I just took apart a V&V Harness ... for which I paid ... $50 ... plus $15 shipping ...
All the plastic orifices are the same size: 3/32" ID
Using unexceptional lung power, I pulled and pushed air manually and individually, through each CHECK VALVE.
The larger of the two CHECK VALVES either contains (more likely), or is (less likely), the filtration media; based on the greater difficulty in pulling and pushing air through it (that, and I can't see through it either.
I could neither pull nor push air through either of the two CHECK VALVES 'from blue to white'. BOTH CHECK VALVES only permitted air to pass 'from white to blue'.
The filter on 'shoebox's V&V Harness is only solid blue, not twotone white & blue. Maybe his was merely a filter/flow reducer, but on mine, it's one of two CHECK VALVES.
That neither explains nor justifies the egregiously brazen and ridiculous markups.
(I've heard of Lexus charging $800 for a CMOS battery, by the way, so I'm not surprised, just angry
Though I'll admit that it doesn't answer the question of how much flow needs to be restricted ... how many combo CHECK VALVE/filter/flow reducers of that specific physical configuration could there really be?
3) Since it's apart ... with what, and how, do I test the check valve/filter/flow reducer's restrictive value?