Hydraulic motor

pat sublett · Feb 28, 2018

Anyone know the purpose of a case drain on a hydraulic motor and how it is suppose to be connected or if it can be plugged?

Roger in Iowa · Feb 28, 2018

Don't plug it. It should be plumbed to the reservoir. Case drain prevents pressure in the case of the motor from blowing the seal(s) on the shaft.

Brendon-KS · Feb 28, 2018

The need for a drain depends entirely on the type of circuit and the style of motor. All closed-circuit piston motors require the case drain to be plumbed back to tank - otherwise the shaft seal would blow out as soon as the system builds charge pressure. With open-circuit orbital or gear motors the need for a case drain depends on the application and how much back pressure is against the outlet port. For a single motor that returns back to tank the drain line generally isn't required since the case can drain at low pressure into the return side. However, if you have motors in series (the outlet of one feeding the inlet of the next) all motors except for the last one would typically need a drain since the backpressure could exceed what the shaft seals can take.

jm. · Feb 28, 2018

BRANDON HAS IT RIGHT, don,t know how many I have seen try to block on , if the motor came with a third line it needs it.

Bob · Feb 28, 2018

(quoted from post at 11:56:29 02/28/18) The need for a drain depends entirely on the type of circuit and the style of motor. All closed-circuit piston motors require the case drain to be plumbed back to tank - otherwise the shaft seal would blow out as soon as the system builds charge pressure. With open-circuit orbital or gear motors the need for a case drain depends on the application and how much back pressure is against the outlet port. For a single motor that returns back to tank the drain line generally isn't required since the case can drain at low pressure into the return side. However, if you have motors in series (the outlet of one feeding the inlet of the next) all motors except for the last one would typically need a drain since the backpressure could exceed what the shaft seals can take.

Brendon, if the motor is powered from the hydraulic remote ports on a tractor, another issue can come up.

The return flow from the valves for the remote couplings may NOT be just getting dumped in the tank/sump/rearend of the tractor, depending upon the make and model.

I may get forced trough a filter and/or an oil cooler and may be added to the flow in the main pump "charge" circuit, any and all of which can build significant backpressure.

I say if the motor has provision for a case drain USE IT!

Also, (IIRC) some motor manufacturers want the pump to be oriented at or near the top, keeping the pump case full of pressurized oil to lube0 internal parts.bearings, etc..

Hydraulic motor

pat sublett

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Roger in Iowa

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Brendon-KS

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jm.

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Bob

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