WaterWar.net

http://www.youtube.com/watch?v=DG6own141z0
I haven't tried it out but theoretically it works.

Thank you for sharing, never paying $8 for PVC check valves again.

Wow. I mean, wow. I was this close to going out and buying those NPT threaded check valves. My only question is, where do I find acrylic balls like that?
Also, I wonder if the rubber ball version is any good for a homemade.

I would not trust the rubber balls alone in an APH. For a CPH, it depends on how much resistance your rubber is generating. A CPS 2000 runs at about 40 PSI?

This is better than WaterWolf's method. The ball allows you to keep the valve shorter. I don't like the threaded connections for check valves, though. Yes, they are reusable, but you're introducing 4 potential points of pressure loss in the area where holding pressure is arguably the most important. Obviously, the pump needs to generate more pressure than is in the PC(s), or else the 2nd check valve will not open. Thus, the region between the check valves must be the most rock solid in the entire gun. If a slip fitting can be found with a seat inside that is large enough for the O-ring, I'd rather do that. At 35 cents, who cares if the valve can't be reused?

You could use a reducer coupling instead of a threaded coupler. If you can't find one, you could always solvent weld, or epoxy, the threaded connection.

That is so epic. Now I just want to be able to increase the pump size in a stock gun and still have it work with the other internal parts.