Photoshop doesn't come standard on Windows. You can use Paint to save a JPEG in the newer versions, under save as you should be able to change the file type under the filename.

Didn't think of modifying the spring, not sure if it would make a difference in performance but i wouldn't mess around with it. Just in case you screw it and the whole valve up.

Body filler is no where near as good at bonding PVC as it only fills the gaps and unlike PVC glue doesn't chemically join the pipe. Acetone can be used as primer on PVC, I do the following before glueing a joint; Clean both surfaces with methylated spirits and then prime with acetone then glue and j...

The pressure on both sides of the diaphram in the sprinkler valve is equal. Modifying the diaphram makes no difference and can hinder performance if you screw it up.

According to that site the cannon you linked to is powered by butane.

An easier way to make hydrogen under pressure is to take a metal chamber and add some HCl (Hydrochloric Acid) and then add Aluminium or Magnesium through a screw on end cap and then screw the end cap back on and wait about 30 secs - 1 minute depending on chamber size and voila.

Viper do you understand the concept of kicking up a dead topic.

It is going to be pretty hard to move that valve because of the pressure acting on one side. Are you going to have a schrader on the side of the coke bottle or are you going to fill it using a different method?

EDIT: Damn KVINCEO beat me to it.

If he is planning on storing the hydrogeb somewhere then it is seriously dangerous. If he purged his chamber with CO2 or another non-flamable gas then the risk of explosion would be averted. But I just can't see any advantages of using hydrogen over helium in a lighter than air pneumatic.

Good point, having lots of hydrogen around isn't a good idea.

Benny he is talking about using it in a pneumatic.

You can buy helium easily at party supply stores, hydrogen is not so easy to obtain. There are certain methods that will work but I reckon that helium is good enough for ligher than air cannons.

Get the lighter refill cans and then just pull one of the nozzles down by hand or with pliers and the butane will come out.

That is alot of money, try going to a different hardware store. I get mine from a place called GasWeld propane is AU$8 MAPP is AU$10.

Over here in Aus Propane is only like $8 a cylinder, are you sure it's that much in NZ MrCrowley. At that price you should be able to buy a BBQ tank full of propane.