Komatsu PC290-11 Hydraulic issues

[lilbunk480]

Running into hydraulic issues on a Komatsu PC290-11 S/N A28630. Relief pressure for the bucket is only running 2200 PSI each way, arm out is at 3500, arm in at 3800, boom down at 2800. Boom up is at 5200 where it should be so I know the main relief shouldn't be a problem. The power max function is only working to increase pressure on boom up. The swing and travel pressures are also correct. PPC pressure for all functions is reading 470 psi. I also noticed the pumps only merge when on boom up relief. I switched the boom up and down pressure comp valves around and noticed no change. When pinning each track I'm getting 5600 psi so pumps should be good. Is there any way to adjust relief pressures for individual functions on this machine? I'm not having much luck in the service manual. TAI

 

[John C.]

The system is load sensing. The main reliefs are only in place when an external force is applied while a function is moving. An example would be a tree falling over the boom when the boom is being lifted. Have you checked for codes in your monitor panel? How many hours are on the machine? What kind of maintenance has been done on the hydraulic system and how many hours since that was done? Have you checked the hydraulic filters and pump suction strainer?

 

[lilbunk480]

No codes even in the service menu. Just got this machine with 400 hrs on it and a blown motor. Motor is fixed now. All filters have been replaced and the old ones were clean.

 

[John C.]

Was the motor removed from the machine and the pump left in place or was the pump and engine removed together. Is that 400 total machine operating hours?
I'll separate out the symptoms that your state. Problem circuits are bucket open and close, arm out and in and boom down. The rest of the functions appear to be working correctly.
As I recall the pump merge function works when traveling and using one of the other circuits at the same time. Power max function works all the time for the travel functions. Putting the swing parking brake function on in the older models put the power max function on all the time. The power max function used to be the only function that would bring the main relief pressures into play.
So you can check that. Is this all true?

 

[lilbunk480]

Yes 400 total machine hours, pump and engine were removed together. Your symptoms are correct. I have dealer telling me there’s a way to adjust pressure for each function separately but I’ve yet to hear the specifics on that and can’t find a procedure in the service manual.

 

[Steve Frazier]

I'm by no means an experienced mechanic, especially with this machine, but processing what I've read here is it possible the valves for the weak circuits are either blowing by or not opening completely?

 

[John C.]

I think you are correct Steve. The question is what components are causing the problem.

Pressures and flows can be adjusted for various working modes and that can be done in the monitor panel. Pump absorption torque can be adjusted to change the overall performance of the machine and the auxiliary circuit can also be adjusted to accommodate attachments. But I don't think that is the problem. There are safety suction valves for each circuit and a compensator for each function that can cause the low pressures. The boom an arm have regeneration and throttling valves as well. It doesn't help that the service manual doesn't do a good job of describing how all the functions are supposed to work if one were operating the machine. If the machine had a lot of hours I would guess a problem with the circuit reliefs/safety suction valves or the compensators.
I haven't had to work on these Dash models but have done many inspections and appraisals. I did receive a manual from a member and can study it for a bit for a clue or two.

lilbunk480, can you check those items I stated above to see if the operation is what I described? I think Komatsu what stay operating the same way through the years but change how it does that.

 

[lilbunk480]

I found out that my suction safety valves were adjusted low for a long reach front, got those adjusted and I'm off to the races!

 

[John C.]

Are those cartridges adjustable without taking them out and apart?

Do the rest of the functions still work the same as the older machines? Swing brake giving you power max, pump merge when traveling and working another function, and finally two stage relief when power max is energized.

 

[lilbunk480]

Yes I could adjust them without taking apart, the rest of the functions are working correctly!

 

[funwithfuel]

There is a switch on the right side for "raised" boom pressure. Its used for switching to a long boom and back. Do you have an ops manual?