Busted Cylinder Problem

So this is the cylinder on our intake. It’s a PHD brand OCG1 3/4 x 4 that I think came from Anydmark or first choice some time ago. As you may be able to see it is coming apart at the joint of the cylinder body and then end caps and is now leaking air. We will replace but we are looking to know how we ensure this wont happen in the future.

I think this may be happening because when the intake goes down it is a little violent and causes it to put some unwanted stresses on the cylinder. For note when we run into walls it pushes the intake up.

In my experience, Pneumatic cylinders hate being overextended. On our intake, we use hard stops so that the weight is not on the piston and instead on the stop. That way we never overextend the piston.

If a hard stop is not possible, i’ve also used steel cable to create a hard stop. This also has worked well for us.


Yeah, every time you smack it you loosen the crimp…

If you buy “cushion” cylinders they will be more resistant to this issue. Longer, though!

Adding a bit of compliance to your mounts could help, but that’s hard to pack into FRC spaces, especially on the extend. A rubber tube stop can work on retract.


I asked one of the Engineers your question. Here is the reply Mr. Cale R. from PHD, Inc. gave me to share with you.

Mr. Cale R.-
Two likely culprits here, and it may be a combination of both.

  1. Excessive impact on retract: As previously noted retract KE transmitting thru the cylinder can severely limit the longevity of the actuator. Providing external stops such that the intake stops/absorbs this energy (even if just a few millimeters shy of full cylinder retraction) should solve this.

  2. Excessive sideload: The ends appear very ridged allowing for only on degree of freedom. A force applied outside of that degree of freedom will expose the weak points, in this case those crimp connections. Should this force happen on extend/open, the resultant moment arm exacerbates the problem and I’d anticipate the failure mode you’re seeing at the cap end. If you’re able to accommodate with some mounting compliance (spherical clevis?) or other means of sideload mitigation, I think you’ll have it.

If you need a replacement cylinder, PM me and I should be able to help you out.


On the Bimba website they actually tell how you much energy their adjustable cushions can absorb!

Info: https://www.youtube.com/watch?v=lEjl-OhIKp8

I think the fact that you have a floppy (polycarbonate) intake design, but a rigidly mounted cylinder (no movement left/right as the intake flops about) will put a lot of excess loads on the cylinder body. The connection point that failed is exactly where you would expect it to fail if you put a sideways force on the intake mechanism over and over again. This happens every time you turn side to side with the intake out.

If you can make the cylinder mount at the base allow some swivel side to side so that the cylinder can move with the arm, I think it will last longer. The quickest way I can think to do this would be to severely oversize one of the holes on the mounting bracket that attaches to the pivot bolt. It only needs one side of that bracket to be functional, and the cylinder will have much more compliance to the intake moving side to side.

Actually, the best fix would be to just flip the cylinder the other way around, so a swivel ball end is attached to the frame pivot.

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If I had to take a guess just by looking at your CAD model I would say its excessive side load. Typically when we use cylinders we have learned to use spherical rod ends on the rod side of the cylinder and spherical or a compliant mount on the back end of the cylinder. Additionally it can be helpful that the cylinder is retracted when the intake is deployed (so its in it’s “strongest” configuration).


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