Quick exhaust valve from Humphrey, what's the problem?

[psycix]

I mean that with blowing, the velocity is too low to measure to give a good flow comparison.
But when the air comes further near the speed of sound, the effects of blocking flow will increase.

[ozzioutlaw]

hey guys. i was thinking of buying one of these Humphrey qevs for my next project its only a 1/4 will i have any problem with blockage at 200-400psi?? the barrel is going to be slowly reduced to a 4mm barrel the 1/4 qev is around around 6.2 mm i wana reduce it to 4mm for my pellets