I got a video posted on youtube showing how...
the pumps and the flapper check valves and ...
... the combiner box that was made works. The idea behind the combiner box is that both pumps pump into it and .....
..... there are separate outlets from it going to.....
..... the two separate intercoolers. If one pump fails the remaining pump would still pump to both intercoolers. The pumps don't have internal check valves so the check valves in the box don't allow water to just be pumped back through the dead pump if there is one.
In the test I ran one pump only and then the other pump only and then both pumps together. The intercoolers hold about 1/2 gallon of water and with both pumps running that water is being cycled over 20 times a minute through the intercoolers.
Here is the youtube link...
http://www.youtube.com/watch?v=Zqb60NgxpxY&feature=youtu.beSum