I'll post pics later...
I'm used to working on a Pro-Flo 600, all of the benches I've used were equipped with Incline Manometers...
Which explains the (as Homer puts it) DOH!!!!

I've been "playing with" ping pong balls, model airplane spinners and acrylic tubing...

Has anyone tested the differences between flapper type and ball type check valves (Flow direction control valves)????