Some design changes and new parts

In the course of pressure testing the air camber, I discovered that you can’t pressurize a quick exhaust valve from the cylinder side. I was eventually able to get it to seal by holding my thumb over the exhaust port, thus giving air some time to leak around the diaphragm into the “in” side. I was then able to slowly add air to the cylinder without it opening. Obviously that’s not a permanent solution.

I bought some new fittings from McMaster so I can put the fill valve on the in side. So that solves that problem.

Next issue: I think the piston back might seal too well in the pipe, therefore not allowing the air chamber to fill. I haven’t tested this, but as great as the o-ring seals have turned out, I don’t think I can count on any leakage. If too much pressure builds up behind the piston it could potentially bend the piston shaft, so I don’t want to risk it.

I’ll have to add a one way valve across the piston back. I could do it from the outside with banjo fittings, but I’m worried that a tapped hole in the pipe wall might be leaky. Luckily I think I’ll be able to fit a valve directly into piston back (it’s a 3/8″ thick disk).

These looked like exactly what I want, but the quote came back at $40 each. I could swing that, but eh.. Feels like a ripoff for something that could be as simple as a ball and spring.

Enter the ball and spring:


I think building it will actually be pretty easy. I originally wanted to retain the spring with a hollow set screw, but the fit would be very tight with the plate as thin as it is. Using the little aluminum plate will give me an extra 1/8″ to play with. I added a little spring (#9435K35), a delrin ball (#9614K22), and some #4 screws (#92949A105) to my order. Done.

There’s one last know problem. I’m not sure how to attach the rubber bumper to the cannon back.


I’m hesitant to use adhesive, because I don’t want the joint to degrade if the cannon sits in storage for years. I’m going for heirloom quality here.

I haven’t been able to think of a better method, so I’m going to give adhesive a shot. I feel like maybe I’ve just been using the wrong adhesives in the past, so I called up Loctite and asked what they recommend for this. I was actually able to talk to a person about it which is nice. The woman I talked to recommended #380 so I’ll try that. Hopefully I’ll get a pretty permanent bond.

I also bought a razor saw for 10 bucks on amazon to hopefully make cutting the rubber bumper easier. I tried with a razor blade previously, and it was just not having it.


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