OK, I have this piece of sched 40 pvc pipe, about 8" in diameter, about 8 feet long. I want to turn it into an air powered TP launcher. Don’t ask why, because that’s classified, on a need to know basis. I’d really rather not use any type of flammables or combustables. Preferably, it would be powered from an air compressor, that has enough psi to run standard air tools, but unsure of the rated pressure. What we were thinking was, set a smaller piece of pvc inside the tube (just large enough for the TP), about 2 feet in, then pressurize the rest of the 8" pvc, and somehow, release that air into the smaller pvc, and launch TP rolls. Only looking for a 100’ to 200’ ballistic range. I guess my question to the esteemed dopers is, how to suddenly release the built up air pressure (some type of hand valve maybe?) and what type of psi do I need for said ranges? Any help from junkyard warriors or engineering types would be most appreciated, and we’ll throw your name on a “round” or to, if you’d like. Also, we’re looking for low cost measures. Thanks,
Do a search on ‘potato cannon’ or ‘spud gun’ (too busy to find you a good site right now). I think the part you need is call a sprinkler valve. What you want is basically you high-powered spud gun. You should find what you want fairly quickly as I have seen this sort of arrangement on several sites.
What you want is called a butterfly valve. But PVC pipe isn’t rated for use with compressed air, so I won’t encourage you any further.
P.S. Use a bungee cord attached to the handle of the valve to make it whip open quickly, and put the butterfly valve between the 8" and the barrel pipe.
I can’t personally attest to the effectiveness of this gun, but I did build something similar to the second gun in the series with parts cobbled together from Home Depot. Mine had a six-foot 2" barrel and a four-foot 3" pipe as an air tank. Boy, was that thing fun. With the pressure at 150 psi I could fire a 1" beam of wood through a car door, obliterate a melon at 50 yards, and once shot a 4 foot dart I made over 700 yards. Destructive fun for all!
Some PVC is indeed pressure rated. If yours is not (and at 8" it probably isn’t) don’t use it. 8" is way too big anyway. You need a solid seal between the projectile and the sides of the chamber. Find a small valve (hand operated or solenoid-sprinkler) , about 2" or 3", and reducing bushings that will connect it to whatever size pipe you want. Use an air chamber equal or large in size to your barrel. Wadded up toilet paper makes a good seal behind the shot. 100 PSI is a max, from my experience, and most compressors won’t give more than 125.
The best thing to do is spend half an hour in the plumbing section of Home Depot or Lowes and get a feel for what’s out there.
I have built something like this… a two inch barrel, four inch chamber of equal length, two 1 1/2 inch sprinkler valves. I’ve gotten quarter mile ranges out of it, with a 115 psi charge. Dangerous as hell, of course, and no one in their right mind would having anything to do with it. So I’m working on a metal version to handle pressures up to 1000 PSI. Don’t try this at home.
All PVC pipe is pressure rated but no PVC pipe carries an air pressure rating that I know of (in the US).
8" pipe is not ‘too big’.
You do not want a small valve. In fact, your valve should be as big as possible.
Solenoid piloted ‘sprinkler’ valves are designed to be slow opening to reduce water hammer in irrigation systems. They’re the worst valve possible for this application.
