I found this: An 8-inch booster with 20 inches of engine vacuum will provide about 240 lbs. of brake assist.
From that, I would suspect that different vehicles utilizing different size brake boosters or having different size engines would require a valve with different values. If an engine is losing compression, it seems that the efficiency of the braking system would diminish since vacuum is created at the intake manifold.
Input and output ends may be different in order to prevent them from being installed backward. The valve only allows air to be sucked out of the booster. There is a constant vacuum on both sides of the booster diaphragm that 'assists' the efforts in the direction the diaphragm is pushed when the pedal is operated. Valving inside the master cylinder cuts off the vacuum on one side when the pedal is pushed. The diaphragm returns to a relaxed position when the pedal is released. The reason there is vacuum on both sides is to prevent the brakes from being applied all the time. If the valve were turned around, the valve wouldn't open.
Checking Rock Auto for a 93 Beretta which had 3 available engines and the 86 Fiero which had 2 available engines, the part numbers are different between brands of cars, but are the same within the brand car for all engines. Seems if all check valves were of the same value, there would be one universal valve.
