The disclosed valve has a cylindrical, central, fluid conducting core fixed within a housing by a nut located in the housing in engagement with an integral flange of said core at the latter's inner end, an oscillatory valve element having a cylindrical wall, one end sleeve portion of which extends within a cylindrical space between the housing and the core to control fluid movement through the latter, and an opposite end sleeve portion of said cylindrical wall having an extremity formation in engagement with a knob for operating the valve, and said valve element being invertible during assembling or disassembling of the valve, in which inverted condition said extremity formation coacts with said nut to effect the latter's insertion or removal in the assembling or disassembling of the valve.