Hydraulic Top Link Drawbacks

[murphy1244]

Where is this air coming from??

 

[MtnViewRanch]

Now wait a minute, I do have a port that say PB which i assume is "power beyond", what else do I need to be able to have a hydraulic top link?

Power beyond is only a source for the hydraulic fluid, you have no control, it is a constant flow. You use the power beyond line to feed an additional valve to be able to control-divert that flow to a cylinder. Now you are back up to the $1000 range for everything or piece meal it together yourself and save a few bucks.

 

[Kenneth in Texas]

Power beyond is only a source for the hydraulic fluid, you have no control, it is a constant flow. You use the power beyond line to feed an additional valve to be able to control-divert that flow to a cylinder. Now you are back up to the $1000 range for everything or piece meal it together yourself and save a few bucks.

ok i understand now

 

[Threepoint]

If the cylinder seal is compromised, You no longer have 2 separate channels on either side of the piston. It behaves as one chamber, therefore if there is a load applied to EXTEND the cylinder, a vacuum develops right away, and air is definitely pulled in around the rod glands. It is just the way it is, I've experienced it many times. the glands simply aren't effective at sealing a vacuum.
Entrained air is no doubt a factor, but doesn't account for a long cylinder that extends fully over time.
When a load is applied to retract a cylinder with failed seals, the rod can't move because oil would have to leave the cylinder to make up for the volume of rod entering the cylinder.

Arlen and dkrug, thanks for the further comments. Arlen's point about the two chambers becoming one once the piston seal begins to leak explains what I was missing in posts #135 #144 and "seals" the deal for me (sorry, couldn't help myself ). Once I visualize it as a single cylinder, then, no matter how small the drop of oil getting past the piston seal as dkrug says, the vacuum created by the downward pull of the raised implement on the rod causes air to enter the leaky gland seal just enough to compensate for the volume of that portion of the rod that is trying to leave the cylinder. That exchange of incoming air (which is immediately compressed to some degree by the internal cylinder pressure) for the exiting portion of the rod continues gradually until all load is removed from the rod, typically by the implement settling on the ground. I think I've restated that correctly now.