CO2 Check Valve

[fencer]

I don't think there is a special check valve. The reason for the check valve is to stop water from wrecking your soleniod. Mine looks like a simple diaphram...actually looks like an aquarium pump check valve. If you really want to get fancy you can buy a spring loaded check valve for 20 bucks or so. If you do, make sure it can lift off with a couple pounds of pressure( even 1 psi )