Hydraulic Valve rebuilding

[Paul007]

Considering the amount of ancient hydraulic stuff I have (loader, backhoe, dozer, dump truck and now stump grinder) it's amazing I haven't yet had to mess with the hydraulics save for blown hoses. Anyway I have an old Vermeer stump grinder that looks like it went through WWII but it's still going. One of the rams is creeping outward, unfortunately pushing the blade into the stump. The ram will move both ways but I need to eliminate this creeping. I know nothing about these valves. Yesterday I pull the lever off and tried to slide the piston (?) out but it wouldn't come, felt like maybe vacuum holding it in and I was too tired to pull a hose off.

What causes this creeping, is it something I can likely fix without too much cost or bother?

Here's a photo. I bought a mini-bike at the swap meet and had to lash it to the side to get home.

Paul in Calif.

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[Andy Martin]

Hydraulic valves have extremely close tolerances. Anything you do to them will destroy the tolerance short of building your own new spool. New valves are cheaper.

 

[Paul007]

Thanks for the reply. Yes I see new ones for under $100. Not knowing the insides I was thinking maybe new O-rings or a spring or something like a brake master cylinder would have.

 

[Den N Ms]

Paul007,I could also be a leaking piston ram seal in that creeping cylinder.Is the control valve a single or two or more.If the control valve is multiple type,disconnect another cylinder and swap with the one that is creeping to see if it is the valve or the cylinder that is bad.

 

[RM-MN]

Here's a video of repairing a hydraulic valve. You might want to take it to a hydraulic shop since they will have done this many times and will not put it together wrong but it really is something you could do yourself.
Untitled URL Link

 

[Paul007]

Thanks guys. Did some reading last night, most say a piston seal can't cause creeping because the unequal amounts of fluid on one side compared to the other due to the space occupied by the shaft prevents this (provided nothing is traveling through the hoses). Maybe so. Mine will creep all the way from closed to open if I don't move the valve, against gravity so it would seem some pressure it working against it.

Learned something from that video. I was trying to pull the shaft (spool?) out the wrong end, I would need to take the cap off the back side and slide it out that way.

At this point I am 75% done with the stumps I'm grinding so I think I'm going to live with it for this project rather than take the chance of having it down, then work on it over the winter.

 

[gbs]

if it's that old the cylinder piston seal is most likely leaking or a bad holding valve if it was equipped with one, contrary to some theories about fluid volume equalizing with in a hyd cylinder it ain't going to happen not on a dual action cylinder,most valves spools are close tolerance fit to the valve barrel and the only service is the end seals

 

[Paul007]

Got out to use the stump grinder yesterday and paid a little more attention to the drifting problem. Turns out the problem is the spool not automatically centralizing after moving it one way or the other against the springs. There is about half an inch of travel before it hits spring tension in either direction and if I carefully find the theoretical center the ram does not drift. I do not feel any detent, are the springs alone supposed to centralize the spool? If so it may be just a matter of week springs though getting new ones or stretching the old ones might be tricky to get it just right.

 

[Don-Wi]

I've got a valve I tore apart a while back because dad replaced it and it did what yours is doing. Turns out it has a broken spring.

Donovan from Wisconsin

 

[Paul007]

(quoted from post at 11:11:18 11/04/15) I've got a valve I tore apart a while back because dad replaced it and it did what yours is doing. Turns out it has a broken spring.

Donovan from Wisconsin

Thanks Donovan, yes that sounds quite likely. My stump job is done for now so I will pull it apart in a few days and report back.

 

[Jiles]

Years ago, I was a certified automatic transmission mechanic.
Had a lot of schooling back in the day.
I still hold to that training.
AT had many valves, springs, balls. There were some valves in a valve.
We were instructed to never use anything more course then a brown paper bag to clean a valve!
Reason being that they are that precision and mainly because they are "self cleaning" with the sharp edges on the valves sweeping any trash out. If you cut this edge, trash can enter between valve and valve body and cause binding problems.
As a last resort, very fine sandpaper can be used but STAY AWAY FROM the sharp edges!
Hope this is helpful.