check valve

[jitup]

Hello,
I was wondering if a check valve is needed after the valve stem of my piston cannon to keep it from triggering when I remove the filler.
originally I was going to use a ballvalve but I would much rather use a check valve of it is needed.

Also if a check valve is needed can some one shoot me a good link or explane how to make one? it needs to be able to connect to 3/4 pvc.

Thank you

BTW this will be the last post asking about stuff before I upload my 3" piston cannon!!!

[jackssmirkingrevenge]

It depends on the size of your pilot chamber and how tight a fit the piston is, but generally (and we're talking 3" here ) you won't need a check valve if you remove the filling connection quickly enough.

[jitup]

Ok, that is good!
one other question. How are diaphram valves size determined? is it by the actual size of the diaphram, or by the size of the outlet pipe?

[jackssmirkingrevenge]

As far as I know it's a measure of the size of piping they're meant to be connected to. A 3/4" sprinkler valve for example has a diaphragm several inches across.

[MrCrowley]

Ok, that is good!
one other question. How are diaphram valves size determined? is it by the actual size of the diaphram, or by the size of the outlet pipe?

Well pistons can be determined in size by the porting or the housing.

Generally most people use the housing diameter, because that gives us a better representation of the size of the piston. Though some people say both, i.e 3" piston housing with a 1.5" porting.

With diaphragm valves you probably can do the same, but the size of the diaphragm isn't as important, because diaphragms are far easier to make then a piston, you can just cut a sheet of rubber to any size you want.