1875 17 Aug. J is a safety or over-pressure valve.
1983 (Nexis) 32 64 The Pro Line BC Jacket has self-adjusting side panels,..overpressure valve with dump, D-rings, quick release buckle on waist and chest, and expandable pockets.
2002 (Nexis) 67 44 Overpressure valves used with buoyancy control system could stick in open position and cause diver to drown.