No cylindder pressure....

[mrcaptainbob]

Gees, this is going to be a messy job. No shutoff valves or filters to stop the gravity flow from the tank. An oil pan will be my friend.
Okay, let's suppose that I take that valve body apart. Is that even a wise thing to do? If I did that, what would I look for? Nicks? Some kind of deterioration some place? On the 'shuttle' or the body itself? Is there difficulty in reassembly? Chance of my nicking or scoring something?
So, what about that pump? Is it possible for it to pump intermittently? It hit high psi with an almost closed gate valve, but not knowing just how the internals work, well, I'm guessing and grasping here.
Is it possible for an air bubble? I did change the cylinder-return-hose-to-valve-body when the original burst. I did exercise the cylinder to expel the air. And the unit worked well for some time after that. Then, seemingly instantly, it just quit splitting.
Not afraid of any of the work, am mechanical inclined. Many rebuilt auto, tractor and mower engines rebuilt etc. And a fair machine shop in the barn.

 

[J_J]

Did you fully check out the cyl for bypassing.

If you almost closed off the pump flow and the pressure went up close to the rated value, it sounds like the pump is good.

Fully retract the cyl and remove the base end hose and try to retract some more and see if fluid pours out the cyl port, and if it does, the cyl seals are leaking.

If the pump is a two stage, it will probably start out at high flow and low pressure, and when the pressure gets to about 700 to 900 psi, the pump shifts to low flow and high pressure.

 

[Egon]

Can't really help on the valve but if you pull it apart things may become obvious.

 

[oldnslo]

Did you fully check out the cyl for bypassing.

JJ,
Good idea but captain has already done this. The problem seems to be in the directional control valve. With out having the valve in front of us it is a guessing game but it sounds like the casting is cracked or porous allowing flow to go from pressure to tank with very little restriction. He has an old republic (Teledyne republic) pump so not sure if if hi-lo or single stage. I can't remember much about these models.

Captain,
Tearing the valve apart may show you what the problem is. My guess is the casting is cracked or porous between the pressure port and tank port. If this is the case I doubt it would be repairable but it doesn't work now so tearing it apart could help confirm the diagnosis is correct before spending money on a replacement valve.

If the valve is mounted higher than the reservoir you shouldn't have to drain the reservoir to change the valve unless all of the swivel connections are below oil level.

 

[mrcaptainbob]

The pump is not a two stage, J-J. The tag lists but the one psi, plus I've never seen evidence of it changing power. As for verifying that cylinder seal.....Does it matter which direction it's checked? I verified the seal with the cylinder fully extended. Did that twice. Removed the return line at the cylinder and tried to force more extension and no oil came from the cylinder port. Putting the lever to retract the ram and gobs of oil came gushing from the hose. Would checking the opposite, as you suggest, show something different?
Egon, I hope y0ou're right. Surely nothing is obvious to me so far!
It just seems like there's a flow through somewhere and all the checks seem to come out okay. The pump blows a gate valve at 1800 or so, the cylinder does not appear to have an internal leak, and the relief valve, when over-shimmed, still does not provide pressure or relief at either extension or retraction. It does sound like a valve issue. I will check that by pulling the shuttle out and looking to see what the inside of a splitter control valve looks like. Always room for more edumacation.....

 

[Egon]

Just be carefull with those pressure checks. Sometimes the components turn into shrapnel.

 

[mrcaptainbob]

Well this was an effort in futility! Put a new valve on today. Brand new. The only difference between the old and new is the old had 3/4 in and out with 1/2 ports to the cylinder. All hoses are 3/4. The new valve had all four ports at 3/4. Although the cylinder in/out was a bit faster, there was not much difference in pressure. Still not enough to activate detent. There was just the slightest rise in pressure. The old at max out was 450, while the new is at 525 or so. I exercised the cylinder in/out at least a dozen times to evacuate the air and made sure to top off the hydraulic tank. So.....does a new valve need to be adjusted? Or is this pointing to ......an intermittent bad pump? Or....(open to suggestions..)

 

[mrcaptainbob]

About checking that cylinder.....Twice I extended the ram all the way out. Disconnected the hose on the ram end. Started it up and tried to extend the ram. No oil came from the port. Sounds like the cylinder seal is okay. But, is it possible that the packing inside closed off that port? Would it be better to block the ram at half extension and then disconnect the hose for the check?

 

[wdchyd]

Just pulling stuff apart is not a good idea.....you'll end up with multiple problems

You need someone with a flow load/meter to rule out pump flow and pressure before disassembling any components....otherwise you will just be spinning your wheels and digging in deeper

Sorry to be a broken record, but.........:confused2:

 

[J_J]

Your pump is bad.

If you say the cyl is good, and the cyl is what causes resistance to the flow to build up pressure, then one would have to assume that with a new good valve in the flow path, that the pump is not working correctly.

Recommend you take the pump to a hyd shop for testing.