of motor. I serviced this kind of motor on board, bench tested and assembled in the workshop. From practical side I am familiar with this type of hydraulic motor.

Characteristic of a motor is to converts hydraulic energy –  from a hydraulic pump – into mechanical energy.

Radial piston motor can work at low speed between 1-5 rpm with very high drive force where the working pressure is high means when heavy loads. Are able of operating at very high speeds of 12 000 rpm and also pressures up to 350 kg/cm² (4980 psi approx.). Large piston motors are able of delivering flows up to 1500 LPM.

Type of hydraulic piston motor

Is the most reliable type and consequently the most used hydraulic motor.

The motor pistons are fitted in a star connection, perpendicular to the shaft. The pistons provides a linear motion and the conversion in rotary motion is achieved by and excentric disk. A disk whose axis is off center of stator axis.

Overhauling hydraulic piston motor

The motor shaft fitted with the excentric disk. A handgrip separate ring is installed or fitted around the disk and which will be move up and down when the shaft is rotating.

During the pistons stroke each one pushes away the excentric from it causing the shaft of motor to turn.

Only the piston block rotates in the radial piston motor. Rotary motion is generated by pistons which are push outward or extend and push against the outer wall which has the shape of cam ring.

Large number of pistons produce and build big forces. 

The pistons are fitted in a piston block in an odd and even number. The piston motor design usually involves fitting an odd number of pistons. If one piston may get blocked the other ones receives the fluid as the ones discharging the fluid.On the contrary, with even number of pistons and one getting blocked, there would be one more piston either receiving or discharging the fluid leading to speed and torque pulsations or vibrations.

What is a hydraulic motor?
  • Most reliable type and consequently the most used hydraulic motor.
  • The motor pistons are fitted in a star connection, perpendicular to the shaft.
  • The motor shaft fitted with the excentric disk whose axis is off center of stator axis.
  • Large number of pistons produce and build big forces. 
  • The piston motor design usually involves fitting an odd number of pistons.

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