My guess is that item 80 is the load check and not a relief valve.
I don’t see any work port reliefs in that parts break down
That hydraulic diagram shows two double acting cylinders, one extending while other is retracting so push and pull circuit.
OldnSlow, thanks for your insight, it always helps. I agree that item 80 is a typical load check that we find on most control valves - and that it is not involved in the swing problem we are working on.
Yes, the work port relief valves, aren't shown in that parts break down. For some reason the parts book shows the reliefs on the next page, and we see them again in the attachment to post #18 above.
A couple of things are interesting gleaned from the parts & shop manual:
1. identical relief valves are used for extending and retracting each cylinder. These are only used on the backhoe control valve. There are plenty of other different relief valves on other hydralic circuits on the M59.
2. There are two part numbers for the BH relief valves: Dipper and swing use one # (4 total).
The boom, bucket, and thumb use the other. Like
M59owner, I suspect that the difference is the relief setting.
The swing cylinders are double acting and also have their own dedicated swing pump which has yet another primary relief valve in the 3pt case. And interestingly it runs at a sligtly lower pressure than the main. But I don't think either is part of this swing problem.
Air bubble would not cause a relief to fail but a piece of contaminate certainly will especially if that is the style of relief that also has anti-cavitation check built in. The check opens at real low crack pressure to draw oil from tank line to help keep an over running cylinder full of oil. Then if check sticks open it prevents the relief from building pressure.
Right on! That style relief valve does indeed have an anti-cavitation feature. It works by comparing the working pressure vs the "return to tank" pressure....which means that the return to tank pressure is NOT ZERO. It is lower than the working pressure but still significant. Several hundred psi is my guess.
I'm stop here, but will say that anti-cavitation as it is designed in this valve means that sump tank fluid level is important...BUT way more important is to avoid any leaks in the BH hoses&connections - that is absolutely critical.
To a lesser degree of importance, I personally would not let the BH components move around much without the engine running. Use the swing and boom locks. Maybe add a chain on the bucket & dipper.
Any of these could cause temporary BH movement problems just because of air in the system.
My best guess is that debris does about the same thing as air in the relief valve, but not so temporary.
rScotty
