It is my understanding there is no "flow" through the piston/stem assembly. The power piston itself operates on vacuum and the power stem is along for the ride - putting and relieving spring pressure on the power valve ball. If this the case, the internal diameter of the power stem are mute regarding flow.
Second, careful making the assumption that one who works in a university science department is a scientist, a janitor might think you were just being an [censored].
Cavebull
