PC55 unload pressure too high

[Amjad.kamal]

Looking for some help for my pc55. Just changed the pump and control valve due due to some issues. Things seemed to be fine until I put a pressure gauge on the P1 output and the unload pressure is reading around 900 psi which about 450 psi higher than it should be. What should I be looking at as source of the issue?

Work equipment works fine and strong.

 

[Kobe Steel]

Looking for some help for my pc55. Just changed the pump and control valve due due to some issues. Things seemed to be fine until I put a pressure gauge on the P1 output and the unload pressure is reading around 900 psi which about 450 psi higher than it should be. What should I be looking at as source of the issue?

Work equipment works fine and strong.

Check that your load sense pressure from your control valve to the pump is correct and is not reading well above tank pressure when in neutral operation ( lever lock disengaged). Check that the pump minimum flow stop setting is correct and not set too high.

Best regards

 

[Amjad.kamal]

Thanks Kobe. The LS pressure is right at spec around 450 psi. I am not sure how to adjust the minimum pressure. I tried adjusting PC valve on the pump and it didn't make any difference.

 

[Kobe Steel]

Thanks Kobe. The LS pressure is right at spec around 450 psi. I am not sure how to adjust the minimum pressure. I tried adjusting PC valve on the pump and it didn't make any difference.

Hi Amjad

When I was referring to the LS signal pressure I was referring to the Load sense line itself and not the load sense differential pressure. When all functions are in neutral, the pump pressure port p1 and p2 should read your unload pressure of 450 psi and the pumps load sense port theoretically should read near zero or close to tank pressure. This is your load sense differential reading otherwise stated as Main pump delivery pressure - load sense pressure = LS differential pressure.

The PC adjustment is for pump torque control and should not need any adjustment unless you are doing a performance test on the pump. I may be able to point out pump adjustments but I would need to know the full model code of your machine and seral number.

Try taking the LS line off the pump and plugging the hose connection and leave the LS port on the pump open to atmosphere. Read the pump p1 and p2 pressures and see if they go to 450 psi.

If both pump delivery pressures go to 450 psi then you may have a load sense signal being applied to the pump or the load sense line is not draining back to tank via the control valve

If both pump delivery pressures stay at 900 psi then you may have an issue with
both unloader valves or
a flow restriction or
the pump minimum flow is set too high

If only one pump delivery port pressure goes to 900 psi, then there may be an issue with that pumps unloader valve or a flow restriction

Best regards

 

[Amjad.kamal]

Thanks for clarifying that Kobe. I've put a pressure gauge directly on the LS line (between control valve & the pump with a T on the pump side) and am reading a 450 psi pressure at idle rpm with no load. I will try taking the LS line off the pump (I need to find a plug for that line) to see if the unload pump pressure drops.

What could be causing the LS line pressure to be around 450 psi in neutral (at idle rpm) when it should be near zero?

 

[Kobe Steel]

Thanks for clarifying that Kobe. I've put a pressure gauge directly on the LS line (between control valve & the pump with a T on the pump side) and am reading a 450 psi pressure at idle rpm with no load. I will try taking the LS line off the pump (I need to find a plug for that line) to see if the unload pump pressure drops.

What could be causing the LS line pressure to be around 450 psi in neutral (at idle rpm) when it should be near zero?

Some possibilities I can think of are..
a function that may not be returning to neutral.
Main pump pressure is bypassing into the LS circuit in one of the control valve sections.
Confluence valve in the valve bank is shifted or stuck in the wrong position.

Best regards

 

[Amjad.kamal]

Hello Kobe, so the pressure drop right to 450 psi on both p1 and p2 when I took LS line off the pump. So it's definitely false load signal. I took the TS line (return line to the tank at the end of the control valve on the work equipment side) and there is no oil draining from that port when there is no load. If I put load there is oil coming out in a steady stream. I took the spool out on the logic valve where the LS port is and took the shim out from the spring and the pressure dropped by about 20 psi. Could this be a spring issue on that spool?

 

[Kobe Steel]

Hello Kobe, so the pressure drop right to 450 psi on both p1 and p2 when I took LS line off the pump. So it's definitely false load signal. I took the TS line (return line to the tank at the end of the control valve on the work equipment side) and there is no oil draining from that port when there is no load. If I put load there is oil coming out in a steady stream. I took the spool out on the logic valve where the LS port is and took the shim out from the spring and the pressure dropped by about 20 psi. Could this be a spring issue on that spool?

Interesting find. If you were to remove and plug the LS hose on the pump and put a test point in the LS port of the pump would you see the test point pressure increase at all and if so how much over what time span?, just a thought.

 

[Amjad.kamal]

I didn't check that but I am not sure what that test be indicative off?

As an update, I have put a T on the pump LS hose and joined it to the return line on the TS port by putting another T there and a flow control valve just before the T to be able to control how much LS pressure I am leaking. If I keep the flow control valve close the pump gets the full load signal (which is a false signal and I can't figure out why that is) and so if I crack the valve a little bit it's drains and drops the unload pressure.

However, I've run into a different issue. While I was testing the hydraulic function, the right track came off the idler. Despite my best efforts, I can't get it back on. Took the idler out and the tensioner rod is sticking out about 2 inches after releasing the grease pressure. I've pushed it using my tractor and it won't budge. Can't quite figure out of the rod is supposed to be flushed with the bore when fully retracted or the 2 inch sticking out is normal? Do you have any experience with the track tensioners on komatsu minis?

 

[Kobe Steel]

I didn't check that but I am not sure what that test be indicative off?

As an update, I have put a T on the pump LS hose and joined it to the return line on the TS port by putting another T there and a flow control valve just before the T to be able to control how much LS pressure I am leaking. If I keep the flow control valve close the pump gets the full load signal (which is a false signal and I can't figure out why that is) and so if I crack the valve a little bit it's drains and drops the unload pressure.

However, I've run into a different issue. While I was testing the hydraulic function, the right track came off the idler. Despite my best efforts, I can't get it back on. Took the idler out and the tensioner rod is sticking out about 2 inches after releasing the grease pressure. I've pushed it using my tractor and it won't budge. Can't quite figure out of the rod is supposed to be flushed with the bore when fully retracted or the 2 inch sticking out is normal? Do you have any experience with the track tensioners on komatsu minis?

a lot of the idler pistons I have done usually do have a certain amount of the piston protruding from the piston housing. I would often use a block of wood and the digger bucket to gently push the idler wheel all the way back with the grease fitting fully removed. The idler spring assembly also has a stopper at the top of the spring that recesses into the frame as well.

The test for the ls I mentioned before is to see if the false load sense signal is coming from the control valve or if its coming from the ls port on the pump itself.

best regards

 

[Amjad.kamal]

Thanks Kobe, I was able to get the track back on.

So if, I understand correctly, you are suggesting to put a pressure gauge directly on the Pump LS port and plug the LS line coming from the controller (and do vice versa)?

 

[Kobe Steel]

Thanks Kobe, I was able to get the track back on.

So if, I understand correctly, you are suggesting to put a pressure gauge directly on the Pump LS port and plug the LS line coming from the controller (and do vice versa)?

Good work on the track, they can be a pain sometimes that's for sure.

Yes, I'm wondering if the LS port on the pump could possibly be bleeding a lot of oil out of its own port verses LS pressure possibly coming down the LS line from the control valve. Just a random "what if" thought I had when I was looking at a circuit diagram and going over your test results so far.

Best regards