BLACK PRESSURE RELIEF VALVE for BALL LOCK KEG LIDS
The holes at the the bottom (of the lid) of the Pressure Relief Valve is smaller than the hole for lids that use the grey PRVs. This is generally used on older tank lids and non-Cornelius lids.
HERE IS A GENERAL RULE:
If there are SIX gas escape holes around the Pressure Relief Valve neck (on the lid), USE A GRAY P.R. VALVE.
If there is ONE or TWO gas escape holes, USE THIS BLACK P.R. VALVE.