FEL how long 'should' bucked remain up when parked?

[4570Man]

Yes shocks have oil and metering valves, and they also have gasses in them. Gasses are compressible, fluids are not, or not very much. Hydraulic cylinders have fluid in them on BOTH sides of the piston and its seals. If you push down on the rod of a hydraulic cylinder and try to stuff it into the cylinder that has fluid in both sides of the piston, it doesn't matter if the seals leak or not, or EVEN if there is not a piston in there any more, you just cannot shove that rod into that cylinder space that is filled with oil. You just cannot do it no matter how much force you place on that rod trying to compress that fluid in there. Don't overthink this, it is as simple as that.

Only if the end seals leak could you do it. I've come to the conclusion ( a few days ago) that the piston doesn't matter.

 

[k0ua]

Penny in a jar is not the same scenario. Because the volume of the penny, and the volume of the water inside the jar....do NOT change when you flip the jar around.

With a hydraulic cylinder, as you compress it and force the rod into the body of the cylinder.....volumes change. So instead of a penny in a jar, a better comparison would be to cut a hole in the lid of the jar, and get a ~1.5" wooden dowel rod. This dowel rod represents our piston rod.

Now put the rod in the jar and fill the jar clear full with water. Pull the rod out.....and you will notice the water level went down right? Now if this rod where tightly sealed to the jar....that air space would be vacuum. This is what happens when a bucket or toplink drift (extension)

Now take that same jar, and fill it clear full without the rod in there. Once clear full, shove the rod in there. What happens to the water? It overflows right? The EXACT same thing has to happen inside a cylinder. In order to compress a cylinder (shove the rod down inside there), the oil that gets displaced HAS to go somewhere. The only place it can go is either back through the control valve, or all over the ground via a leaky hose/fitting.

Now we know what it is like to try to be a teacher. :confused2:

 

[LD1]

That's where I messed up earlier. Try your jar of water experiment using a golf ball and fill the jar before the ball goes in. Water will have to spill before the ball can enter the jar. The only explanation I can think if for the oil filled shock is the cylinder wasn't filled entirely with oil and has air space. If a hydraulic cylinder also wasn't filled entirely with oil it could leak until the air space is used up. If the end cap seals of the cylinder leak the rod could leak in either direction.

So are you now in agreement that the cylinder cannot compress unless the oil is displaced out of the cylinder via a leaky hose/fitting, or back through the valve?

While it is true that there is incompressible fluid on both sides of the piston seal, the cylinder can still move if the seal is leaky; the total fluid, and average pressure, stays the same in the cylinder, but it moves from one side to the other past the seal based on force somewhere causing a pressure differential between the two sides of the cylinder. If the seal does not leak, this pressure diffrential can be maintained and the FEL (or whatever) doesn't move.
I think a leaky valve is likely a more common cause, though.
9 pages of discussion about how long FELs stay up and nobody mentioned Viagra yet???

Thats where you are wrong. The total fluid cannot stay the same within the cylinder. You are forcing a ~1" diameter chrome/steel rod down inside the body of the cylinder. Thus the cylinder now has less area for oil to occupy. Therefore, you cannot compress a cylinder without displacing oil.

It is also why cylinders retract faster than they extend, because it takes less oil on the rod side. Also why they have less power retracting.

 

[k0ua]

That's where I messed up earlier. Try your jar of water experiment using a golf ball and fill the jar before the ball goes in. Water will have to spill before the ball can enter the jar. The only explanation I can think if for the oil filled shock is the cylinder wasn't filled entirely with oil and has air space. If a hydraulic cylinder also wasn't filled entirely with oil it could leak until the air space is used up. If the end cap seals of the cylinder leak the rod could leak in either direction.

OK, congratulations, you have officially been moved over to the "got it" side. :thumbsup:

 

[comancheflight]

Wait - I think I have it with James and Abe experiment example.....
Let me see if I can put this into different language -
The if you put a jar of water on the table and it is completely full. If you drop anything (read penny) the amount of water that will overflow the jar will be the equivalent volume of water. If the jar would have been sealed you couldn't add the penny since you couldn't compress the water...so if a cylinder rod is extended you can shove it back in because you are ADDING the volume of the cylinder to a space already full and the oil can't be displaced....bingo

 

[k0ua]

So are you now in agreement that the cylinder cannot compress unless the oil is displaced out of the cylinder via a leaky hose/fitting, or back through the valve?



Thats where you are wrong. The total fluid cannot stay the same within the cylinder. You are forcing a ~1" diameter chrome/steel rod down inside the body of the cylinder. Thus the cylinder now has less area for oil to occupy. Therefore, you cannot compress a cylinder without displacing oil.

It is also why cylinders retract faster than they extend, because it takes less oil on the rod side. Also why they have less power retracting.

OK, if we ever get him to understand this, then we need to blow his mind with the explanation of "regeneration" as in the regenerative high speed dump function.

 

[LD1]

Now we know what it is like to try to be a teacher. :confused2:

Frustrating at times...yes. But I dont mind as long as it stays civil. Thats why I am here, to gain knowledge, as well as share knowledge and hopefully teach others a thing or two.

OK, congratulations, you have officially been moved over to the "got it" side. :thumbsup:

I havent moved his name yet, waiting of definitive confirmation

 

[4570Man]

So are you now in agreement that the cylinder cannot compress unless the oil is displaced out of the cylinder via a leaky hose/fitting, or back through the valve?


It could still leak out of the end seals onto the ground, but I'm in agreement that if a cylinder leaks down and oil doesn't end up on the ground the valve is the only source it could be leaking.

 

[comancheflight]

James you are good but officially have the FOS badge from previous post

 

[k0ua]

Wait - I think I have it with James and Abe experiment example.....
Let me see if I can put this into different language -
The if you put a jar of water on the table and it is completely full. If you drop anything (read penny) the amount of water that will overflow the jar will be the equivalent volume of water. If the jar would have been sealed you couldn't add the penny since you couldn't compress the water...so if a cylinder rod is extended you can't shove it back in because you are ADDING the volume of the cylinder to a space already full and the oil can't be displaced....bingo

fixed if for you.