I assume you are referring to the shaft seal here.

That being the case, then it's worth checking the casing drain line and this again is assuming that you have an piston motor, not a gerotor type.

So, in essence, what I am saying is...we need more information to help you.

Some reasons for failure:
Pressure on the seal too high; return line too small, return goes through a valve that closes when the motor is valved off (cylinfer valve instead of a motor valve), blocked case drain if one exists, no case drain if one is required.
Shaft defect under the seal.
Seal gland bore defect allowing leak past the seal OD.
Wrong seal.
Improperly installed seal.

Ted

Hi Everyone
Thanks for your replies, I am sorry for responding late. Pump details as below
Motor:1
Make: Hydrocar
Model: 200FZ0043DS
Type: Gear

Motor:2
Make: OMFB
Model: HDS 47 D (R)
Type: Piston

The OP mentioned a hydraulic motor application. The Hydrocar part no. is an external gear pump designed for clockwise shaft rotation. Using it as a motor may cause problems depending on the specific design details. For example, external gear pumps sometimes use pressure compensation plates that are only designed to work for a pump with a specific direction of rotation. Check with the manufacturer to see if this pump can be used as a motor.

Assuming the RPM rating of motor is match with the pump rating.
What's the life of the pump?
has anyone checked the pump shaft for any defect?
any excessive vibration during operation?
What about the bearing? is it still ok?
System is clean? Meaning flushing found no contaminant?

Hi tbuelna, thanks for a different view, I didn't check this compatibility till now, I will check and get the information.
@ BEMPE16524: it is 2years old, and there is no unusual vibrations during operation. I inspected the shaft while it has some thermal stress marks (blue and black) on the edges and root of the rotor. We flushed the system and there was no contamination observed.

Oil leak starts immediately when we start the operation.

Check the seal gland for damage caused during seal removal and/or installation.

Ted

Quote (oswald88 (Mechanical) (OP) 19 Oct 16 08:36 Hi tbuelna, thanks for a different view, I didn't check this compatibility till now, I will check and get the information. @ BEMPE16524: it is 2years old, and there is no unusual vibrations during operation. I inspected the shaft while it has some thermal stress marks (blue and black) on the edges and root of the rotor. We flushed the system and there was no contamination observed. Oil leak starts immediately when we start the operation. )

Have you tried change the pump?

@BEMPE16524: Yes I tried with another motor, it is working, not I did some machining to fit the right love-joy coupling. Hopefully this motor should work. Will update you if it is successful.

sorry i mean 'change the motor'. good luck.