Hydraulic Piston twist

[scarecrow55]

If you have a clevis that is just screwed on and not locked, on the end of a piston rod. Could the rod twist and unscrew the clevis (the clevis can't rotate)?

 

[geoffthehammer]

If there is nothing to prevent the piston from rotating then it is a possibility however slight.

 

[SomeYahoo]

Most clevises that I have encountered are split and have a threaded fastener to cinch the internal threads tight around the external threads, reducing the risk of backoff.

I barely ever use them and haven't had one come apart yet.

 

[Barry1961]

I have seen cylinder rods unscrew themselves. This was mostly on high cycle lightly loaded applications. I have never seen a large cylinder rod end that was not locked with a jam nut or a type of thread locking compound like Loctite.

Barry1961

 

[EdDanzer]

Pistons try to follow the hone helix when the seal is under high pressure. Locking threaded fasteners in a hydraulic cylinder application is difficult. Jam nuts and thread locking compounds are not the best choices, as they frequently fail. Welded pin mounts seem the best. If it must be threaded, a split nut clamped, or a large dowel pin through the shaft and clevis seem the best. The push and pull forces combined with side loads tend to make the threads move between each other.

 

[scarecrow55]

Thanks guys, I'll lock it somehow

 

[Cockroach]

Use a thread lock, typical in the oilfield. Something like Bakerlok or equivalent would "glue" the mating pieces together. You apply heat, like from a blow torch or equivalent to break them apart.

I've used this extensively in the field, never a problem. The glue itself is like a Crazy Glue, so very strong. You can pick up a small bottle at any fastener supplier, inexpensive and practical.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada