We have had Poclain excavators for decades, all that remains is a Case/Poclain 888. It's been here since 1998, in 2007 it was retired to farm duty (currently 66xx hours). It started to get slower, then it wouldn't hold it's boom up. Changed out the anti-drift valve, no change. About 100 hours later it stopped that and started to have NO power in the boom, had to dead end the stick cylinder in, or move the drive motors and it would jump to life. It's worked out OK for farm duty, clearing fence rows, etc. First job of the year (at a friends farm of course) and it looses power in the bucket, stick and boom, and the boom is "locked" in the up position. Started to do the test the service book calls for, right off the bat, pilot pressure is 400lbs vs the required 479-522lbs. I assumed this wouldn't let the anti-drift valve open, as it is tee'd off the pilot controlling the boom spool. My brother wanted to continue with the test, found the load sensor to be about 40lbs too light, but the hi-side hydraulics tested at the main spools at 1800lbs, should have been 3944lbs. Our service book doesn't show the type of pump/manifold we have, book says 888C, and ours it just an 888, s/n 74307. Borrow a book, no better, still not right. We just guessed and adjusted a regulator, and the old girl jumped to life! Picked it's boom up without issue, pulled in the stick with a full bucket of dirt, rolling it out of the bucket, it hasn't done that in 12-15 years. Boom still won't go down!! The pressure in the bucket/boom/bucket spools is now just a hair under 4000lbs (where it belongs). Disassembled the anti-drift valve, no apparent problems. There is no picture of this in any of the service manuals, and it's also not in our parts book. I was able to locate a used one, and will order it tomorrow. The only thing we can determine is it's the "relief valve" that is causing the problem. It appears to take the pump pressure down to pilot pressure, or at least break the seal it has to keep the boom up. Can we just take the guts out of this valve and it will use only the spool to hold the boom up? Will it mix high pressure with pilot pressure? I'm really hoping the replacement valve will cure it and back to work it will go. If anyone out there has the "old" service book, I'd LOVE to see it or get a copy of it. I think our machine was built in 1988. All our books are 1990-1991. There is no place on the net to discuss these old machines, hoping others will chime in with their solutions or problems. This is the valve I have.
I know nothing about these machines but my guess from the looks of this valve is that the pilot pressure shifts a spool against a spring under that cap with all the allen head bolts in it? Make sure all that looks good and if there are any seals on the spool that they look to be in good shape. If I'm correct in my assumptions you may not have enough pilot pressure to shift the spool. I'm also guessing the relief valve is just that, a relief to let oil flow in a situation where the boom is overloaded, rather than whatever component is weakest exploding from overpressure?
I agree... but for it to suddenly stop working makes me think it's something else. We turned up the pressure, I would think that also turns up the pilot controls. I ordered a used valve, the entire block in the picture, it will be here tomorrow... so we'll see what happens!!
Again, I know nothing about the CASE machines, but in my experience the pilot system is independent and has it's own pressure regulator. Anyway, you will soon find out more about it!
load holding valve Lowering the boom' If the hand control is moved to retract the cylinder, oil flows from the valve spool directly into the rod end of the cylinder. Oil returning from the base end must pass through the load holding valve. The check poppet is closed to oil flowing in this direction. System pressure is not high enough to open the relief valve. The only path open is through the pilot operated check spool. The pilot line from the hand control that moves the valve spool to retract the cylinder, is also connected to the pilot operated check spool. The same pressure is used to open the check spool to allow the oil returning from the cylinder to get back to tank. Did you check your M4 for pilot pressure, and do you have the Linde or Rexroth pump. Is you s/n above CGG0015401?
Sheepfoot!! You seem to have knowledge of this machine!! Wengers didn't deliver, sent the wrong part, and they didn't have the correct part. Typical Monday morning... called around had a few breakers looking for it. My brother and I took the valve apart and studied it for about an hour, we understood that the pilot pressure somehow opened a check valve/safety valve. When we checked M4, we got just over 400lbs... too low. This is where I thought the problem was all along, father and brother disagreed. The pressure regulator was turned up and the machine was working well, this was Thursday or Friday. Still the boom will not go down, rockets up, etc. Pressure at M1 is on the button now. We never did check M4 again. Act of desperation as I wasn't finding the valve block for replacement... we removed the poppet and spring, knowing the rest of the internals had to stay in place to keep high pressure from getting to the pilot system. What a treat to put it back together... It's been 10.5 hours and works like a new one! Throws trees with ease, holds trees in the air with the stick extended, and will hoist them higher. Amazing, hasn't done that since 2000-2001. My concern is, is the pump on it's way out? I'm assuming that's why we had to turn up the regulator. This worked well on the old Poclains, but this is a different animal. My father wants to turn it back DOWN a little, for fear we are stressing the system. I did blow a hose today, but it was torn for some time, I'm sure the higher pressure will kill some of the holder hoses. Sounds like you've had some experience with these machines. Do you have the correct service manual for this one? Parts book? We have a parts book that is very close, but does not show this load holding valve. AND... I'll NEVER trust the boom, I never did get under it, what so ever, but now, I won't get near it off the ground. If it were still on jobs lifting manhole bases, it would have to be properly fixed. Our S/n is 74307, I believe it's a 1988? Thanks much!
On the early machine's they did not come as standard equipment, safety valve/load holding was a optional for the boom and stick. We also had hose issues with them blowing, they were a good digging machine like said. The 400 psi is low, you are correct, it needs to be a min of 480 - 520 psi. You can take a look at the casece parts site and type in 888 for the different s/n parts pages that may help you some. I will look this week to see if I can find some old tech info, your year is about right for some of the first 888 with the linde pump, some changes were made to the 888 when they went to the Rexroth pumps and made load holding valves standard equipment.
Hello everyone, I have solved some things about the 1088 excavator, but I am stuck in a problem of the boom, is the only one that does not want to lift. I'm sure the pressure comes to the cylinder but something locks it up as if it were the return of the rod that is restricting it from rising. Any suggestions? Thank you. certainly the boom does not raise but if it comes back.
Hey, I have a 788 that im battleing, maybe you could come up with some advice, here is the thread