for flattop valves an piston, and the ICV.
1 full pump, like from 10.... yikes thats 10% loss just to crack the valve.
oy.... the 1377 valve doenst have the shelf like the 39x valve do to hang the ICV hardware on. Soooo... drill out the valve the create the shelf from the valve body,or drop a small it of tube in.......
And I'm going to suppose that the size and shape of the check valve itself has little bearing on the opening forces required.....
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