Loader Valve Leaking Down

[dieselscout80]

My TC45DA factory loader at time drifts down while I am using it.

Is this an indicator that the loader valve needs new o-rings/seals?

 

[Harry in Ky]

No. There are no O rings in the loader valve that have anything to do with holding up a load when spools are in neutral. Spool clearances and load checks do that. While your valve may play a small part in loader drift down, it's more likely a piston seal in one of the loader lift cylinders.

 

[Dman1981]

Easy check for cylinders loader all the way down do this cold and put down pressure so relief goes off for a minute or two at intervals and then touch cylinder where
Piston is if oil is bypassing will be warm to touch
Also can do same thing pull off hose cap it and see if oil shoots out same idea will need pan for oil though be careful if piston seal is totally blown lots of oil
That way you will know if it is a cylinder or a circuit relief valve.
Not all Loader valves have those though

 

[dieselscout80]

Thanks

 

[dieselscout80]

No. There are no O rings in the loader valve that have anything to do with holding up a load when spools are in neutral. Spool clearances and load checks do that. While your valve may play a small part in loader drift down, it's more likely a piston seal in one of the loader lift cylinders.

Sometimes when I start to move the loader control it drops a bit before it goes up.

That said based Dman1981‘s on post it sounds like I may have a cylinder problem.

 

[4570Man]

No. There are no O rings in the loader valve that have anything to do with holding up a load when spools are in neutral. Spool clearances and load checks do that. While your valve may play a small part in loader drift down, it's more likely a piston seal in one of the loader lift cylinders.

A leaking piston seal will significantly worsen a leaking valve but unless it’s pouring on the ground the fluid has to go back through the valve.

 

[Dman1981]

The other thing loader valves have is a load
Check it keeps the oil from leaking back thru so you don’t get the fall when you first crack it
Takes so much pressure to lift poppet off it seat then the pressure is more on lifting side so bucket or loader does not fall first

 

[rScotty]

Sometimes when I start to move the loader control it drops a bit before it goes up.

That said based Dman1981‘s on post it sounds like I may have a cylinder problem.

I don't see how the problem can be in the cylinder. Think about the loader control valve for a moment. Until you move the levers, the control valve is simply an on/off switch in the OFF position. In that OFF position with the the levers sitting in the neutral center position the control valve blocks all flow to and from the cylinders.

Now picture the cylinders. In order for the loader arms to drift down , the lift cylinders have to become shorter, which they can only do by forcing fluid that should be trapped inside the cylinders to go somewhere else. Without a leakage path through the control valve and back to the sump, the lift cylinders cannot shorten and the loader arms cannot drift down.

It won't hurt to look at the cylinders and do some tests, but I think you should also look at the loader control valve. If it is the type of control valve that has a built-in relief valve then that is where I would look first.

rScotty

 

[4570Man]

I don't see how the problem can be in the cylinder. Think about the loader control valve for a moment. Until you move the levers, the control valve is simply an on/off switch in the OFF position. In that OFF position with the the levers sitting in the neutral center position the control valve blocks all flow to and from the cylinders.

Now picture the cylinders. In order for the loader arms to drift down , the lift cylinders have to become shorter, which they can only do by forcing fluid that should be trapped inside the cylinders to go somewhere else. Without a leakage path through the control valve and back to the sump, the lift cylinders cannot shorten and the loader arms cannot drift down.

It won't hurt to look at the cylinders and do some tests, but I think you should also look at the loader control valve. If it is the type of control valve that has a built-in relief valve then that is where I would look first.

rScotty

Like you said the fluid has to leak back through the valve but a leaking cylinder seal will make the problem drastically worse. Instead of having to push a whole barrel full of fluid it just has to push the rods volume of fluid since most of it was allowed to bypass. It would also make the psi in the cylinder considerably higher since the same load is resting on less area.

 

[mikester]

My TC45DA factory loader at time drifts down while I am using it.

Is this an indicator that the loader valve needs new o-rings/seals?

No enough information. There is an acceptable leak down RATE. Are you talking about the loader dropping 4 feet in 1 minute or 4 inches in 1 hour? There is a difference. Quantify please. All hydraulics leak down.

 

[oldnslo]

I don't see how the problem can be in the cylinder. Think about the loader control valve for a moment. Until you move the levers, the control valve is simply an on/off switch in the OFF position. In that OFF position with the the levers sitting in the neutral center position the control valve blocks all flow to and from the cylinders.

Now picture the cylinders. In order for the loader arms to drift down , the lift cylinders have to become shorter, which they can only do by forcing fluid that should be trapped inside the cylinders to go somewhere else. Without a leakage path through the control valve and back to the sump, the lift cylinders cannot shorten and the loader arms cannot drift down.

It won't hurt to look at the cylinders and do some tests, but I think you should also look at the loader control valve. If it is the type of control valve that has a built-in relief valve then that is where I would look first.

rScotty

Scotty
Unless the relief valve is a work port relief it is not in the loader circuit and would have no effect on loader drift.

