FIELD: mechanical engineering. ^ SUBSTANCE: invention is designed for use in safety devices of hydraulic systems of machines and mechanisms. Proposed safety valve contains piston with bypass hole. Piston divides inner space into two parts. Piston in made in form of stepped plunger being pointed by smaller diameter step to pressure main line and provided with seat end face formed by differential of plunger steps with smaller and larger diameters by means of which it rests on seat. Seat is formed by corresponding bores of inner space of housing for said stepped plunger. Bypass hole is made on end face of plunger smaller diameter step. End face of plunger larger diameter step is provided with displacement stop. Inner space of housing communicates with pressure main line through two holes located in direction of movement of shutoff member and stepped plunger. Additional seat for shutoff member is formed between bore holes of inner space of housing. Diameter of seat of shutoff member in bypass hole of stepped plunger is equal to 0.75-0.85 of diameter of additional seat in housing bore. ^ EFFECT: improved reliability of safety valve by increasing sealing and eliminating conditions for appearance of self-excited oscillations of shutoff member or movable piston. ^ 3 cl, 3 dwg
