Originally Posted by
Spider-TW
I like a flow area equivalent to at least a 1/8" diameter hole for RTs. I'll try smaller ports if I like the ASA. If it becomes suspect, I either drill the port out or change the ASA over to a more efficient marker. The other thing that sometimes happens is that the port is across from the flat face of the bottle reg, which sits very close to the bottom of the ASA. Depending on the cut of the bottle reg face and the ASA port, some arrangements can be heavily blocked. Iirc, the CPs have slots in the brass insert near the center.
The old quarter turn SP ASAs had some tiny ports on them.