SpudFiles

Yeah, pretty much. That diagram is a tiny bit misleading though, let me edit it so if you build one, the diaphragm will work....

Argh.
I edited the diagram and somehow deleted it. Just make sure that the diaphragm is about 1 1/8 the size of the pipe ID. For example, use a 2.5" diameter diaphragm if you're using 2" PVC as a chamber.

got cha.. .....I might make a air rifle pellet gun.....I feel so noobish

to clarify, i will be using a 3" pvc schedule 40 endcap. If i cut say, 1 inch, off the opening to cut weight, will that help any?

thats a piston, but yea it will reduce weight.

any other tips to get a little better performance out of that style of piston? i plan on using a 1 inch sprinkler valve with it.

lube it up really well and have a really good bumper.

Fill it with foam or something to reduce pilot volume without increasing piston weight.

good ideas. keep em coming! im wondering what would be a decent bumper for 4"? i dont want anything ghetto like hose lol

hose wouldnt work any way, you need to find something that will absorb all the energy from it though.

what about those flotation pool noodle thingies? they might be 3" tho

I have decided to start building a coaxial diaphram valve cannon since I have just finished my small piston cannon. I have never built a diaphram before so I have a question: How many layers of inner bike tube do you need for the diaphram? I am building 2" diameter.

Don't use a bike inner tube. They are much too thin for this application. You need some tough 1/8" thick rubber sheet.

OK thanks. Cant you just use 2 or 3 layers though??

You can, but either it'll pop, get sucked into the barrel, or only one layer will get sucked back into the pilot area.

OK cool, I think I will just go look for some rubber at the store thanks for the help though.