An in line fluid pressure regulating and pressure relief device having a regulator body with an axial bore therethrough with an inlet chamber conectable to a source of fluid under pressure and an outlet chamber connect able to a device requiring fluid under substantially constant pressure. A fluid pressure regulator located in the regulator body maintains fluid pressure at the outlet chamber at a constant predetermined level. A bleed piston located in the axial bore between the inlet chamber and to the pressure regulating means loses contact with said pressure regulating piston when the pressurized fluid source is removed from the regulator or drops below a certain level relieving substantially all pressure in said exit chamber and any attached device passively rendering the device inoperable.