Abstract: A shut-off valve assembly for refrigerant liquid and/or gases including a valve body (1) having an inlet port, an outlet port and a flat annular valve seat, and a bonnet (2) fitted on the valve body (1). The bonnet (2) is provided with an axially shiftable externally threaded valve stem (3). A mechanism (20) to move the valve stem (3) is rigidly fixed on the valve stem (3). A valve disk (4) is provided with a circular collar. An annular groove is provided adjacent to the circular collar to house a resiliently compressible deformable circular ring (5). The circular ring (5) is placed in the annular groove on the valve disc between the valve disc and seat ring. The circular ring operates to effect a seal in the fluid flow path without requiring maximum compression of the sealing ring between the sealing ring and the valve disc.