Hello, I'm looking for some direction in resolving what I believe is a spool valve problem. Pretty sure this is a Husco valve, what I have matches what is in the Parts/Owners manuals for the Clark Michigan 75A Series I . I've included the parts diagram from the manual for the valve. At some point in the loaders life an external filter was added on the return side going back to the tank. I've been using AW-46 hydraulic oil. Problem: The boom lever periodically moves back on its own, from neutral position to lift, and the boom begins moving up. It does this with more force at higher rpm's. When the boom lever is held in the neutral position by hand everything seems to work normally, however if the lever is not physically held in the neutral position it will usually pop back to the lift position and the boom begin to rise again. There is no external leaking anywhere in the system that I can tell. What I've Tried So Far: I drained the system and removed the spool valve assembly. Removed the detent cover, detent spring and caps, then slid the spool out of the valve body. There is enough wear in the detent cover that the wear can be felt when running a finger inside, but does not seem extreme to me. The spool looks good and slides snugly in the valve body without any binding or catching. I did not remove the check valve from inside the spool (...yet). When in operation the detent can be felt moving through the positions ( lift / neutral / down / float ), it does feel on the weak side though. Also, I've noticed there is a lot of oil in the detent cap/cover #1, not sure if it's supposed to be there? Pondering The Problem: In the diagram this valve is represented by the parts #1-16. I suspect that either the spool is not centering when in neutral or possibly a weak spring #7 in the check valve. I don't doubt that the detent spring #3 is on the weak side ( it's 60 years old... ) but not sure how this would account for the pressure on the spool -> boom lever that makes it want to pop into lift position, unless it's loose and there just happens to be enough play that it starts allowing fluid through...? The seal #5 is bad leaking...? Another thought, if it's alignment could the gasket #4 could be doubled up to set the detent further back, moving the spool away from the lift position and more into the neutral position...? (possibly just a band-aid over a bigger issue) I may be barking up the wrong tree here, any thoughts or direction on how to proceed at this point would be greatly appreciated!
Update: I'm in the process of draining/removing the control valve assembly again and can see on it that it's NOT a "Husco", it's a Hydreco V4DF70D . I've included an image of the inside of the Detent Cap to show the wear. Also, on the Detent Cap there is a rubber O-ring, however the parts manual refers to this as a 'gasket', could this be an issue as far as alignment?
I'm assuming that moving the spool to the right is lift, correct?
Correct. I also just noticed this damage on the spool that I missed the first time I looked at it. Is this enough to cause the behavior I've described?
and if so, I suggest that the spool is being pushed to the right by pressure in the detent cap. I would guess the green areas are tank return but are building enough pressure to overcome the detents. I would be checking for a restriction in the return to tank circuit. Without a schematic, it's difficult to comment further.
Yes, possibly. Following on from my earlier assumptions, if there is enough internal leakage in the valve to overcome the resistance in the tank drain circuit and raise the internal valve pressure. But if the same circuit takes the tank return from the cylinders as well, I would think it unlikely.
I'll work on putting an accurate schematic together to share. I'm going to head down and get a replacement oil filter right now. It's in the return side of the circuit and probably hadn't been changed in a decade ( I just got this machine a week ago... ). Your theory makes sense to me, there doesn't seem to be a direct path for oil to get into the Detent Cap though, but it's there, maybe from the restricted return path as you've suggested?
The cap has to be vented to tank somehow, whether through an internal passage or just clearance up the sides of the spool I can't say. But it has to be there.
Not sure if this is what you had in mind for a hydraulic system diagram, it's pretty simple. I re-assembled everything, put a new filter in (as I said before I don't see where the original system ever had a filter? ) and tested it. If anything there seemed to be more pressure then before against the spool moving it into the lift position, it will not stay in neutral position at all. It would seem, as you pointed out, this has to be the result of too much pressure on the return side in the valve, most likely in the detent cap. So that pressure must be either the result of a restricted return path ( again as you pointed out ), or the high pressure side is somehow leaking over into the return side very quickly? I'm going to add a pressure gauge to the return side to verify this. What sort of pressure range should I expect to get if this were a normally functioning system?
If the tank is open to atmosphere, the pressure in the return line should be virtually zero. Can you run a temporary line from the return port on the valve straight back into the top of the tank?
Ok, I mounted a 0-300 psi gauge on the return side of valve... Results: idle... ~5-10 high rpm... ~45 high rpm, boom lifting... ~25 high rpm, boom dropping... ~50 I'm wondering if the filter that had been added is restricting? I agree that is what I'll set up next! If the filter is restricting would it be better to put it between the tank and the pump?
Do you mean the actual whole filter assembly has been added into the circuit by someone and isn't OEM? No. Don't put a filter in the suction line. The only restriction here should be a screen in the tank at most, and that may already be there.
Yes, the filter system was added, NOT OEM. Here is a picture of it on the opposite side from the spool valve. I can't find any reference to a hydraulic filter and it's not shown in the diagram... I removed the filter and joined the two lines that were connected to the filter. I blew through the line connected to the tank and it was wide open. Also, there is the fill/vent on top of the tank so there shouldn't be any pressure building up in the tank. 2nd Test: idle... ~0 high rpm... ~25 high rpm, boom lifting... ~5 high rpm, boom dropping... ~40 It seems better... tomorrow I'm going to check the return line coming from the valve to make sure it hasn't started collapsing or something. Is it possible the relief valve is set too high or somehow effecting the pressure on the return side?
Cmark, you're a genius! The problem has been identified. The return line from the valve to the reservoir was creased/collapsing, the resulting pressure from this in the detent cap was forcing the spool out (into the lift position). As we discussed earlier I set up the return to go directly back into the top of the reservoir. This time when I tested it, even with the engine at high rpm and the boom and bucket in motion, I could barely get the pressure needle to move off the zero mark!
For What It's Worth... Before all this testing I had removed the valve assembly (AGAIN!) and this time went completely through it. One thing I did come across was what I felt was significant wear in on the relief valve and seat. At least if this were an engine valve I'd be concerned... I measured the adjustment setting with micrometer before disassembling to make for a quick and rough re-assembly. Tomorrow after I re-plumb the return line issue I'll hook a high pressure gauge up and set the relief valve correctly. Hopefully I'll be able to get the desired pressure even with the wear in the valve.
One last thing for tonight... (sorry for the multiple posts but I'm only allowed to insert 4 pictures per post...) Something that had me baffled was that there was no mention of any type of return from the valve to the reservoir in any either the parts or owners manuals that I could find, nor was it referenced in the diagrams. However, one diagram does mention a seal on top of the valve assembly but with no explanation. What I've concluded is that there is no return line, instead the return occurs through a hole in the top of the valve and one in the bottom of the reservoir with a seal clamped in between by the valve mounting bolts. This had me confused because at some point in this machines history these holes had plugs put in them with the tops filed off, I'm assuming to re-route the return through the filter that had been added. I'm a visual learner and like it when I can 'see' what someone is talking about. Maybe this will bring some clarity to the topic for someone down the road. I'll post more after I get this issue functioning properly, thanks so much for all the help and insight!!!
Yeah. I get that a lot. *wink*
Thought I'd add a final post to this thread, sort of a conclusion, I always like to know how things turn out anyway. I re-plumbed the hose route that has problematic with steel line, and also added the filter back in but mounted it right on the side of the reservoir with a custom pipe fitting I made up. So far everything seems to be working good with no return back pressure or creeping. I still need to set the relief valve to the exact pressure, but it is currently pretty close to where it was without issue. Now on to some of the other issues this old boy needs to get back into the game... think I'll start with the brakes, brakes might be nice