Safety shut-off valve

In a valve for controlling pressurized fluid wherein:

• a valve body has a passage therethrough for the pressurized fluid;
• a valve gate on a valve stem is movable axially to move the valve gate to open and closed positions;
• a control chamber has a cylindrical wall and an outer end wall secured to a rim end face of the cylindrical wall;
• a piston in said chamber is connected to said stem for inward movement to drive the valve gate inward to one of its positions in response to fluid pressure in the control chamber;
• spring means in the control chamber urges the piston outwardly;
• and said piston has an outer circumferential groove to seat resiliently compressible annular sealing means,
• the improvement to facilitate installation and replacement of said annular sealing means, in which:
• the outer end wall of said chamber is removable for access to the piston;
• said piston is slidably mounted on said stem;
• said spring means seats against the piston to urge the piston outwardly relative to the stem;
• and
• nut means in screw threaded engagement with the stem and abutting the piston to oppose axial outward movement of the piston relative to the stem,
• whereby, with said end wall removed, said nut means may be rotatably moved to a threadedly connected loosened position on the stem to permit the spring means to shift the piston axially outward along the stem to expose the outer circumferential groove of the piston outside the control chamber beyond the rim end face of the cylindrical wall for installation of said annular sealing means and whereby after the annular sealing means is installed in the outer circumferential groove of the piston, said nut means may be tightened on the stem to retract the piston along the stem past the rim end face of the cylindrical wall into the control chamber with the annular sealing means initially visible during the retraction of the piston to minimize the possibility of unobserved damage to the annular sealing means and to minimize the possibility of unobserved inclination of the annular sealing means out of its normal plane during the retraction of the piston.