PC120-6 weak hydraulics

[fastline]

The display panel is ruined by ultraviolet rays that burn the panel out. It was a known problem that Komatsu supplied a filter plate for to prevent the issue way back in the nineties. Once burned there was no repair, only replacement.

I agree with that, thus why I have been covering my switch gear with a towel. It appears this is an LCD not LED display and those are more tricky to repair as I would need to verify actual display specs for replacement, and that certainly is not a DIY type project. Those would use a solder header on the PCB. Still worth the effort on something like this IMO.

 

[LACHAU]

Guys, Chinese magicians do retail this LCD monitor.
We bought one to replace the PC120-6 monitor. Its quality depends on your luck or not!

 

[blanchb]

Thanks Lachau. I’ll look into replacing the monitor display panel.

Since we are on the topic of “Chinese Magicians”. I attached a screenshot of part of the conversation I had with the place I bought the main relief valve from. I had asked them if the relief valve was already set and ready to install right out of the box. And if so what was the relief set pressure that it was calibrated too.
This is their reply.



Based on Lachau’s documentation. It says the low end should be set at 1.27 mpa (185psi) and the high end set at 2.94 mpa (426psi). They are saying theirs is set to 320psi? But they say it ready to install right out of the box? I asked her to double check with their engineer and she did. What do you think?
I’m kind of confused because I thought that the set pressure would be somewhere around 4500psi. Maybe I’m wrong on my conversion from mpa to psi? Or I’m not understanding how the settings work on the relief valve?

I attached a copy of the document that Lachau posted. And I also sent them the same document.

 

[LACHAU]

Thanks Lachau. I’ll look into replacing the monitor display panel.

Since we are on the topic of “Chinese Magicians”. I attached a screenshot of part of the conversation I had with the place I bought the main relief valve from. I had asked them if the relief valve was already set and ready to install right out of the box. And if so what was the relief set pressure that it was calibrated too.
This is their reply.

Based on Lachau’s documentation. It says the low end should be set at 1.27 mpa (185psi) and the high end set at 2.94 mpa (426psi). They are saying theirs is set to 320psi? But they say it ready to install right out of the box? I asked her to double check with their engineer and she did. What do you think?
I’m kind of confused because I thought that the set pressure would be somewhere around 4500psi. Maybe I’m wrong on my conversion from mpa to psi? Or I’m not understanding how the settings work on the relief valve?

I attached a copy of the document that Lachau posted. And I also sent them the same document.

OMG!!!
I remember very well that I posted the pressure settings for this machine already!!

The maximum pressure of the main relief valve has 2 values:
1/- In normal mode is 31.85 MPa (4619.45 psi).
2/- In power-max mode it is 34.79 MPa (5045.86 psi).

 

[John C.]

The 320PSI to 426PSI range is the pilot pressure relief cartridge and not the main relief.

 

[blanchb]

OMG!!!
I remember very well that I posted the pressure settings for this machine already!!

The maximum pressure of the main relief valve has 2 values:
1/- In normal mode is 31.85 MPa (4619.45 psi).
2/- In power-max mode it is 34.79 MPa (5045.86 psi).

View attachment 272609

Lachau.
I definitely didn’t mean to misquote you. I do remember that you posted the document with the different max pressures for each function. It was the same document just like the last document that you posted.


That’s why I’m confused about the main relief pressure settings? I must be reading this document wrong.

 

[blanchb]

The 320PSI to 426PSI range is the pilot pressure relief cartridge and not the main relief.

I worked all night last night and didn’t get home until 5:00am this morning, so I didn’t get much sleep. Maybe that’s why I’m so confused about this.

 

[LACHAU]

 

[LACHAU]

This is working principle of 02 stages main relief valve.

 

[LACHAU]

for more detail.

 

[blanchb]

Lachau.
Thank you soo much!! I’ve been straining my brain trying to figure out how this relief worked. Now, after reading this and comparing what I’m reading to the pictures numerous times I think I finally got it. there is a very small flow going through both relief orifices even during normal operation. It’s not until the flow increases more than the orifice design that a D/P is formed creating a low pressure on the down stream side of the main poppet thus causing the spring to compress and the poppet to move pass the oil passage holes to let HP oil go into the LP chamber. The higher pressure setting just increases the amount of pressure needed to create that D/P.

Thanks again for your knowledge, patience and understanding.

So what are your thoughts on what the suppliers engineer said about the set pressures on the relief valve that they are sending me? The 320psi?

 

[blanchb]

The main relief valve finally came in and I installed it. I cranked up the machine at low idle and it put out 4500psi. I was a little worried about over pressurizing the system and causing the relief valve to open so I backed down on the TVC adjustment. It really didn’t make a difference on the pressure. The pressure stayed at about 4500psi when loaded even the engine was at idle and even with the tvc adjusted down. I slowly increased the rpm’s to max and the pressure wouldn’t go above 4500. So I guess load sensing is working and de-stroking the pump. The movements were very slow so I increased the tvc adjustment and the movement speed got much faster. The tracks are much more powerful, actually better than they were before I had problems. I adjusted the tvc while working the machine and based the adjustments on the engine load/speed. I did make adjustments on the LS adjustment but it didn’t have that much of an effect.
So all that said, I do believe it’s fixed now. And the main relief valve was the culprit the whole time.
I’m at a part of my job that I don’t need the excavator much. So I still need to make time to run it all day to see if it continues to preform good. I will measure the hydraulic oil temperature and pressures after running it for a long time to see if it gets hot again and loses pressure. But so far I ran it over 2 hours and the temperature and pressure stayed perfect. So good that I blew a hydraulic hose.
I’m going to need to make a few more adjustments because the movements are fast and powerful but the levers response is a little delayed.
I’ll keep y’all informed.
I would really like to thank everyone on this forum that helped me. Without y’all’s help I wouldn’t have got it fixed. The knowledge and experience y’all have and information, direction and documentation that y’all provided is so valuable and appreciated by a guy like me you can’t even imagine how much I appreciate it.
So thank you again Lachau, John C and even Fastline.

 

[LACHAU]

Congratulations you have solved the problem with your machine.
Your joy is also our joy (the people who participated in answering this post).
To be honest, I was a bit apprehensive at first (since you said you're not a professional excavator repairman) so we weren't sure if our posts would help you.
But in the end, we realized that you have a very good background, so you have put our suggestions into practice very well.
Once again, congratulations on your success.

 

[LACHAU]

.....I did make adjustments on the LS adjustment but it didn’t have that much of an effect.
.....I’m going to need to make a few more adjustments because the movements are fast and powerful but the levers response is a little delayed.....

"Adjusted LS but it doesn't have much effect".
You don't feel this effect on speed and power but it has a different effect, bro.
The slow response of the levers is a consequence of the incorrect adjustment of the LS valve.