Had the keg vendor send me some more pressure relief valves, 4 of them, and they all leak. He sweared he pressure tested them all to about 40 psi and they all held. Wonder what the problem is? I managed to wrap one of them in teflon tape and it seems to be holding around 14 psi, but it still doesn't sit well with me. Terrified I'll go to the keg and the CO2 tank will be drained. Anybody got any other ideas???