An improved resettable safety valve for preventing the escape of gas from a closed gaseous system wherein an inlet line is attached to the inlet chamber of the valve and an outlet line is attached to the outlet chamber of the valve. The valve comprises a housing wherein a piston-like plug with a head at one end and a rod-like body at the other end are contained within the housing. The housing includes an inlet chamber sized such that the plug head is movable laterally within the chamber. The housing includes a main chamber adjacent the inlet chamber and along the same axis as the inlet chamber and an outlet chamber adjacent the main chamber and along the same axis the main chamber sized such that the rod-like end of the plug fills the chamber at one end thereby preventing the flow of gas through the outlet chamber when the rod-like body is within the outlet chamber. The housing includes two stack-like chambers which are perpendicular to the main chamber having a septum adjacent each chamber thus separating the chambers. The stack-like chambers having a first end with an opening in the main chamber and a second open end. A cap normally abuts the second end of the stack-like chambers and is movable with respect to the opening.
