Shaft seal, Final drive, Komatsu PC60

[fluidp]

One of my final drives on my excavator is periodically blowing out the shaft seal, which allows hyd. oil into the sun gear case and blows off the outside cover.
When this happened the first time I dissassembled and thought the internal brake was not releasing. I replaced the oring to the brake port and seal and everything was great. about a month later I went out one cool morning and went to travel the machine and the same thing happened.
Took apart, replaced the seal, staightened out the now bent cover and it worked great for a week and did the same thing. The piston motor looks to be in good, clean cond.
I'm getting stumped!! Any suggestions would be appreciated.

 

[hydromech]

Hey...

Repeated shaft seal leakages are most often caused by excess pressure in the drive motor casing.

It's a guess at this stage as I don't even know if the motor has an external drain.

If there is a drain line from the motor casing, it is either too small or it is blocked.

As the motor runs the casing fills with hydraulic oil, if the oil cannot drain back to the oil reservoir at very low pressure, the first sign of trouble is a shaft seal failure.

I saw the same thing on Korean navy minehunter. They had installed a shut off valve in the casing drain. The valve was shut and the casing pressure went upto 300 BAR(4350 PSI). Not bad considering that the shaft seal max pressure was 5 BAR (72.5 PSI). Eventually, the seal housing plate (1/2" thick) was bent allowing oil past the sealing 'O' ring and into the gearbox. The hydraulic oil filled the gearbox and then blew the breather off the top.

If it's not that, I would say there is misalignment in the drive shafts or axial thrust against the seal or the seal housing.

Like I said before only educated guesses at this stage. Any more info available?

Hydromech

 

[kcj]

hydromech has it well covered.
Have seen this issue a lot, especially if there is cold weather plus filter on case drain.

Into gearbox is a problem,. as we have several designs with water glycol hydr fluid and petroleum oil gearbox fluid.

Depending on the pump or gearbox design, you may be able to have dual seals in the pump, one facing each way to separate fluids with a drain to atmosphere in between. That works well, seal the drain hole with a blob of grease to keep dirt out. If either seal leaks, it goes to ground not into the gearbox.

Alternate, some pump drive mfr have sealed cavity around the spline, it can be vented to outside. do the same thing, but using pump with std single seal.

Assuming you have no real choice in the redesign, just trying to keep the existing hardware together, I would focus on case drain pressures. That may require a recording device and transducer, as some fast case spikes may occur during braking or overspeed. Block lift briefly spits major flow to the case, etc. I have seen cast iron cases split and broken in half, yet the spike was so fast and so localized that the shaft seal 6 inches away was not damaged.

kcj

 

[fluidp]

Thanks Gentleman,
Yes there is a case drain on the motor. The case drain from the two final drives and the swing motor all tee together before they go back to tank. I will have to remove the case drain line and check for blockages as I am not having any problems with the other two motors. I will also remove the filters in the tank and make sure they are ok, replace if needed.
Lastly I will install a flow meter on the case line to monitor the case drain flow. Excessive flow could overcome the flow capabilities of the case line and cause resistance. I will post results when I have done the work. Thanks again

 

[wackers]

If a shaft seal fails in a multi motor system I have often known it to be one of the OTHER motors which has a problem.
In other words check every drain INDIVIDUALLY before assuming the motor which blows shaft seals is the one with a fault.
Technical Department SAI (GB) Limited