Need help with crane check valves leaking

[GarethVW]

I have a very frustrating problem with my crane. It is a '84 national 500 series and the problem is the check valves in the outriggers don't always lock. So, I go to set up and the outriggers will not hold, they leak down. But, what is frustrating is that it never happens when it is warm and only sometimes happens when it is cold. I checked the cylinder by setting the outrigger and capping the line and it will hold. If I remove the cap fluid will leak out and the outrigger will slowly collapse. Now for the frustrating part, I changed the check valve in one of the outriggers and it didn't make any difference, it will still leak sometimes and not others. And the other one that I didn't change is doing the same thing. And now the main boom cylinder is leaking down as well. I am stumped, I though about changing the fluid but I don't know if that will help. Has any one had anything like this happen?

 

[CalTreeEquip]

There must be a master pressure relief valve that has weakened. You'll want to adjust that I would thing.

 

[GarethVW]

There must be a master pressure relief valve that has weakened. You'll want to adjust that I would thing.

Is this what would set the operating pressure of the system? How would this cause my problem? Thanks for your help!

 

[CalTreeEquip]

I was thinking "control valve" but then all your rams started to bleed down. I think (not sure about this at all) that if there is a master relief valve it might allow for all the circuits to bleed pressure. Just a simple minded guess though. I don't know that whole system.

 

[VA-Sawyer]

When you say it only acts up when it is cold, how cold are you talking, below freezing?

You might have suspended moisture in your fluid that is forming ice crystals at cold temps. The ice can cause problems for the check valves. It would explain why the new valve didn't change anything. It also sounds like it is spreading to other parts of your system.

If not moisture, it could be some other contamination such as; sand, metal shavings from a failing pump, unwanted chemicals, even saw dust. Perhaps the filter is clogged and is in bypass mode allowing the problem to spread.

I would suggest looking at the fluid, and changing it, if it looks anything other than new. Filter too.
You could also have a lab do an analysis of a fluid sample. Check online for a lab near you. Should be able to have it checked for under $75. Just be sure to follow the instructions when collecting the sample.

Rick

 

[dbl612]

check valves

from what you have described, that the problem has continued after changing check valve cartridge, it would seem that the cylinders are leaking internally. easily checked by putting unit up on o/r, disconnect lines from valve bank to lock valve, if oil continually leaks from from rod side port on cylinder the packing is leaking internally. this situation would be more pronounced when oil and cylinder are cold because the packing is contracted. has nothing to do with pressure settings, national uses an open center hyd. system-lines open to tank when control valves are not actuated. (thats why lock valves work- they require pressure to release and let down the boom, raise the outrigger jacks, or release the brake on the winch.