Need Some Hydraulic Troubleshooting Help

[jinman]

With the cylinder extended there is approximately 14.9 cubic inches more oil in the blind end that will fit in the rod end. Now based on the pricipal that oil and the steel rod do not compress, where is this oil going to go?

Roy, I re-read your original post and you and I are agreeing except in the amount of retraction. I misread your post and agree with most of what you said. Even so, with the cylinder fully extended, how much oil is in the rod end? Isn't it zero? The seal is all the way against the gland nut, isn't it? With both the extend and retract ports plugged, but a leaky seal inside, the rod can be pushed against the "blind end" and fluid will leak by the seal and into the rod end until pressure equalizes across the leaking seal. That is more than half the cylinder's stroke length. The rod won't fully retract, but it will certainly retract a bunch. Whether that's enough to put his bucket on the ground probably depends on whether the bucket is flat or curled down. Since we are talking about the lift cylinders, I suspect your theory that the cylinders are not responsible is certainly well taken. If we were talking about the curl cylinders, they can fully extend with no problem whatsoever so that the bucket droops. However, since we are talking about lift cylinders, they should retract only partially.:thumbsup:

 

[oldnslo]

Yes depending on any unfilled volume in the rod end the cylinder will move until pressure is equalized, and yes this concept is hard to grasp.

NOTE: ALL of this is based on no leak path in either cylinder port. All Spool type directional valves leak, some more than others, so if they are connected this test will not be valid.

Roy

 

[J_J]

I totally agree with what has been said, about leaking down so that the cyl piston equalizes the pressure as I said before.

The only way I can see that the spools can cause the descent of the cyl's, is if both lands on the spool were bad. Then you would have a supply of fluid to fill the rod end, and somewhere for the fluid to go.

Again, with the weight of the lift arms and bucket pushing on the base end of the cyl, someone is saying that the valve spool will leak and cause all the fluid to leak out of the base end through the base end gland on the spool. This sounds good, except if the base end spool land is good, and does not leak,how does the fluid get out of the base end, and where is the fluid coming from to fill the rod end. If no fluid can get out the base end, and the cyl is good, then I don't think the cyl rod will move very much, if at all.

So with a lot of loader arms on the ground, what is the primary cause of the descent? Maybe both cyl and valve spool.

What I am saying,is that both lands of the spool would have to leak, to let fluid pass out of the cyl to the valve cavity, and for fluid to be able to get into the rod end via a worn spool land. Then the cyl would retract by gravity/weight.

Try this if you don't believe it. With a good cyl, and connected to a good valve by QD's, pop rod end QD, push the lever to make the lift arms drop, since there is no place for the fluid to go, what will happen? The relief valve will probably activate.

I would say the best way to check for cyl leak is to put pressure on the piston and open the cyl port, and push the valve lever to the max. Then reconnect that port and do the other one.

 

[oldnslo]

I totally agree with what has been said, about leaking down so that the cyl piston equalizes the pressure as I said before.

Try this if you don't believe it. With a good cyl, and connected to a good valve by QD's, pop rod end QD, push the lever to make the lift arms drop, since there is no place for the fluid to go, what will happen? The relief valve will probably activate.

Is this with the tractor running or off? With the tractor running your will definitely put pump flow over the relief and the FEL will lower.

With the tractor off the FEL will lower since you have know opened a path through the valve to tank.

I would say the best way to check for cyl leak is to put pressure on the piston and open the cyl port, and push the valve lever to the max. Then reconnect that port and do the other one.

Yes this will check the seals on the piston at both ends of stroke. Unfortunately it does tell you what condition the cylinder bore is in in the middle of stroke. I.e. is the bore scored or bellowed form a pressure shock.

 

[J_J]

Using a hyd hand pump, you can test both cyl and valve. Just fill the cyl rod end and connect the hand pump and pump up to about 500 psi, and see how long it holds. Do the same for the base end, extend the cyl and fill. Then do the same test. A piston may seal better in one direction than the other.

With the valve in neutral, connect the pump to the work port and pump up to about 500 psi. Test all work ports. You can then see the drops per minutes that the manufactures use to classify a valve as good or normal or needs repairing or replaced.

 

[J_J]

With the QD on the hose disconnected,

If there is no place for the fluid to go out of the cyl, the fluid will be locked in the rod end of the cy, and it can't lower.

Roy, I didn't understand this.

[ With the tractor off the FEL will lower since you have know opened a path through the valve to tank. ]

 

[oldnslo]

With the QD on the hose disconnected,

If there is no place for the fluid to go out of the cyl, the fluid will be locked in the rod end of the cy, and it can't lower.

Roy, I didn't understand this.

[ With the tractor off the FEL will lower since you have know opened a path through the valve to tank. ]

"JJ, this is copied from your previous post"Try this if you don't believe it. With a good cyl, and connected to a good valve by QD's, pop rod end QD, push the lever to make the lift arms drop, since there is no place for the fluid to go, what will happen? The relief valve will probably activate.

With the rod end QD disconnected you still have a flow path back to tank on the blind end.

If you mistyped, like I frequenly do, and you meant with the Blind end QD disconnected.

With the tractor running and pressurizing the rod end the loader should not move.

With the tractor off and shifting the valve If the piston seals are bad it will drift down when you shift the valve since you now opened a path for oil to escape from the rod end.

Roy

 

[J_J]

This is what I mean. With the lift arms raised, and engine running or not. If you separate the rod end QD, the loader will be locked in the up mode. There will be no fluid to push the rod back in the cyl . The weight of the loader alone might cause air to be sucked in through the rod seals.

Now, even if the tractor is on, and you want the loader to descend by pushing on the lever, the separated QD is not passing any fluid, even though the fluid can escape out the base end.

With the tractor off and the loader raised, there is nothing to cause the cyl fluid to move, and there is no or little fluid in the rod side.

 

[oldnslo]

This is what I mean. With the lift arms raised, and engine running or not. If you separate the rod end QD, the loader will be locked in the up mode. There will be no fluid to push the rod back in the cyl . The weight of the loader alone might cause air to be sucked in through the rod seals.

Now, even if the tractor is on, and you want the loader to descend by pushing on the lever, the separated QD is not passing any fluid, even though the fluid can escape out the base end.

With the tractor off and the loader raised, there is nothing to cause the cyl fluid to move, and there is no or little fluid in the rod side.

JJ,
with the rod end discconneted and you open the cap end to tank the FEL will lower since it will draw a vacuum on the rod. This will happen with the tractor on or off.