My First Pneumatic - Mortar
Posted: Wed Apr 28, 2010 9:07 pm
This is the first pneumatic cannon I have built and bothered to post on spudfiles. I built one rather ghetto design with the chamber and firing mechanism on this before as a rifle-style cannon, but that was deconstructed and upgraded to build this for a school-related project to shoot ping-pong balls. It exceeded expectations.
Valve: Tee piston valve- 3/4" piloted by 1/2" ball valve, seals to 1/2" street elbow inside bushing- notes below on valve
Chamber: 3/4" 18" galvanized steel
Barrel: 1-1/2" 24" aluminium
I know the C:B ratio on this is absolutely terrible, but that's not really the focus of this cannon. It's a mortar, not a cannon. In a few days the barrel and attachment to the firing mechanism will be decommissioned in favor of a 3/8" barrel.
Notes on tee piston valve: I constructed a rather creative piston in the hopes that I could create a design that would work on a piston hybrid. Well, it could but I won't be using it. It works because it does in fact seal to the inside of the 3/4" brass nipple it sits inside of while sealed to the barrel. It does NOT work because after firing at about 100+ psi., it slams back into the 3/4"-1/2" adapter with such force so as to lodge itself firmly inside, requiring a lot of force with a pair of pliers to remove it for the next shot. I do know that the piston is sealing to the inside of the nipple because when I add more pressure to the chamber the pressure gauge jumps, then settles back down to a more reasonable increase, as the air forces its way past the neoprene washer. The advantage to this? The pilot volume is absolute. No pressure is lost from the chamber when I pilot the valve.
Because of this, ear protection is strongly recommended when firing. The first few shots left my ears ringing, but I learned my lesson quickly.
Comments and suggestions are welcome, but please none criticizing my C:B ratio.
Damage pics may follow, but are rather hard to acquire.
EDIT: If you have suggestions on cushioning the piston as it moves back, please suggest.
Edit by MrCrowley: Your previous title had the impression that your cannon was the first pneumatic cannon on Spudfiles. Just wanted to remove the confusion. Thanks.
Doh! Sorry.
Valve: Tee piston valve- 3/4" piloted by 1/2" ball valve, seals to 1/2" street elbow inside bushing- notes below on valve
Chamber: 3/4" 18" galvanized steel
Barrel: 1-1/2" 24" aluminium
I know the C:B ratio on this is absolutely terrible, but that's not really the focus of this cannon. It's a mortar, not a cannon. In a few days the barrel and attachment to the firing mechanism will be decommissioned in favor of a 3/8" barrel.
Notes on tee piston valve: I constructed a rather creative piston in the hopes that I could create a design that would work on a piston hybrid. Well, it could but I won't be using it. It works because it does in fact seal to the inside of the 3/4" brass nipple it sits inside of while sealed to the barrel. It does NOT work because after firing at about 100+ psi., it slams back into the 3/4"-1/2" adapter with such force so as to lodge itself firmly inside, requiring a lot of force with a pair of pliers to remove it for the next shot. I do know that the piston is sealing to the inside of the nipple because when I add more pressure to the chamber the pressure gauge jumps, then settles back down to a more reasonable increase, as the air forces its way past the neoprene washer. The advantage to this? The pilot volume is absolute. No pressure is lost from the chamber when I pilot the valve.
Because of this, ear protection is strongly recommended when firing. The first few shots left my ears ringing, but I learned my lesson quickly.
Comments and suggestions are welcome, but please none criticizing my C:B ratio.
Damage pics may follow, but are rather hard to acquire.
EDIT: If you have suggestions on cushioning the piston as it moves back, please suggest.
Edit by MrCrowley: Your previous title had the impression that your cannon was the first pneumatic cannon on Spudfiles. Just wanted to remove the confusion. Thanks.
Doh! Sorry.