 

[dieselscout80]

No enough information. There is an acceptable leak down RATE. Are you talking about the loader dropping 4 feet in 1 minute or 4 inches in 1 hour? There is a difference. Quantify please. All hydraulics leak down.

Like 4” down in a 1-3 seconds.

 

[rScotty]

Scotty
Unless the relief valve is a work port relief it is not in the loader circuit and would have no effect on loader drift.

I agree with that.

 

[rScotty]

Like 4” down in a 1-3 seconds.

Now that is interesting.
Does it then hold for awhile and then repeat the sudden drop?
Will it eventually stop dropping?
And how does the amount of load in the bucket affect it?

I figure that when it drops like that your instinct is to move the lever and raise it back up. How does that work?

Oh, and is it just the lift arms or does the bucket try to uncurl or whatever at the same time?
rScotty

 

[Dman1981]

I don't see how the problem can be in the cylinder. Think about the loader control valve for a moment. Until you move the levers, the control valve is simply an on/off switch in the OFF position. In that OFF position with the the levers sitting in the neutral center position the control valve blocks all flow to and from the cylinders.

Now picture the cylinders. In order for the loader arms to drift down , the lift cylinders have to become shorter, which they can only do by forcing fluid that should be trapped inside the cylinders to go somewhere else. Without a leakage path through the control valve and back to the sump, the lift cylinders cannot shorten and the loader arms cannot drift down.

It won't hurt to look at the cylinders and do some tests, but I think you should also look at the loader control valve. If it is the type of control valve that has a built-in relief valve then that is where I would look first.

rScotty

So if a seal
Is blown it will displace
Oil from one side of cylinder to other also unless you hydraulic locking mechanism plus in forty five years don’t see to many valves that are totally leak proof
Reason for hydraulic locks on cylinders
Be pretty scary if you were a hundred feet in the air and cylinder or hose blew
Worked aerial ladder trucks a fire department also

 

[dieselscout80]

Now that is interesting.
Does it then hold for awhile and then repeat the sudden drop?
Will it eventually stop dropping?
And how does the amount of load in the bucket affect it?

I figure that when it drops like that your instinct is to move the lever and raise it back up. How does that work?

Oh, and is it just the lift arms or does the bucket try to uncurl or whatever at the same time?
rScotty

That’s with a load on it.

Not sure if it would stop as I was moving about 700 pounds on my pallet forks when it happened.

It will move up when I raise it, but it starts down before going up.

 

[rScotty]

So if a seal
Is blown it will displace
Oil from one side of cylinder to other also unless you hydraulic locking mechanism plus in forty five years don’t see to many valves that are totally leak proof
Reason for hydraulic locks on cylinders
Be pretty scary if you were a hundred feet in the air and cylinder or hose blew
Worked aerial ladder trucks a fire department also

Suppose that the cylinder is half way through its stroke and the piston is is somewhere near the center of the cylinder. The piston has a bum seal, so fluid can get past it, but fluid cannot get into or out of the cylinder because it is blocked by the loader valve being in the OFF position.

The thing to notice is that whatever oil is in the cylinder has nowhere to escape, and that the piston divides that fluid into two different volumes. The side with the ram in it has less fluid.

OK? Now what happens as the seal leaks or maybe we remove it altogether.

The cylinder can extend a little ways as fluid moves from the ram side past the damaged piston and into the new larger volume on the other side created as the cylinder extends. But the cylinder cannot ever compress, because to do that would mean oil on the large volume side would somehow be forced to occupy the smaller volume on the ram side. It is smaller on that side because the ram is already taking up part of the space, and we know that fluids don't compress. So seal or not, trapped oil can't move that way,

rScotty

 

[rScotty]

That’s with a load on it.

Not sure if it would stop as I was moving about 700 pounds on my pallet forks when it happened.

It will move up when I raise it, but it starts down before going up.

Doing it just once sounds like there is a possibility that air in the hydraulic fluid created a pocket of air in the lift cylinders - air WILL compress and can move where fluid cannot. Next time you get the hydraulic fluid working and up to temperature, take a look at the hydraulic fluid dipstick and see if the fluid is clear or foamy.

 

[oldnslo]

Like 4” down in a 1-3 seconds.

That sounds like a load check not seated. The load check is supposed to prevent oil from flowing out of a work port from load induced pressure into the pressure port. With open center system you need to move the spool far enough to block flow in the pressure port and direct it to the work ports partially shifted the pressure port with minimal pressure build up and can be connected to work port allowing the reverse flow if the check is not seated.

 

[rScotty]

That sounds like a load check not seated. The load check is supposed to prevent oil from flowing out of a work port from load induced pressure into the pressure port. With open center system you need to move the spool far enough to block flow in the pressure port and direct it to the work ports partially shifted the pressure port with minimal pressure build up and can be connected to work port allowing the reverse flow if the check is not seated.

I'm beginning to wish we had a hydraulic schematic. Does it have check valves? We need to know more about the configuration of the loader control valve(s). We've been assuming that it is the most basic type control valve - but it may not be.