SpudFiles

I just got finished putting my instructable for the launch it together and here is the video of the coaxial in action I have to get my big compressor going before I can fire it at greater than 40-50psi but here is a quicky video of its a 48 inch srd-21/sch80 golfball barrel in a 4" PVC chamber ( need to upgrade the vent valve to 1/2 it currently 1/4" and it takes acouple of seconds to fire.

http://www.instructables.com/id/S9GE1NZF6B7T09A/

[youtube][/youtube]

I would highly advise against showing people how to make a very unsafe cannon, but that's your decision, I suppose.

dude you need a waaaayy bigger pilot.Other than that nice gun.

How it it unsafe? I cant see any inherent deficiencies except maybe its made of pvc. But how it that diffent than any other launcher. And about the pilot I know 1/4 was all I had on hand.

its unsafe because you used DWV fittings on it.

the reducer is DWV, drain wast vent. its not pressure rated. (i hate bringing this up, it always starts a long disscussion)

it accually is ok for about 50 psi, but not much more. as long as you keep you face away from the muzzle (i.e., load before you pressureize) you should be fine.

also, its smart to keep the face mask on....

it is nonethe less a very good cannon, minuse the use of one bad part. also, if you dont have a bumper, you should add one.

DWV is about the ones I could find for the fittings, but I have seen them used for plumbing before and tap water has a pressure about 70psi. There is a bumper, though I probably forgot it in the instructable.

well be carefull and dont go over 50psi I have seen bad things happen with DWV fittings...... bad things

take it up to 70 psi then drop it (actually dont) it might very well hold 80 psi but if you drop it boom! Just be careful.

You've seen DWV used for plumbing before because that's what it is... drain, waste, and vent pipe. In other words, it's shit tube. It's not meant for pressure other than the natural hydrostatic pressure generated in normal applications.

If you went to Home Depot or some corner hardware store, you are not going to find any pressure rated fittings over about 2". You have to go to a serious plumbing store to find them.

I was not going to say anything- so i won't

DeathBlade wrote:DWV is about the ones I could find for the fittings, but I have seen them used for plumbing before and tap water has a pressure about 70psi. There is a bumper, though I probably forgot it in the instructable.

DWV pipe is not rated for pressurized water. If a contractor used DWV rated pipe or fittings in the water supply system an inspector would make'm tear it all out and redo it with pressure rated parts.

So, it really doesn't matter that household water supplies are 50~70 PSIG since DWV is not supposed to be used on the high pressure side of the system. DWV is used for vents (which carry no pressure) and drains which carry at most a few tens of PSI.

For drains, the pressure on the pipe is the hydrostatic pressure caused by the height of the column of water supported in the pipe. In English units, with water as the fluid, the pressure gradient is 0.4 PSIG/foot of water height. So, in a typical home plumbing system, the drain lines need to withstand something like a 20 foot water head, which is what the pipe might get if the connection to the city drain was plugged and a drain on the second story of a house was the only inlet/outlet to the system.A 20 foot water head is just 8 PSIG (20' x 0.4PSIG/') of pressure. So, DWV rating is grossly insufficient for a compressed air gun.

What do you think a pressure rated 2x4 inch adapter would cost? I'm going to go see if I can find one tomorrow, and I dont want to get ripped off.

Other than the DWV reducer and cleanout plug, It's a very nice gun. A 3" end cap would probably work better as a piston though.

When does the instructables launch-it challenge end? I might enter it if I had a chance, but I think that MrCrowley has already won it with the amount he advertises his golfball gun on other forums and Youtube.

This launcher is unsafe, but the vast majority of people on sites like Youtube and Instructables would probably go out and use DWV PVC anyway. Also, you need a smaller pilot volume and a larger+faster exhaust on the pilot .