Try turning off the gas at the tank but let the burners burn till they go out.  Then turn off the burners.  Then turn on the tank then turn on one the burner and light it and see if this fixes the low gas rate issue.  I had something like this happen on my Bar B Q grill at home it happened when I replaced the tank and when I went to light the grill it was like there was no gas flow.  I did something like I prescribed above and it "fixed" it.
Give it a shot.
Brady

----- Original Message ----
From: Jim Felder <jim.felder@GMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Sent: Friday, July 24, 2009 2:38:56 PM
Subject: How long to get propane purged from scratch?

I blew out an outlet valve a few weeks back and got a new one from
Frank Condelli. I got it installed this morning. Everything is checked
for leaks and OK. Trouble is, I can barely get my burners lit and
they're showing the feeblest flame even wide open after burning for 20
minutes. Is my regulator gone too, and is there anything I can do
about it? I've got to be gone in if for a week starting tuesday.

If it takes a lot longer than that, fine, I'll let it continue to
burn. But if I'm going to get something overnighted for monday
install, I'd better get cranking.

Thanks,

Jim