FIELD: under-layer fire fighting systems; safety valves breakable members for reservoirs with highly inflammable liquids. SUBSTANCE: proposed diaphragm valve has ring-shaped housing with cavity from side of end in which gate is installed for one-side outgoing from cavity under action of working mixture pressure differential acting onto gate from two sides. Burst diaphragm is secured on ring and gate to hermetically isolate working mixtures from each other in initial position. Valve is furnished additionally with knife with inner blade cutting the diaphragm at movement of gate which is made axle-shafts displaced relative to axes of symmetry. Axle-shafts get into mating slots made in housing. Bottom of cavity in ring is made to smaller generatrix of inner part of ring surface from one slot to the other. EFFECT: provision of reliable operation at minimum working mixture pressure differential and opening of maximum area of pipeline passage in operating position, reliable closing of pipeline section at return into initial position. 4 cl, 2 dwg
