OT-Update-Need a Hydraulics Expert

Formerly PaMike · Dec 2, 2010

So for those of you that saw my post last night, here is an update. The boom started drifting so I ran the boom up. I pulled the ROD side lines to see what would happen. Boom doesnt sink, and normal pressure (about 1200 psi) is maintained on the Base end. This shows the cylinders are OK. NOW THE WIERD PART. When I go to raise the boom up with the rod lines off, fluid sprays out of the rod lines. Nice big streams from the lines on both sides. Streams start and stop with the pedal movement.Somehow the pressure is getting out the wrong port. Instead of going to the cylinder port certain times it is going out the rod port. Ideas? Maybe a cracked valve block? I gotta go study the book somemore.

CAROGATOR · Dec 2, 2010

Maybe you crossed the lines when you built the valves?

Heat Houser · Dec 2, 2010

If you have oil coming out of the cylinder's rod port when it is all the way up (bottomed out mechanically) you have a piston seal leaking at high pressure. (unless it has a phaseing check valve in the piston)

Oil coming out of the line that would be connected to the cylinder's rod port....I suspect that the valve has anti cavitation checks. Once return gallery pressure goes up above the value of the check's spring, (and it will due to flow) the anti cav check opens since the line is open to atmosphere.

If you have a cracked valve, they tend to get worse as the unit warms up. Once warm, you can about pick the pressure you want to see by varying the engine RPMs. For this test, plug the lines going to the cylinders. Note, cycle times should be slower the bigger the internal leak.

Formerly PaMike · Dec 2, 2010

Can you dumb it down a little for me? Not following what you are saying with the anitcavition valves. My valve has "lift check valves" is that what you are referring to?

RodinNS · Dec 2, 2010

I can't tell you why youre getting oil out the return hoses... other than to say something is wrong in the valve. I also just remembered... those valve stacks are regenerative in that they direct return oil from the lift circuit into the work ports of the bucket circuit to increase the rollback speed.... or mabey it's the opposite. I forget exactly now... but it just complicates the valves a bit.
Best suggestion I can make is that you do a very carefull disassembly of the valve bank and see what you find.

Rod

Formerly PaMike · Dec 2, 2010

Do you think dirt could be causing something like this, or more of a mechanical problem? Kinda wondering if I oughta just put in a used valve and be done with it.

Anonymous-0 · Dec 3, 2010

If you took the rod side lines off(retract) and the boom wasn't up all the way, oil in the cylinder would shoot out of the cylinder when you extended the cylinders further. On double acting cylinders, the cylinder is always full of oil on both sides until they are at the limit of their travel. All the control valve does is basically move the oil from one side of the piston to the other. I think you may have a valve problem but not a cracked valve. I'd make sure the aux. hyd valve isn't sticking and causing an intermittent problem. A lot of skid steers never use the aux. hydraulics and they can get stiff from non use. Dave

MattE · Dec 3, 2010

It's a regenerative circuit so it is acting as it should. Problem either is spool is not shifting correctly or you have a bad check valve. probably the latter

RodinNS · Dec 3, 2010

Could be anything. I'd take it apart and see before going and buying a used one. Some simple work might fix it.
Another thing to consider... those foot pedals will disintegrate after a period of time... so it may simply be that the valve is not getting moved fully or as far as you think... tho normally the valves are self centering... so it should return to neutral and not drift... unless the linkage is sticking. Just take a close look at it.

Rod

mEl · Dec 3, 2010

Anti Cav circuits are use to send oil from one side of the cylinder that is retracting back into the pressure passage to suppliment pump flow, An example of this in a backhoe application would be if the boom was dropped quickly into a ditch and the cylinder was requiring more gpm than the pump could supply the anti cav valve would send retun oil from the other side of the cylinder to the side requiring more gpm. In our circuits it is not done within the section but sent out into the valves low pressure circuit to a poppet that can open to the hi pressure circuit if the pressure differential is high enough to open the regen check. So at this point you have lost the cylinder leaking back several inches and stopping problem? I left you a post on the old thread that you may consider, The 2500 lb thing has me fascinated if your packings are good. mEl

OT-Update-Need a Hydraulics Expert

Formerly PaMike

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CAROGATOR

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Heat Houser

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Formerly PaMike

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RodinNS

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Formerly PaMike

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Anonymous-0

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MattE

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RodinNS

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mEl

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