Weak Loader; won't stay lifted.

[npalen]

If the cylinders are leaking the oil still has to go through the valve to allow the loader to drift down. It is totally possible and likely that a cylinder is leaking but the flow still has to go through the valve. A couple simple tests are:

like others have recommended switch hoses to the curl circuit and see if the drifting slows or stops and does it lift normally with reving the engine?

another option is to Jack the loader up disconnect the quick disconnect on the cap end and then remove the Jack. If loader now drifts down the lift cylinders are leaking internally.

Help me understand what you're saying here. The fluid "behind" the piston doesn't have any place to go, does it? (Since there is less displacement on the rod side of the piston)

 

[oldnslo]

npalen,
If the cylinder drifts with the cap end hose blocked then oil is leaking past the cylinder seals and out through the valve that was left connected to the rod end. With both hoses disconnected and blocked then yes you are correct the cylinder would not retract.

 

[npalen]

npalen,
If the cylinder drifts with the cap end hose blocked then oil is leaking past the cylinder seals and out through the valve that was left connected to the rod end. With both hoses disconnected and blocked then yes you are correct the cylinder would not retract.

Okay, I was thinking that you meant the rod end where you were saying "cap end". Makes me wonder if some of these discussions include at least some amount of confusion about which "end" is meant because of no standard nomenclature. (Cap end, rod end, base end, blind end etc)

I tend to say base end and rod end but that doesn't mean I'm right.

 

[rScotty]

Hello all,
I own a 1996 50th Anniversary Zetor 4320. Runs like a sewing machine in a tub of warm butter. Anyway, the Bush Hog 2445 QT loader has been getting weaker with time, doesn't want to stay lifted unless I hold the stick down and rev the engine. There are no visible leaks on the cylinders. Reservoir is full of hydraulic fluid. . What should I check first? Thanks

If you do replace the control valve assembly that should take care of the loader drifting down so quickly. 2 spool control valves with PB and SAE threads are in the $250 to $400 range. Even a new control valve assembly will let a loader drift down over a few hours, but it will have tight enough internal clearances to slow the fluid from leaving the cylinders so quickly.

You said you want to check it yourself, and with the control valve assembly doing its job you can then add a pressure gauge on a hydraulic "T" fitting which will let you figure out if the cylinder internal seals are leaking or if the hydraulic pump has gotten weak....or both.

Hmmm....come to think of it, if your 3pt hydraulic circuit is independent of the FEL hydraulic circuit you could insert the pressure gauge on a "T" fitting back there to check the hydraulic pump right now.
Your shop manual should have a pressure vs RPM curve for that pump.

But it sounds so far like you are still going to need a new control valve to stop the FEL drifting down.

BTW, how is the power steering? Any clues there?

.

 

[LD1]

With just the cap end (base) QD unhooked, and if loader drifts, it indicates BOTH a faulty valve AND leaking cylinder seals. Which I suspect is the case here since the OP is actually complaining about TWO issues.....1. leak down and 2. weak loader.

The fact that the loader drifts is already indication of a leaking valve.

The question now is simply whether the piston seals are also shot

 

[azbinder]

Okay, I was thinking that you meant the rod end where you were saying "cap end". Makes me wonder if some of these discussions include at least some amount of confusion about which "end" is meant because of no standard nomenclature. (Cap end, rod end, base end, blind end etc)

I tend to say base end and rod end but that doesn't mean I'm right.

Yes, rod and base.

 

[azbinder]

Very rarely does a valve go bad. With what the OP is describing, a cylinder has an INTERNAL leak. If the piston seals are bad, oil will move from one side of the piston to the other without leaking any oil to the out side.

 

[4570Man]

All valves leak. The question is how much is acceptable. They don’t have any seals in them. It’s unlikely the valve is leaking a notable about more vs when it was new. Blown piston seals can’t be the sole cause of a leak down. Unless fluid is leaking externally fluid has to go back through the valve. BUT leaking piston seals will cause more rapid leak down and a reduced lifting ability. Possibly a drastic to complete loss in lifting ability depending on how bad the leak is. Leaking piston seals has my vote for the source of this problem. Assuming you have quick connectors on the hoses swapping the lift and curl hoses would be a good place to start troubleshooting.

 

[LD1]

Very rarely does a valve go bad. With what the OP is describing, a cylinder has an INTERNAL leak. If the piston seals are bad, oil will move from one side of the piston to the other without leaking any oil to the out side.

You seem to lack a basic understanding of how hydraulic cylinders work.

The cylinder CANNOT and WILL NOT compress unless fluid LEAVES the cylinder. Either external leak or back through the valve. PERIOD. It is NO DISCUSSING OR DISPUTING. Oil simply cannot and will not just "move" to the other side of the piston. You can drill holes in the piston, take the seals out, or even remove the piston in its entirety. The cylinder still will NOT compress or cause "leak down" without fluid leaving the cylinder

 

[LouNY]

You seem to lack a basic understanding of how hydraulic cylinders work.

The cylinder CANNOT and WILL NOT compress unless fluid LEAVES the cylinder. Either external leak or back through the valve. PERIOD. It is NO DISCUSSING OR DISPUTING. Oil simply cannot and will not just "move" to the other side of the piston. You can drill holes in the piston, take the seals out, or even remove the piston in its entirety. The cylinder still will NOT compress or cause "leak down" without fluid leaving the cylinder

In "theory" you are correct with most two way cylinders.
In operation I've seen cylinders with bad sealing rings that leaked down faster then the valve leakage was.
And double roded steering cylinders will do so often as with the rods going through the entire cylinder there is no volumetric difference regardless of where the piston is located.