Weak Loader; won't stay lifted.

[azbinder]

Contrary to what most people believe, a bad piston seal WILL cause leak down or drift. Oil will pass from one side to the other WITHOUT leaking oil to the outside. One way to check if a bucket cylinder has an internal leak is fairly easy.

1- Raise the loader high enough to dump the bucket to it's fullest.
2- Shut off engine and release pressure on the bucket. Move bucket lever back and forth a couple of times.
3- Disconnect BOTH hoses at the rod end fittings, NOT base end.
4- Start engine and gently apply pressure to the DUMP lever and watch for a large amount of oil to "squirt" out.
5- If oil "squirts from one cylinder then that cylinder piston seal is leaking.

The lift cylinders can be checked somewhat the same way. You would have to block the loader up prior.

 

[LD1]

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.

To what 4570Man eluded to....

YES, all valves have internal leakage. How much that is acceptable depends on the valve. But the "tolerance" most manufactures use is a given volume over time at a certain pressure. Something like 2 ounces per hour at 1000psi.....exceed that and the valve is considered worn. (not real numbers but just an example).

While a faulty cylinder seals will NOT cause leak down (that is the valve)....they CAN make the problem MUCH MUCH worse by 2 reasons...

1. instead of fluid only trying to escape out the passage in the valve connected to the base port....if the seals are worn fluid can now excape out the rod side passages of the valve. 2x as much room to leak past internally in the valve.

2. you are increasing the pressure in the cylinder since the static weight of the bucket is acting on a smaller area.
Example.....an average loader will show about 500psi static in the base port just to support its own weight. If said loader has 2" cylinder with 1" rods....That means the empty static weight of the loader is trying to compress the cylinders with ~1600# of force....which in turn...with a 2" piston....generates ~500psi of back pressure on the valve spools.

Now if the seals are shot....that same 1600# of static empty loader force on the cylinder translates to ~2000psi back pressure on the valve spool.

So....doubling the passages in the valve that fluid can escape by adding the rod end port as an escape route, as well as increasing the static pressure by a factor of 4 are why leaky seals can and do make a loader drift down FASTER. But they arent the only problem if you are experiencing drift at all.

 

[LD1]

Contrary to what most people believe, a bad piston seal WILL cause leak down or drift. Oil will pass from one side to the other WITHOUT leaking oil to the outside. One way to check if a bucket cylinder has an internal leak is fairly easy.

1- Raise the loader high enough to dump the bucket to it's fullest.
2- Shut off engine and release pressure on the bucket. Move bucket lever back and forth a couple of times.
3- Disconnect BOTH hoses at the rod end fittings, NOT base end.
4- Start engine and gently apply pressure to the DUMP lever and watch for a large amount of oil to "squirt" out.
5- If oil "squirts from one cylinder then that cylinder piston seal is leaking.

The lift cylinders can be checked somewhat the same way. You would have to block the loader up prior.

The first part of your comment in bold is flat out wrong.

The second part about testing a curl cylinder is correct

 

[azbinder]

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

Oil CAN and WILL "move" from side of the piston to the other. Piston seal "bypass" leakage is far more common that valve internal leakage. In over 50 years of repairing tractors and equipment, I can count on one hand how many valves I've replaced due to internal leakage, while piston seal would require me to take off my shoes. Just saying, internal leakage on control valves is RARE. Not saying that it doesn't happen, just not likely.

 

[LD1]

Contrary to what most people believe, a bad piston seal WILL cause leak down or drift. Oil will pass from one side to the other WITHOUT leaking oil to the outside. One way to check if a bucket cylinder has an internal leak is fairly easy.

2" cylinder, 1" rod, 24" stroke

Extend cylinder fully.....(raised loader fully)....cylinder contains 41.5 ounces of oil.

ᴨr² x 24 = 75cu in of volume. 75/ 231 = .324 gallons. .324 x 128 = 41.5 ounces of oil

Now for the cylinder to drift, the 1" rod has to enter the cylinder. Same cylinder fully retracted contains 41.5 ounces of oil MINUS the volume of the rod.

1" rod 24" long is 18.84 cu inches = 0.081 gallons = 10.5 ounces of oil.

So the retracted volume of oil is about 25% less than extended.

Tell me.....if it didnt leave the cylinder, just where did that 10.5 ounces of oil go that the rod just displaced???

 

[LD1]

Oil CAN and WILL "move" from side of the piston to the other

Not without leaving the cylinder it wont.

Piston seal "bypass" leakage is far more common that valve internal leakage.

Agreed

In over 50 years of repairing tractors and equipment, I can count on one hand how many valves I've replaced due to internal leakage, while piston seal would require me to take off my shoes. Just saying, internal leakage on control valves is RARE. Not saying that it doesn't happen, just not likely.

This isnt about how long you have repaired tractors or how many of each type repair you have made. The fundamentals remain the same.

As I mentioned earlier.....bad seals WILL accelerate loader drifting down. And repairing them may bring loader drift back to an acceptable level and people just "assume" that the seals were the issue.

 

[PILOON]

I always had my FEL 'leak down' but simply learned to lived with it.
Later I had a pump coupling issue that required servicing when I discovered the pump shaft seal was damaged from shaft corrosion.
I cleaned and polished the pump shaft and installed a new seal, (actually 2 as there was space for a second).
That was the end of my leak down issues.

 

[rScotty]

As I mentioned earlier.....bad seals WILL accelerate loader drifting down. And repairing them may bring loader drift back to an acceptable level and people just "assume" that the seals were the issue.

That's right. And it's a good explanation about what is actually accomplished when cylinder seals are replaced.

There is a lot of misunderstanding about cylinder hydraulics.

rScotty

 

[LD1]

That's right. And it's the basis for a whole lot of misunderstanding about cylinder hydraulics.

rScotty

Thats evident everytime one of these "loader leak down" threads come up.

Im frankly still amazed about how so many purported tractor mechanics and hydraulic experts still think oil can simply bypass the seals in a retracting cylinder and never leave the system. And will argue till they are blue in the face and still, the light bulb never comes on.

I really do wish I had a better way of explaining it.....a way to flip that light switch without so much effort, analogies, and explanation.

 

[rScotty]

I really do wish I had a better way of explaining it.....a way to flip that light switch without so much effort, analogies, and explanation.

Do NOT give up! The light bulb will come on. It did for me, it just took a while. I was in my mid 40s before it did for me. And had been a successful mechanic for 20 years.

rScotty