The safety valve comprising housing (10), valve seat (12) and vent port (14) is located in the bottom of the spring housing (18) via a flange (16) locating on the lipped bottom of the spring housing. A pressure block (30) with sprung retaining tags (32) secures the valve housing inside the spring housing via a second lipped groove inside the spring housing. The pressure block also secures the valve element. The valve element comprises an elastic central pad (24) with a mounting membrane (26) whose outer edge is clamped by the pressure block. The bottom of the adjustable spring presses the valve pad onto the valve seat via a central pressure element (28) which has a central recess to locate a stud (38) under the spring support plate. The valve mounting includes a shaped venting profile which provides a clearing blast to keep the valve seat clean.
