Sprinkler valve not sealing properly

[ppoppers]

Hey y'all,

I have built pneumatic spud guns in the past, using this same set up, with no problems. But now I have 4 completed spud (well, t-shirt, actually) guns in my shop and none of their modded sprinkler valves are sealing properly.

When I am filling their tanks, I hear the sound of air whooshing (?) through a small opening, where the valve is not sealing all the way. It definitely is not the 'valve wide open' noise. However, when I open up the hole in the diaphram, that is normally used to bleed air out of the sprinker lines, the tank pressurizes fine. But when I try to fire, the cannon does not fire, all the air just leaks out the bleed hole, slowly.

Can you think of any reasons why my valve would not be sealing, when the port to bleed air out is sealed up?

I am using 1", Orbit watermaster, with the standard blow gun mod.

[Gun Freak]

Is it a jar top (chamber seal) or a normal (barrel seal) ? Pictures of the setup always help too

[irisher]

Is there a manual override? Sometimes those can accidentally get flipped open.

[motorfixer1]

First, welcome to spudfiles

However, when I open up the hole in the diaphram, that is normally used to bleed air out of the sprinker lines, the tank pressurizes fine.

When you say hole in the diaphram do you mean the manual pilot valve? Usually a screw type plastic knob that allows the user to let a small of water pass through the valve without actuating it fully. Sounds like this manual pilot valve is not seating or there is debris on the diaphram seat. Pics would certianly aid the situation. Hope this helps.