Cylinder Leak Down test?

[rScotty]

Piston can bypass internally...

It can, but it doesn't help. I'll give it another shot. This is worth working on because it isn't easy to see and it is worth the effort.

For this we need a cylinder that doesn't leak where the rod goes into the cylinder..... but most don't leak there and since we've got one here so lets take that cylinder over and put it on our work bench. Take it apart and lets drill some holes right though close to the outer edge of the piston. Drill lots of holes. Maybe about a dozen quarter inch holes all around the face of that piston. That ought to do it. The piston looks like swiss cheese. You can see daylight through it. Dad is going to be really pissed, but hey this is science. There is no doubt that oil can flow from one side of the piston to the other side now. Reassemble it with the piston roughly in the center of it's stroke. Centering it doesn't really matter, but we gotta try to be fair to both sides of our cylinder....

Now with a little funnel we add oil while tilting the cylinder to make sure it is full of nothing but oil - oops, aw crap - first we have to block off the intake and exhaust ports. So we clean up the spilled oil and finish the fill and and Viola! We now have an experimental cylinder full of oil, and the ports are sealed with some NPT bore plugs we found in the plumbing box of spares and inside that cylinder now lives a piston shot full of holes that is going to amaze our friends.

Check me on this......We are sure that no oil can go in or out that we won't see, and with all those holes through the piston there is no doubt that the oil can flow from one side to the other inside that cylinder and it can mix and bypass however it likes. All freely and without any restriction.

OK. It is crunch time. Time to compress the cylinder and to our surprise we find that our rod won't move. "What the heck? The rod won't move!! What's going on?"

Well, we play with it a bit. And we find that by pulling with lots force we can get the rod to extend a few fractions of an inch.... but as soon as we let off it snaps back right to where it was just like there is a giant spring inside. Huh..... weird..... and it still won't compress at all. It just won't. We prop it up and jump on it, beat on it, and finally we wedge it under the loader bucket and really push down on it....but that rod end just will not go into that cylinder.

So now you tell me. What's going on?

rScotty

 

[Tx Jim]

Piston can bypass internally...

Yes and boom will stay where it's set if control valve holds pressure.

 

[kennyd]

It can, but it doesn't help. I'll give it another shot. This is worth working on because it isn't easy to see and it is worth the effort.

For this we need a cylinder that doesn't leak where the rod goes into the cylinder..... but most don't leak there and since we've got one here so lets take that cylinder over and put it on our work bench. Take it apart and lets drill some holes right though close to the outer edge of the piston. Drill lots of holes. Maybe about a dozen quarter inch holes all around the face of that piston. That ought to do it. The piston looks like swiss cheese. You can see daylight through it. Dad is going to be really pissed, but hey this is science. There is no doubt that oil can flow from one side of the piston to the other side now. Reassemble it with the piston roughly in the center of it's stroke. Centering it doesn't really matter, but we gotta try to be fair to both sides of our cylinder....

Now with a little funnel we add oil while tilting the cylinder to make sure it is full of nothing but oil - oops, aw crap - first we have to block off the intake and exhaust ports. So we clean up the spilled oil and finish the fill and and Viola! We now have an experimental cylinder full of oil, and the ports are sealed with some NPT bore plugs we found in the plumbing box of spares and inside that cylinder now lives a piston shot full of holes that is going to amaze our friends.

Check me on this......We are sure that no oil can go in or out that we won't see, and with all those holes through the piston there is no doubt that the oil can flow from one side to the other inside that cylinder and it can mix and bypass however it likes. All freely and without any restriction.

OK. It is crunch time. Time to compress the cylinder and to our surprise we find that our rod won't move. "What the heck? The rod won't move!! What's going on?"

Well, we play with it a bit. And we find that by pulling with lots force we can get the rod to extend a few fractions of an inch.... but as soon as we let off it snaps back right to where it was just like there is a giant spring inside. Huh..... weird..... and it still won't compress at all. It just won't. We prop it up and jump on it, beat on it, and finally we wedge it under the loader bucket and really push down on it....but that rod end just will not go into that cylinder.

So now you tell me. What's going on?

rScotty

But, put two cylinder in parallel as they are usually plumbed on the loader, what happens then?

