Hydraulic Pressure Issues

[Marc51]

I have a 2015 Komatsu PC55MR-2. Its an offshore machine.

There are 3 things that aren't right with the machine. I am not sure if they are directly connected issues so I will lay them out seperately.

Issue #1 - The control valve for the dozer blade is malfunctioning. ( I have ordered a used replacement.) Currently the pressure is bypassing the valve and it allows leak down when the blade is up (and no down pressure). Essentially it is circulating fluid = wasted power.
Issue #2 - The hydraulics all work normally but at a slightly lower speed, I blame issue #1 for that.
Issue #3 - When the hydraulic cylinders on the machine reach their maximum or minimum stroke (in or out) the machine continues to try and push fluid. If I hold the control a little to long I can hear the hydraulic pump draw down the engine and if held too long it will stall out the engine completely.

Should the extra hydraulic pressure even be there? Once maximum or minimum cylinder stroke is achieved, should it just bypass that extra pressure and return to the tank?

Not sure where to start looking. Do I have too much pressure? Why am I able to keep pushing pressure into a cylinder and stall the machine?

 

[Coaldust]

I would first focus on issue #3. The pump isn’t de-stroking for some reason and going back to neutral, for lack of a better term. Can you post a picture of the pump so we can see what you are dealing with?

Before going much further, I would remove the hydraulic filters, cut them open, and see if you are dealing with a contamination issue or a trashed pump.

 

[funwithfuel]

The 55 is a weak little hoe in the first place. I believe, iirc, it has a naturally aspirated 3 cylinder Yanmar engine. The pull down is probably a control valve issue. I would put gauges on it so you know what's what. Then we can look deeper into what is doing what.
Have you checked the dozer blade cylinder bypass? The dozer blade is usually isolated from pump 1 and 2, running off a small fixed displacement pump of its own.

 

[Marc51]

Thank you fella for your responses.
I left out a lot of other maintenance I've done....
I had the blade cylinder tested, its fine, the only other thing is the cab control which is a steel valve in an aluminum body. Replacement is $292... should make the blade usable and give back hydraulic power to the rest of the machine (in my head anyway). While having the cylinder off, I drained the hydraulic tank and replaced the filter element.
Today... I wanted to see if it would even lift itself and it does. I put it through its paces and issue #3 has gone away mostly... its getting better it seems. The overall speed of the machine still seems slower than it should be, I could be wrong on that too.
For now... I'm waiting for that valve and hope that also improves performance.
The hardest part of an offshore machine is cross referencing it seems... all the parts are here (Canada), just have to find the numbers. For the most part I use a PC50MR-3 as the closest relative.

 

[Marc51]

The 55 is a weak little hoe in the first place. I believe, iirc, it has a naturally aspirated 3 cylinder Yanmar engine. The pull down is probably a control valve issue. I would put gauges on it so you know what's what. Then we can look deeper into what is doing what.
Have you checked the dozer blade cylinder bypass? The dozer blade is usually isolated from pump 1 and 2, running off a small fixed displacement pump of its own.

Its a 4 cylinder Yanmar 4D8EE model I believe.

 

[funwithfuel]

If someone was in there messing around, they might have bottomed out the main relief. Yes, ideally, when you reach end of travel but still hold function the relief should open at a predetermined pressure to allow the eccess to return to tank. That's why pressure values are so important. If the engine is stalling before reaching the unload pressure, we gotta look at fuel n air. If the pressures are exceeding values, we gotta find out why. Is the pump not destroking, is the relief pressure too high, is there an obstruction? This is all basic troubleshooting, we can help you through it, but it will require gauges, basic hand tools and patience.

 

[Coaldust]

Well said, Mr Funwithfuel.
I’ll add one more requirement. Money. Lots of money to toss at that Grey-market machine.

 

[funwithfuel]

Fo sho!