A flow direction restriction valve mechanism unit includes a pressure decreasing valve assembly that is located to be freely advance or retract in a combination valve cassette attached to an in-outlet secondary side flow path formed on the side of an outlet with respect to an intermediate transmission member in a flow path, and retracts by a pressure of gas; a first coil spring urging the pressure decreasing valve assembly in a retracting direction; a check valve that is located to be freely advance or retract with respect to the pressure decreasing valve assembly, and retracts by a pressure of the gas; and a second coil spring urging the check valve in an advancing direction. A gas induction passage H is formed in which the gas flows and acts on the pressure decreasing valve assembly such that the pressure decreasing valve assembly moves in the advancing direction.

Relevant specifications in the field of gas supply provide for different safety devices for installation in a gas-supply system, in particular, an acetylene-supply system. To provide such a safety device, which is characterized by a compact structure and a high level of operational reliability, this invention proposes that a valve body (1) incorporates an over-pressure valve (4; 104) of a quick-action shut-off device, a control valve (3; 103) of a pressure-limiting device, and a safety valve (2; 102), whereby the safety valve (2; 102) can be fluidically connected to the over-pressure valve (4; 104) and the control valve (3; 103), and closes either when the over-pressure valve (4; 104) opens due to an inlet pressure that is above the inlet-pressure limit value or when the control valve (3; 103) opens due to an outlet pressure that is above an outlet-pressure limit value.