SK260-8 air in the hyd. tank

[mkoepf]

I have a Kobelco SK260-8 with around 1040 hrs. I've been having problems keeping a thumb drawed up tight when not in use. The thumb is plumbed in with the auxillary circuit with manual shut off valves. This is the only part of the hydraulics that have been messed with.

Today while trying to load the machine on a trailer i noticed the pump whining loud and the machine will jerk when trying to travel. I pulled the cover to the tank and the oil was really foamy. I've checked the hose clamps on the pump suction and checked the fittings for the pilot pump. Doesnt seem to be any problem there.

I notice while running the machine around that it does not always airrate. The attatchment circuits all operate normal. The travel is where the problem starts. I can hear a loud thud coming from somewhere near the rear of the machine and then the machine will jerk and the pump will whine. I checked pressures on the dash and I stalled out each track individually. With pressure around 5200 psi I can't imagine where air can be drawn into the circuit without spraying oil out. I figure the only place of suction on the system would be the main pump suction and pilot pump. Am I wrong?

Any help is greatly appreciated!

 

[Jam]

Do kobelco use a compressor to charge the hydraulic tank on that excavator?

 

[bobin35]

Did you check the pressure releif valve on top of the tank,has four allen bolts that hold it on after operating push the button on top of the valve to see if there is pressure there you should be able to hear air escaping with engine off.

 

[wildhorse trnr]

Has a service been performed recently?
I have not had foaming happen tome due to oil since the old ATF days, but some of the other field guys I work with have said that the wrong oil can cause foaming in high pressure systems.
Does the unit track well? Did it whine when stalled out?
If it only affects drive, then at least you know where to start looking, does it do it as bad when cold as when warmed up?

 

[mkoepf]

No compressor that I know of. I did check that pressure relief on the tank. It seems to be okay. The problem is intermittant it seems. It tracks straight but once the air gets into the system thats when the pump will whine and have poor performance. It seemed worse when the machine was cold. Its definately in the travel circuit because I can dig no problem until i try to travel.

 

[MR. KOBELCO]

i sent an e-mail response to you.
tomorrow i will look at the hyd scematics and provide further checks you can make.
i really would like to know the hyd oil make and grade

 

[maytag]

If you have foamy oil you probably have aeration problems. A shaft seal on a pump or motor can draw air in and not leak fluid out-you may also have a return line come off in the tank-all lines should be terminated below the fluid level.

Maytag

 

[mkoepf]

I got the problem fixed. The oil level was a little low and below the return filters. Must have been airating due to that fact. The oil level was still well above the suction tube.