Pneumatic Cylinder damage

[somenerd]

Our team was experimenting with two pneumatic cylinders. We made a rookie mistake and champed too hard on the pneumatic cylinders, and now they both have a slight kink inside; No outside visible damage, but you can feel a slight indentation or bump when pulling the piston out and in.
We tested them (with no load) after we realized our mistake, and they still worked. We weren't planning on using these on the robot, and our mentors think they should still be usable.
Next meeting, we are going to check the actual force provided by the cylinders to see how its performance in terms of force has been affected. I would like to know of anything we should look out for.
Thanks.
BTW, would connecting the cylinders to a pneumatics system (compressor, dump value, air tank, etc) and filling it to a high PSI force the cylinder back into shape? Or would it exacerbate the problem?

[sanddrag]

Originally Posted by somenerd

BTW, would connecting the cylinders to a pneumatics system (compressor, dump value, air tank, etc) and filling it to a high PSI force the cylinder back into shape? Or would it exacerbate the problem?

Don't do this. If it's within the rated pressure of the cylinder, you'll see no effect. If you exceed the working pressure of the cylinder, you are creating quite a safety hazard.

Do you have a picture of the "slight kink" ?

[somenerd]

Originally Posted by sanddrag

Don't do this. If it's within the rated pressure of the cylinder, you'll see no effect. If you exceed the working pressure of the cylinder, you are creating quite a safety hazard.

Do you have a picture of the "slight kink" ?

OK, then I won't waste my time then. I wasn't going to fill it over 120 PSI or so.
No picture. You have to feel it when you pull the piston. You cannot see any damage to the piston from the outside.

[Tristan Lall]

If those are ordinary non-repairable cylinders like the ones Bimba has been providing for free for ages, you won't be able to do any rework with an FRC pneumatic system. The Original Line cylinders are rated to 250 psi with air, and the proof pressure is probably two or three times that (before something fails, which is likely to be the crimped seam that holds the aluminum ends to the stainless steel tube, provided that you've used fittings and tubing that will even work at that pressure). In any case, prior to failure, you're unlikely to get appreciable plastic deformation in the casing—much less the non-uniform deformation you desire.

The cylinder safety factors in place in FIRST are totally inconsistent with the rated pressure of the cylinders—but I presume that has something to do with other hazards of high-pressure air and the ratings of other components, rather than a realistic expectation of a catastrophic failure of a cylinder in a way that could expel debris. (At the pressures we deal with, any failure is likely to be ductile, and hence will absorb a lot of energy. Shrapnel is not especially likely. If penetrated, a cylinder will simply spew air rather than explode.)

[Al Skierkiewicz]

Although they seem to work now, Murphy has taught me they will fail you at the most inopportune time, i.e. your last match on Einstein.

[somenerd]

Ok, Thanks for the replies.
They are rather large cylinders, maybe 2'' bore with either 1.5' or 2' of stroke. We had no plans on using them on the robot this season, and was only using them to further experiment with a suction cup system.

[MarkoRamius1086]

If I may add a comment for many on this thread. It seems that you have realized your mistake, that is the best way to learn and move forward.

For the record however, I want to remind teams that putting force onto the piston (that is not parallel with the piston's motion) is a B-A-D, BAD, idea. I can almost gaurantee at one point or another all of the older teams has bent a piston shaft, mine included. Horizontal piston motions can cause damage to the pistons if you have weight down on it, or even by having a circular motion with too much mass on the end (our case in Lunacy). Bending a shaft (more so the smaller the shaft diameter gets) is easier than most people think.

Good Luck this season!