The machine has never been able to push/lift its self up off of the tracks for years. Today I had the time to check the pressure and test the cylinder. The cylinder tested with no issues at 3500 psi. I then checked to see if I needed to turn the pressure up. The pressure would not reach more than 500psi pushing down but booming up to the max went to 3500psi. For some reason the boom down pressure will not go above 500psi checking it at the valve. Any thoughts? Could there be a pressure bypass opening not allowing it to have down pressure?
has anyone had this issue with the volvo mini excavators?
Have you tried swapping the boom cylinder port reliefs?
Yes sir and no change, still 500psi down and 3500psi on the up boom. Is there a pressure relief somewhere else besides on the bottom and top valve, maybe somewhere under the floor above the turntable? Any other thoughts?
Where are you measuring your pressure? The only thing in the circuit from the spool to the boom rod end port is the port relief. Does this happen with the pattern change valve switched? Is the pattern change valve all the way in one position or the other?
Thanks Ben, yes, I checked the pressure at the top and bottom of the spool with in-line gauges. I have not tried switching the control but this has been going on for sometime and I have switched from one method to the other (backhoe / track hoe modes). Is there any reliefs others than the ones adjacent the main boom spools for the main boom?
Not that would affect only the boom down circuit. The only reliefs are the circuit reliefs and the LS limiting valve, which affect all functions. When you say you "checked the pressure at the top and bottom of the spool with in-line gauges", do you mean at the hoses to the boom cylinder or the servo caps that actuate the spool. There is a pressure tap on the right side of the valve looking from the counterweight, pointing straight down. This should be your LS pressure which will tell you your working pressure.
Thanks Ben, yes, I checked the pressure at the servo caps for the main boom section. Any other thoughts?
And you got 3500 PSI at the servo cap for boom up?
yes sir, my plan is to switch the lines from another source, say run a lines up from the blade to the main boom and switch them to determine if that tells me anything.
Is your stand by and/or LS margin is 500 psi? You might have LS shuttle problem inside the DCV.
You don’t have to switch anything, just disconnect the line from boom down, plug the hose, install the tee for the gauge in to the work port for boom down, cap/plug the free end. Then activate the boom down function and watch the pressure. If the pressure will go to spec - then the problem is downstream from the DCV. If not - start checking LS pressure while activating the function, and/or port relieve.
Another thing - dead head some other cylinder while you reading the boom down pressure, if the boom down pressure will go higher than it does when you use only boom down - the problem is LS.
Are you checking pressure at the yellow arrow or the red arrow?
You should added goggly eyes imoji at the end of that phrase.
You are not exactly right - there’s a port relief on both work ports. That can be a culprit.
Standby pressure should be appr 310-335psi and there are no LS shuttles or check valves. That function is accomplished by the compensators in each spool section. I had already asked him if he had swapped the port reliefs. If you look at his question before that post he asked if there were any reliefs other than the port reliefs.
Is that post compensated DCV? Sorry I’ve missed the swapping port relief part.
Not 100% certain of your terminology.
The only LS DCV that doesn’t have the LS shuttle I know - is what they call “post compensated” DCV. Like CAT 420 backhoe have. Even Danfoss PVG100, which is Post Compensated DCV still has LS shuttle valves. Without the shuttle valves in pre compensated DCV you will not be getting the correct LS signal.
This is a LUDV LS system. This is not a "CAT" system or made by Danfoss. It should be Bosch as far I know. I would have to see what Cat is using on their TLB's now. The last one I worked on was 20yrs ag when I worked for the regional Cat dealer. Back then they called them resolvers.
I looked it up, Rexroth LUDV IS a post compensated set up. Although in the same stack can be just regular LS section, with pre compensated in-flow regulator. Rexroth is not too widely used in mobile equipment. Not like HUSCO or Danfoss. I remember older Cat dozers used obsolete now Rexroth MP series DCVs. The M4 series still in use in some mining equipment. I’ve learned something today.
Good evening and thanks for the assistance. So i switched the boom cylinder lines so that up was down and vice versa. With the hoses switched on the cylinder boom the boom down now lifts the machine and with the boom up, the machine does not have enough power to lift the boom. The boom also falls quickly and does not have enough power to lift anything? Bad spool? Thank you in advance for the assistance.
Don’t know about Ben - but now I’m not sure what pressure and at what port was measured, and what those values are. You can have low pilot pressure to shift the spool all the way. We would have to clarify. Look at the picture Ben sent, and answer the question.
Thanks, I have not check the yellow arrow hose (pilot) but tested the boom down (bottom of valve was 500 psi) and 3500psi on the red arrow or boom up.
I would test pilot pressures. Spool not shifting fully can cause that problem.
no, it was a smaller size inline connection and couldn't test it....
Well - you’ve got to “check out” all the possibilities, and be methodical about it. Even if one of the pilot pressures shows up too low - still the question will arise whether it is problem in the “joystick” valve, or leak in the spool’s “pilot land”.
I am still hedging that the port relief is causing your issue. To rule out the servo side of things swap the pattern change and see if the issue moves to the arm or stays with the boom.
Thanks Ben, I switched the pattern and still the boom down has now pressure. is there any thing else i could check, i assume that we can't switch the pilot lines to check if the problem still exists on the down pressure.
Does the boom drop quickly when you lower it? Is this the port relief you swapped top to bottom? The arrow just shows the very top of it behind that hose.
Thanks Ben, yes, the red arrow is the port relief that we changed to the bottom and no difference. I even tried turning the pressure up on the relief and no change either. I think that the booms drops about the same speed.
If you push the joystick forward all the way does it drop quickly or does it slowly lower?
Thanks Ben, I tried it again and it does not lower any faster than it raises.
Does the cylinder have any blocks on it?
I would definitely check that pilot pressure.
That is not what I was asking. Does it lower quickly? Boom down cycle time is 1.8 sec. This will tell you if you spool is moving enough. If measuring servo pressure to the boom spool the best place to do so is at the out let of the pattern change valve. Those valves have been known to leak internally in the past although not common.
Good evening, I was able to get my gauge on both sides of the boom spool and both tested at 450psi. I also pulled the caps and spool to see if I had a broke spring or something and then checked the lines from the spool to the cylinder and all good. spring inside one side of the spool appeared to be fine and I could not get the other side broke lose. Could the valve/spool housing have something wrong?
It would make it a lot easier for anyone reading the forum if abbreviations were at least explained when first used. Not everybody is familiar with everybody's else's abbreviations. Some are common and some aren't.
It would help if you wipe it off from the oil. Oil creates lots reflections as light distortions What is this? Is that the reflection. If something, or a deep gouge?