Fluid Power Journal

Rotating Stage’s Hydraulic Motor Keeps Leaking

A large entertainment stage is rotated by a Geroler type hydraulic motor shown on the circuit. The regenerative center position on the directional valve eliminated a sudden jerk when first started since both ports were already pressurized. The pilot operated directional valve also had a smaller pilot pressure orifice installed to slow down the shifting speed softening the acceleration phase of the start cycle.

The problem they were complaining about was the big puddle of oil leaking out from under the stage every couple of months that required replacing the hydraulic motors that were leaking out through the shaft seal. They changed to a different Geroler brand motor and still suffered the same failure.

Any idea what the problem could be?

See the Solution

A large number, more that 50% would be my guess, of all Geroler type motor do not use a case drain. Typically, the output port of the motors goes back to tank with little back pressure. The case drainage leaks into this low-pressure port and keeps the case pressure at a low level greatly reducing the wear on the shaft seals. The regenerative spool and meter out flow controls require an external case drain since both ports see high pressure at the same time.

By Robert Sheaf, CFPAI/AJPP, CFPE, CFPS, CFPECS, CFPMT, CFPMIP, CFPMMH, CFPMIH, CFPMM, CFC Industrial Training

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3 thoughts on “Rotating Stage’s Hydraulic Motor Keeps Leaking

  1. Sean Neitzel, CFPS

    The oil is leaking out of the geroler motor shaft seal when the pump is turned on and the directional control valve is in it’s neutral position. Both ports of the motor are pressurized to the pump compensator setting of 2600 psi, which is much too great for the shaft seal hence the leakage. Typically a geroler type motor would have a case drain port which should be plumbed back to tank (low restriction) in a bi-directional application such as this, which would solve the shaft seal leakage.

    Reply
  2. Dave Briggs

    I’m surprised it took a couple month, likely starting leaking from the motor shaft seal shortly after install. Pressurizing both ports of the motor with no external case drain caused a high internal pressure situation resulting in a very premature failure of the motor shaft seal. Likely extruded the seal lips or pushed the whole seal out of the can bore. Plumb a case drain, unrestricted back to tank and problem solved.

    Reply

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