My FEL is bleeding down

[davesl708]

I guess the solution to the debate is to get a cylinder, remove the o rings from the piston then position the piston in the center of the cylinder, reassemble and refill both sides of the cylinder with oil, plug the holes and see if the piston can be moved in both directions.

I do not have a spare cylinder or I would do the test myself. If anyone is up to it a video would be great.

 

[LD1]

The syringe example is great. Leak down will occur past cylinder seals. As stated, with a bad seal the oil moves more freely from base to rod end under pressure inside the barrel. The first step in a loader leak down test is to disconnect from the loader valve to isolate cylinder leakage from valve leakage. We actually have a special stand for checking leak down on returned cylinders.

wrong

I guess the solution to the debate is to get a cylinder, remove the o rings from the piston then position the piston in the center of the cylinder, reassemble and refill both sides of the cylinder with oil, plug the holes and see if the piston can be moved in both directions.

I do not have a spare cylinder or I would do the test myself. If anyone is up to it a video would be great.

Yes great idea. Oh wait, a snow plow cylinder is exactly that. No piston seals. Just a loose fitting keeper ring to keep the rod from exiting when fully extended. And one less port to plug to.

Filled with oil, NO you cannot compress it.

Think about it. Instead of removing the piston seals, why not remove the whole piston, fill the cylinder completely full of oil and block the ports. You really think you can shove the rod into that cylinder (that is clear full of oil) without the oil having to go somewhere.

I have no idea why this is such a hard concept to grasp, especially for those on here that work in the hydraulic field and/or work on these things for a living. To answer JJ's question from a few weeks ago, it is no wonder so many cylinders get replaced because of leakdown.......its because everyone keeps repeating this same flawed concept of how cylinders work.

Edit: A question for those who keep insisting that the fluid will simply bypass the piston and cause leakdown.....do you at least understand that the volume on the rod side is less than the base end? Do you know why a cylinder extends slower than it retracts? do you know a cylinder develops less force retracting?

 

[CJONE]

wrong


Yes great idea. Oh wait, a snow plow cylinder is exactly that. No piston seals. Just a loose fitting keeper ring to keep the rod from exiting when fully extended. And one less port to plug to.

Filled with oil, NO you cannot compress it.

Think about it. Instead of removing the piston seals, why not remove the whole piston, fill the cylinder completely full of oil and block the ports. You really think you can shove the rod into that cylinder (that is clear full of oil) without the oil having to go somewhere.

I have no idea why this is such a hard concept to grasp, especially for those on here that work in the hydraulic field and/or work on these things for a living. To answer JJ's question from a few weeks ago, it is no wonder so many cylinders get replaced because of leakdown.......its because everyone keeps repeating this same flawed concept of how cylinders work.

Edit: A question for those who keep insisting that the fluid will simply bypass the piston and cause leakdown.....do you at least understand that the volume on the rod side is less than the base end? Do you know why a cylinder extends slower than it retracts? do you know a cylinder develops less force retracting?

+1 and then really confuse the issue and pull the cylinder out. I have ran into a few that did not have a keeper and would pull right out past the packing! CJ

 

[LD1]

I have ran into a few that did not have a keeper and would pull right out past the packing! CJ

Was that intentional or did someone forget to put the keepers in there?

 

[CJONE]

The cylinder was built like that [cheap] and the fixture limited the travel. CJ

 

[TJP89]

My take on this is that if the cylinder is closed off from the rest of the system, then no, the cylinder won't move. Maybe a little, as the fluid moves slightly, but not really. BUT, the tractor hydraulic system isn't pressurized when the tractor (and pump) are off, so as fluid settles, and there is room for the cylinders to retract. That's how I look at it, correct me if I'm wrong.

 

[kennyd]

My take on this is that if the cylinder is closed off from the rest of the system, then no, the cylinder won't move. Maybe a little, as the fluid moves slightly, but not really. BUT, the tractor hydraulic system isn't pressurized when the tractor (and pump) are off, so as fluid settles, and there is room for the cylinders to retract. That's how I look at it, correct me if I'm wrong.

BUT, if the valve is closed (in neutral) then the fluid still can't go anywhere, doesn't matter if the tractor is ON or OFF. The fluid will have to leak externally, or bypass the spool in the valve for the FEL to lower.

Like when people say "my FEL is bleeding down, even when the tractor is running" well the tractor running has nothing to do with it...it can't sense the FEL bleeding down and make it stay in one spot.

 

[TJP89]

BUT, if the valve is closed (in neutral) then the fluid still can't go anywhere, doesn't matter if the tractor is ON or OFF. The fluid will have to leak externally, or bypass the spool in the valve for the FEL to lower.

Like when people say "my FEL is bleeding down, even when the tractor is running" well the tractor running has nothing to do with it...it can't sense the FEL bleeding down and make it stay in one spot.

Yes, I forgot about the valve, obviously if its closed then there's no place for the fluid to go. Must just be the imperfect closed system.

 

[PILOON]

Can it be true that thousands are rebuilding their cyl to fix a leak down when it is the valve causing all the problem.

It just seems to me that a load placed on a leaking cyl will leak down. That load being the bucket and lift arms.

It does seem strange that people that rebuild their cyl don't have the leak down after rebuilding.

Few people on TBN have said that by replacing the valve that the leak down was stopped.

Same with the 3pt leak down. Few people are replacing their 3pt valves.

They all seem to do the cyl. Why is that.

Just saying.

I agree, the valve should be the obvious culprit but then could not a cylinder leak past the seals to the opposite side of the piston seals? Agree that inner seals should be a rarity and would be caused by filthy unfiltered fluid.

 

[RandyT]

I agree, the valve should be the obvious culprit but then could not a cylinder leak past the seals to the opposite side of the piston seals? Agree that inner seals should be a rarity and would be caused by filthy unfiltered fluid.

Yes, you can have leaking from one side of the piston seal to the other, but in a non leaking system, lets say the lower part of the cylinder has 2000 psi of pressure. You will get some seepage from one side of the seal to the other side until it also reaches 2000 psi, then the ram can't retract any further. You also have to take into account that any collapsing of the ram increases the volume occupied by the ram inside the cylinder. A 2" diameter ram that moves 1/4" will occupy an additional .75 cubic inches inside the cylinder. that same movement inside of a 2.5" diameter cylinder will decrease the volume below the ram by 1.25 cubic inches. so you can only leak .5 cubic inches of oil before the ram can't move anymore, which roughly amount to 1/8" in movement.