IMHO, the standard to beat is McMaster-Carr's 4708K58, a bronze swing-check valve for a 2" pipe rated for 406degF and up to 200PSI. It costs $58.55, and unless somebody points out some problem, will probably be the way I go. It has NPT threads but that should be easy enough to adapt to standard radiator clamps by simply installing the appropriate adapters on each side.

I'm thinking this is plenty of margin for safety, given that I'll be using a pressure-relief radiator cap (no glycol and closed system for me), and if I go above 406degF I'm probably going to be concerned about WAY more than my check valves! (Fire!)

Any comments?

The only data I don't have is weight, but since it's bronze it can't be tiny - I figure a pound each to be safe. Two pumps plus two check valves is still lighter than the mechanical pump, so I'm still happy - if I can figure out where to PUT all this stuff! =)

So, how about it, Jim? Frankly, this falls within acceptable costs for me, especially since I won't be running with two pump controllers. I don't see that building a valve is the right way to go for me, but I'm interested in seeing / hearing about whatever you come up with.

Regards,
Chad