John Smith8N said: (quoted from post at 13:05:10 01/11/14)
"When we initially remove the support under the bucket the weight of the bucket is applied to the rod trying to pull it out of the cylinder. Oil is incompressible so if the seals are tight the oil pressure on the rod end side of the piston simply goes up offsetting the added force and the rod is held in place by the increase in oil pressure. In fact that trapped oil pressure will hold much much more than the weight of the bucket as long as the seals are tight."
True.
No, that can't happen. If the rod extends and the piston tries to move toward that end, The volume of oil displaced by the movement of the piston that goes past the piston seal is less than the volume of oil needed to fill the space created behind the piston. There's no rod on the back side of the piston so that space is larger. Air would have to be introduced to allow the piston to move.
It has nothing to do with pressure. It's volume. Take a double acting cylinder. Take the piston out and throw it away. Insert the rod halfway into the cylinder. Fill the cylinder completely with oil and cap both ports. There's no piston at all, so that's a big seal leak. Try to move the rod. You can't. You can't move it in or out. You cannot cap both ports to test for a piston seal leak.
OK. Just so happens the bucket cylinders on my Kubby are leaking internally and high on my list of things to fix. Here is my leakdown test.
Bucket rolled back and tied in place with that blue strap
Double acing cylinder full of oil and both ports tightly plugged.
Strap removed from bucket.
Weight of bucket immediately begins to pull rod from cylinder and stops once bucket hits the mechanical stops.
What happened? Keep in mind - pressure and volume are related.
TOH
This post was edited by TheOldHokie at 10:31:31 01/11/14 2 times.
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