Pilot pressure too high

[Sachin]

Friends,
I have inspected a pc300 komatsu excavator , due to machine slow.
I have noticed the pilot pressure at nuetral condition is around 45-50 bar which was supposed to be 32-35 bar. And also noticed the pressure increasing beyond 100 bar when each attachment is operated. I have checked sprv but found no problem and confirmed it with replacing by another sprv. What will be the cause?

 

[John C.]

What is the Dash model? How many hours show on the meter? Have you tried adjusting the pilot pressure? Are all the functions affected? Does the machine travel in a straight line?

 

[Sachin]

What is the Dash model? How many hours show on the meter? Have you tried adjusting the pilot pressure? Are all the functions affected? Does the machine travel in a straight line?

I have tried adjusting pilot pressure but not increasing neither decreasing. All functions are affected. I have connected the gauge for checking pilot pressure and gauge is showing above 100 bar each time i move an attachment. Suspected problem with sprv and changed the same, but still same issue.

 

[Sachin]

What is the Dash model? How many hours show on the meter? Have you tried adjusting the pilot pressure? Are all the functions affected? Does the machine travel in a straight line?

Pc300lc-7 model
11000 hours

 

[John C.]

It kind of sounds like you are getting load sense or main pressure into the pilot system. As I recall, sometime around that series of machine, Komatsu started using a pressure reducing diverter valve mounted to the inlet side of the main control valve for pilot pressure. I would suspect a problem in that valve.

 

[Sachin]

Th

It kind of sounds like you are getting load sense or main pressure into the pilot system. As I recall, sometime around that series of machine, Komatsu started using a pressure reducing diverter valve mounted to the inlet side of the main control valve for pilot pressure. I would suspect a problem in that valve.

There is only a self pressure reducing valve attached along with merge divider. I have swapped it with that of a working machine but problem still exists. Is there any chance of pilot pressure build up if merge divider solenoid is stuck?

 

[John C.]

I haven't had to work on those so I can't tell you. By any chance, does the travel speed work properly or might it be stuck in high all the time?

 

[Sachin]

I did not put enough pressure on the actuators and motors, as the pilot pressure is increasing. There is a chance for bursting merge divider spool cups. So i could only do anything only after solving this issue.

 

[John C.]

I think I would be looking for any point where oil could bleed out of a function and into the pilot system. On older machines, the travel speed circuit was usually the bleed point but I suppose it could come back through the swing brake circuit. The other symptom we used to see with main oil getting into the pilot system was the joy stick controls would get tight and hard to move.
My other thought is that high pilot pressure would not cause the machine to run slow. Do you have a service manual for the machine?

 

[Hydraumind]

Pilot pressure cannot reach 100 bar because the sprv has a safety valve opening at 45 to 50 bar in case the sprv relief stuck closed. Use another presure gauge and test again

 

[Sachin]

Pilot pressure cannot reach 100 bar because the sprv has a safety valve opening at 45 to 50 bar in case the sprv relief stuck closed. Use another presure gauge and test again

Have tested with another gauge and noticed the same.. Is there any other chance if there is any block in tank return lines. Or is there any chance of main pressure getting in pilot pressure checking area

 

[Hydraumind]

The sprv has a return line TS, try to disconnect this line and check if it leaks while testing. Did you remove the divider valve? Make sure the sequence valve didnt fall, in this case high pressure can get into prv pressure

 

[Sachin]

As you said, Tank line was blocked. Now pilot pressure problem solved.

Now new problem is main pressure we are getting only 224 bar where 350 is required. Have replaced mprv both , but no change in main pressure. Every attachment relief pressure is 224 bar only. Can you help what will be the cause

 

[Hydraumind]

Hydraulic pump

 

[Sachin]

Pump is not giving enough flow?