My FEL is bleeding down

[arlen4720]

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.

Like has been said many, many times before....if a cyllinder is EXTENDED, it can't retract without some oil leaving the cylinder. The volume of oil that has to exit the cylinder has to be equal to the volume of the rod that is entering the cylinder as it retracts. It's just that simple.
Many single acting cylinders don't even have piston seals.
Consider this: Fill a jar to the top with water, then shove a dowl into it. Does the jar over flow? Is the volume of water overflowing equal to the volume of rod that was inserted?
Next put a tight lid on the jar, and put a hole in the lid, with a nice tight fit to the dowl. Do you think you could shove the dowl down into the jar with it full of liquid? Would it be safe to say that if the dowl moves down into the jar, that water would have to come out of the seal around the dowl?
Would it be safe to also say that if you have an extended hydraulic cylinder full of oil on both sides of the puck, and both ports capped, that the rod could not retract into the cylinder without oil leaving the cylinder?

Bucket curl cylinders and 3 point cylinders are different in the way that they are typically arranged on the machine, in the fact that they RETRACT to lift, so the load and gravity are trying to extend them. As the rod extends in a cylinder with bad seals, it creates a vacuum on both sides of the puck. Since the seals are bad in this example, you really have one chamber. The rod seals are not effective at sealing a vacuum and air is pulled in to make up for the volume of the rod as it leaves the cylinder.
I will challenge anybody to refute this logic. Also, I invite anyone with a settling loader boom to unplug the quick connects. As sure as the sun will rise tomorrow, that boom will not settle any further; of course I am stipulating that there is no external leakage of oil in the system.

 

[LD1]

Like has been said many, many times before....if a cyllinder is EXTENDED, it can't retract without some oil leaving the cylinder. The volume of oil that has to exit the cylinder has to be equal to the volume of the rod that is entering the cylinder as it retracts. It's just that simple.
Many single acting cylinders don't even have piston seals.
Consider this: Fill a jar to the top with water, then shove a dowl into it. Does the jar over flow? Is the volume of water overflowing equal to the volume of rod that was inserted?
Next put a tight lid on the jar, and put a hole in the lid, with a nice tight fit to the dowl. Do you think you could shove the dowl down into the jar with it full of liquid? Would it be safe to say that if the dowl moves down into the jar, that water would have to come out of the seal around the dowl?
Would it be safe to also say that if you have an extended hydraulic cylinder full of oil on both sides of the puck, and both ports capped, that the rod could not retract into the cylinder without oil leaving the cylinder?

Bucket curl cylinders and 3 point cylinders are different in the way that they are typically arranged on the machine, in the fact that they RETRACT to lift, so the load and gravity are trying to extend them. As the rod extends in a cylinder with bad seals, it creates a vacuum on both sides of the puck. Since the seals are bad in this example, you really have one chamber. The rod seals are not effective at sealing a vacuum and air is pulled in to make up for the volume of the rod as it leaves the cylinder.
I will challenge anybody to refute this logic. Also, I invite anyone with a settling loader boom to unplug the quick connects. As sure as the sun will rise tomorrow, that boom will not settle any further; of course I am stipulating that there is no external leakage of oil in the system.

I have no idea why this is such a hard concept for some to understand.

 

[davesl708]

On a two way cylinder you can remove the O rings on the puck and the cylinder can be extended and retracted due to the lack of seal between the two ends of the cylinder. The fluid moves back and forth flowing around the puck.

If the FEL arms are raised and the O rings are bad fluid will leak by and the FEL will lower. The fluid is simply moving from one end of the cylinder to the other.
A good example of this is your power steering cylinder. If the O rings wear out the steering will feel like it is floating when you are driving for a short time due to the pressure equalization on both sides of the puck. As soon as the pressure builds on one side of the piston it will move and you can steer.

 

[LD1]

If the FEL arms are raised and the O rings are bad fluid will leak by and the FEL will lower. The fluid is simply moving from one end of the cylinder to the other.

The fluid can "try" to move from one side to the other. But since there is different volumes from rod side and base side, SOME fluid has to EXIT the cylinder somewhere for the cylinder to retract.

This can only be in the form of an external leak (hose, gland seal, coupler, etc); or from a spool valve leaking by letting fluid return to tank.

 

[arlen4720]

On a two way cylinder you can remove the O rings on the puck and the cylinder can be extended and retracted due to the lack of seal between the two ends of the cylinder. The fluid moves back and forth flowing around the puck.

Think about what you are saying here. The volumes are different on each side of the puck. How do you account for that?
In the case of the steering cylinder the valve opens pressure to one side of the cyllinder, and the valve allows the other side to go to tank. If the seals are bad, fluid just blows through and can't exert force on the puck. That is not the same as a loader boom settling with a static load when the valve is centered.
Read over the logic in my previous post, and think about it.

 

[arlen4720]

I have no idea why this is such a hard concept for some to understand.

I think they view us as the dumb ones:laughing:

 

[J_J]

Prince Hydraulics > Support > Loader Valve FAQ

 

[J_J]

That is not the same as a loader boom settling with a static load when the valve is centered.

It is not a static situation with a load on the cyl such as a couple of hundred lbs.

Just for the h*ll of it, take a syringe and remove the plunger and close off the needle end.

Now, cut the o-rings or remove the o-rings on the barrel and fill the tube with water.

Now press on the plunger and see if the fluid in the tube will pass to the open side of the syringe.

Do you think the water will transfer?

 

[arlen4720]

Prince Hydraulics > Support > Loader Valve FAQ

While that is useful information, it doesn't refute any of the points that I made. In fact, in step 7 it says to mark the boom cylinders and measure the amount that they settled, calculate the volume, and says that is the amount of oil leaking by in the valve. They don't mention that bad seals could be the cause.

 

[arlen4720]

It is not a static situation with a load on the cyl such as a couple of hundred lbs.

It is a static load in the sense that everything is at rest and pump pressure is not being directed to the cylinder. But, I feel you are trying to divert attention away from the simple principle that I'm trying to explain. If you agree with my logic great, if not, I would love to hear your logic on how you disagree.