If you're still going after using a camera flash circuit, have you thought of using the circuit as intended but replacing the flash tube with a spark gap? I can't remember where but I did see it done somewhere.

[basic camera operation]
When you take a picture, the shutter triggers a secondary ...

mattyzip77 wrote:Why not put that T that the schrader is in pilot side, saving time and modding???

The only reason I can think of not to do this is because it would increase the pilot volume. (I don't know how good a reason that is though)

@POLAND_SPUD
What is the difference between a 1/4" QEV and a 2" QEV then? Because this would theoretically work in that application too. It seems like a small air cylinder and a ball valve is much easier to manage than figuring out o-rings and a piston on a QDV. (I had the worst time fitting o-rings ...

You certainly could use a 3-way ball valve to do fill/fire. Semi-auto with a 1" barrel does sound pretty interesting, although it would use up so much air...

It would be interesting to find out what chamber, barrel, and pressure results in launching a tennis ball at reasonable serving speed, and ...

Just a thought:

It seems like you could buy a 1/4" QEV for a lot less than a 1" QEV. But a 1/4" valve doesn't help if you have a 1" barrel. (just looking at mcmaster, a 1/4" QEV is $10 cheaper than a 3/4" QEV)

Ball valves are much cheaper than QEVs, but they're slow, and spring loading only gets ...

Yeah I'll go dig one out of my closet :lol:

If you don't use epoxy you can still use a plastic bottle. Polyurethane-based adhesives do a better job of adhering to the plastic, and one of the most commonly used ones (in water rocketry, for gluing bottles together for longer pressure vessels) is PL ...

Every piston valve I've ever built has fully discharged in a fraction of the time it seemed to take in the videos... is that simply a characteristic of large valves?

I believe that has to do with the fact that he's emptying the entire tank through the 3/4" fitting at the top. The small size ...

In my experience, epoxy will ignore grease. It sort of pushes it out of the way. The only things I've found that it won't adhere to are polyolefins, commonly used to make heat-shrink tubing.

If that's the case, how do people cast epoxy pistons if grease doesn't work?

I know that epoxy has a hard ...

EDIT: Okay, okay, I admit it was a really, really bad choice to use a level. Sorry if I angered anyone. If it helps at all, the level shows no signs of damage and I promise not to do it again. :oops: (I would like to point out that my dad was present while I was doing this, so interpret that how you ...

How would that make male threads :?: :?: :?: I meant pouring epoxy around the greased bottle threads. That would make female threads.

The greased bottle would be inside the fitting, and I would pour epoxy between the bottle and the fitting. That way I would have a bottle-PVC adapter instantly.

I ...

Might I suggest hydro testing it? Just fill it with water and fill with air until it bursts. When it fails it should just split in half rather then spitting plastic at you.


All of the tests I've performed are with the bottle filled with water, since it's in-compressible and doesn't store energy ...

Threads don't do much of anything compared to roughening up the surfaces. The tensile adhesive strength of most epoxies is usually 4,000+psi.

Just my opinion: I still don't feel comfortable with a thin-walled plastic pressure vessel. I'll stick to my steel and brass, that has a calculable failure ...

Here is the most recent test video:

http://i281.photobucket.com/albums/kk240/aEx155/Air%20Cannons/th_0235a547.jpg

This test was at 150 PSI. The brick fell 4 feet. I edited the video to remove the bad drops of the brick, and in the end I got tired of resetting the bottle so I just started ...

Gun Freak wrote:You hit like a girl :flower:
Beat the crap out of it and see how much it can take! :violent1:

I don't think my parents or my neighbors would like to hear anything blow up, but I'll go drop some bricks on it and see what happens.

If you monitor the pressure and bleed it off when it becomes excessive, a source for high pressure is dry ice and water. I have used this in the past to do some pressure testing.

Do not ignore the test and become distracted while waiting for the pressure to build. Don't take a bathroom break and ...