Loader leak down.

[J_J]

I wrote this for the PT machines, but it applies to any machine that uses loaders or BH.

Here is the main reason that the lift cyl will drift down even if the lift cyls are good.

Excerpt:

Most hydraulic valves are a metal-to-metal fit spool design, so do not depend on the cylinder setting dead still with a tandem center spool. If there are outside forces on the cylinder, it will creep when the valve centers.

Any metal-to-metal fit spool valve never fully blocks flow. With external forces working on the cylinder, it may slowly creep with the valve centered.

Well, you have the outside forces with the weight of the lift arms. Then add leaky cyl and down it drops before your eyes.

What does the metal to metal contact tell you about the leakage. Spool tolerance to bore tolerance.

It speaks to the quality of the hyd components a manufacturer wants in their machines.

They can brag about tight tolerance, but do you think the would brag about loose tolerance.

However, some of you say PT brags about how they really wanted valves that leak more than other valve competitors.

Their reasoning, is not valid.

They could say, they were purchased on price alone, and that might be true.

Need I say more, you have the facts.

My loader arms leak down over night, but if I need better, I have some needle valves that can be used.

If it leaks down after that, it has to be the cyl seals.

 

[LD1]

Nice writeup.

I know cylinder seals get blamed frequently for cylinder drift. Bit cylinder seals alone wouldn't cause it. There has to be something else leaking somewhere. Either a fitting, rod gland, or the spool.

There are different volumes of fluid on the two sides. You can totally remove the piston seals and if everything else is tight, there should still be no drifting. Picture a cylinder with no piston seals. Heck, no piston for that matter. To collapse (drift), toe rod gets shoved into the cylinder. The rod has to displace fluid. That fluid has to go somewhere. If it cannot, no drift.

 

[J_J]

With no load you would be correct.

The cyl will extend or retract is theres is a load on it.

 

[boggen]

the more i think about it, the more threads i remember of cylinder rebuilds. but, i rarely see threads about tearing apart a valve, putting in new seals/o-rings, possibly balls / check valves, and any springs within the valve. lots of different talks about type of valves, but not actually repairing them. i don't remember anyone replacing any sort of needle.

 

[J_J]

When people talk about rebuilding valves, they are talking about the spools that have spool seals on them, thinking that will help their valve. It might help if the spool is leaking to the outside, making a mess. A worn spool will bypass internally.

If your cyl wall are good, then new seals will greatly improve the functionally of the cyl.

People install good filters, say about 10 microns, and that gets rid of the large chunks. What they don't realise is that the smaller particles are what contribute to the wear on all metal parts, and there is nothing you can do about that unless you go to a bypass 1 micron filter and that will clean up the fluid over time.

 

[boggen]

a reference point, you say 1 mircon crud, someone might see that as carbon build up in a sense on inside of a engine cylinder. were the metal kinda looks burned in a sense. or perhaps a better idea might be, if you live on a well with hardwater, and having kitchen sink stains, bathroom sink stains, shower stall stains. from the hard water building up and then drying on the surfaces.

so why is it, that you see hyd systems. were hyd pump is constantly running, vs a on demand hyd pump. constant fluid flowing through every hyd valve, before the hyd oil finally reaches back to the pump. with on demand, the hyd pump maintains a pressure in the hyd hoses and valves, but the pump is not constantly running if it does not need to. i am scratching my head some. it does take HP (horse power) to pump the hyd oil constantly. just from friction alone of all the hoses, valves, connection points etc....

i would also think there would be extra wear tear... from hyd oil being heated up, from constantly being pumped non stop, and causing everything to heat up every time tractor is ran,

 

[LD1]

Shouldn't matter if there is a load or don't. For all intents and purposes, the fluid won't compress. Therefore, for the cylinder to drift, fluid has to go somewhere OUTSIDE the cylinder. Be it past the spool, or external leak.

Sure, without seals the performance would suck. The fluid would be allowed to leak past the piston and return through the other work port. But with valve in neutral, the fluid is trapped and the cylinder ain't moving.

 

[LD1]

Same reason crossover valves don't work on a DA cylinder. Difference in fluid volume. If you are leaking down, its a valve issue or external leak PR something external to the cylinder. If you are having poor performance or lack of power, that could certainly be a cylinder though.

 

[J_J]

The best way to test a cyl is to pressurize one side of the cyl and open the opposite port.

Pressurize the other sides of the cyl in case the seals leak in one direction only.

 

[dfkrug]

Shouldn't matter if there is a load or don't. For all intents and purposes, the fluid won't
compress. Therefore, for the cylinder to drift, fluid has to go somewhere OUTSIDE the cylinder. Be it past the
spool, or external leak.

You are correct. This is one of the reasons that I posted the other day about "displacement cylinders", which
are hydraulic cylinders that have no piston seals at all.

As you said, loader leakdown is in the valve if you don't have external leaks. If you can't see the leakdown
causing visible FEL motion, your valve is generally in-spec. Some are clearly better than others.