snip
A short 1/2" line with full-port fittings and valves will dump 80 CFM at an
insigificant pressure drop, just a few psi at 175 psi.

Backing up here for a moment, the 20 gal tank holds 33 standard cubic feet
of air at 175 psi. That's less than a single half-second blast. If it's
taking more than a half second to dump the tank thru a 1/2" port, there must
be a restriction somewhere.

You forgot that the tank pressure is dropping (flow proportinal
to pressure)pressure at the port is dropping more rapidly than
the average pressure in the tank, and the very rapid cooling
going on. But it's still fast. Unless you are trying to drive a
spud gun, then it is not near fast enough.


Bob