 

[ROUSTABOUT]

Yes and boom will stay where it's set if control valve holds pressure.

No, you can plug both line ends of cylinder and as piston moves fluid just goes from one side of piston to the other as the rod compresses or extends.

 

[BeezFun]

No, you can plug both line ends of cylinder and as piston moves fluid just goes from one side of piston to the other as the rod compresses or extends.

This video demonstrates why that's not true if the rod is retracting. You're correct if the rod is extending.

 

[ROUSTABOUT]

This video demonstrates why that's not true if the rod is retracting. You're correct if the rod is extending.

All you gotta do is lose a cup of fluid so it has room to move. Best thing is run the tractor and if one cylinder is hot and one is not, rebuild them two. If you dont do both, you'll do the other in two weeks.

You're talking about the volume displacement that the rod causes. Hydrolocking.

 

[ROUSTABOUT]

It can, but it doesn't help. I'll give it another shot. This is worth working on because it isn't easy to see and it is worth the effort.

For this we need a cylinder that doesn't leak where the rod goes into the cylinder..... but most don't leak there and since we've got one here so lets take that cylinder over and put it on our work bench. Take it apart and lets drill some holes right though close to the outer edge of the piston. Drill lots of holes. Maybe about a dozen quarter inch holes all around the face of that piston. That ought to do it. The piston looks like swiss cheese. You can see daylight through it. Dad is going to be really pissed, but hey this is science. There is no doubt that oil can flow from one side of the piston to the other side now. Reassemble it with the piston roughly in the center of it's stroke. Centering it doesn't really matter, but we gotta try to be fair to both sides of our cylinder....

Now with a little funnel we add oil while tilting the cylinder to make sure it is full of nothing but oil - oops, aw crap - first we have to block off the intake and exhaust ports. So we clean up the spilled oil and finish the fill and and Viola! We now have an experimental cylinder full of oil, and the ports are sealed with some NPT bore plugs we found in the plumbing box of spares and inside that cylinder now lives a piston shot full of holes that is going to amaze our friends.

Check me on this......We are sure that no oil can go in or out that we won't see, and with all those holes through the piston there is no doubt that the oil can flow from one side to the other inside that cylinder and it can mix and bypass however it likes. All freely and without any restriction.

OK. It is crunch time. Time to compress the cylinder and to our surprise we find that our rod won't move. "What the heck? The rod won't move!! What's going on?"

Well, we play with it a bit. And we find that by pulling with lots force we can get the rod to extend a few fractions of an inch.... but as soon as we let off it snaps back right to where it was just like there is a giant spring inside. Huh..... weird..... and it still won't compress at all. It just won't. We prop it up and jump on it, beat on it, and finally we wedge it under the loader bucket and really push down on it....but that rod end just will not go into that cylinder.

So now you tell me. What's going on?

rScotty

Yes, but if you leave a cup of oil out and get it to move after it hits the oil, you've got a problem. You didn't have to drill holes, just remove the packing.

 

[rScotty]

Yes, but if you leave a cup of oil out and get it to move after it hits the oil, you've got a problem. You didn't have to drill holes, just remove the packing.

I thought about just removing the packing - or the O rings - depending on which one a particular piston uses. But decided to drill the holes in the piston instead. Partly for the visual, and also because the packing helps keep the piston tight in the cylinder bore. When the piston is tight it can't slop sideways which helps to keep the rod end seal from leaking oil out or air in.
rScotty

 

[Tx Jim]

But, put two cylinder in parallel as they are usually plumbed on the loader, what happens then?

Please explain if there's a difference in pressure holding capabilities between 2 FEL boom cylinders attached in parallel vs single cylinder if control valve isn't leaking internally. I can't determine any difference in my old feeble brain
Thanks, Jim

 

[LD1]

But, put two cylinder in parallel as they are usually plumbed on the loader, what happens then?

Same thing. Nothing will leak down due to cylinders.

No, you can plug both line ends of cylinder and as piston moves fluid just goes from one side of piston to the other as the rod compresses or extends.

Incorrect.

It still blows my mind how many people still do not understand this concept.....and further....people giving hydraulic advise and advise on cylinder rebuilding