- A timed automatic closing mechanism (2; 102) for a tap (1; 101), such as a tap for a shower, washbasin or urinal, which comprises: - a hollow cylindrical housing (12; 112) in which a control rod (7; 107) is axially slidable, the upper end of the control rod (7; 107) being configured to be integral with a tap control knob (6; 106), the lower part of the hollow cylindrical housing (12; 112) constituting an auxiliary seat (19; 119), the lower end of the control rod (7; 107) carrying an auxiliary valve (18; 118) associated with said auxiliary seat (19; 119), the return of the auxiliary valve (18; 118) onto its auxiliary seat (19; 119) being caused by a first compression spring (14; 114), at least one pressure relief channel (34; 134) being provided in the hollow cylindrical housing (12; 112) downstream of the auxiliary seat (19; 119) to allow a fluid flow to a pressure relief outlet (5; 157) when the auxiliary valve (18; 118) is open; - a timing cylindrical chamber (21; 121) whose upper part is fluidly connected to the lower part of the hollow cylindrical housing (12; 112) and in which a timing piston (24; 124) is slidable, which carries a main valve (25; 125) associated with a main seat (26; 126) provided at the bottom of the timing cylindrical chamber (21; 121), said timing cylindrical chamber (21; 121) being configured to be connected to a fluid inlet (4; 104) of the tap (1; 101) via at least one fluid inlet opening (38; 138) provided in the timing cylindrical chamber (21; 121), said main valve (25; 125) being integral with a lip seal whose lip rests on the inner side surface of the timing cylindrical chamber (21; 121), the inner side surface of the timing cylindrical chamber (21; 121) comprising a longitudinal groove (35; 135) to allow a calibrated fluid leakage between the portion of the timing cylindrical chamber (21; 121) above the lip seal and the portion of the timing cylindrical chamber (21; 121) below the lip seal upon movement of the timing piston (24; 124), the return of the main valve (25; 125) to its main seat (26; 126) being caused by a second compression spring (32; 132) and being slowed down by the lip seal in accordance with the cross-sectional area of said longitudinal groove (35; 135); - at least one outlet channel (31; 131) provided downstream of the main seat (26; 126) and allowing a fluid flow to a fluid outlet (5; 105) of the tap (1; 101); and characterized in that it comprises: - a secondary valve (29; 129) carried by the lower end of a plunger (28; 128) integral with the timing piston (24; 124), said plunger (28; 128) penetrating into the main seat (26; 126), a secondary seat associated with said secondary valve (29; 129) being provided between the main seat (26; 126) and the at least one outlet channel (31; 131). - a hollow cylindrical housing (12; 112) in which a control rod (7; 107) is axially slidable, the upper end of the control rod (7; 107) being configured to be integral with a tap control knob (6; 106), the lower part of the hollow cylindrical housing (12; 112) constituting an auxiliary seat (19; 119), the lower end of the control rod (7; 107) carrying an auxiliary valve (18; 118) associated with said auxiliary seat (19; 119), the return of the auxiliary valve (18; 118) onto its auxiliary seat (19; 119) being caused by a first compression spring (14; 114), at least one pressure relief channel (34; 134) being provided in the hollow cylindrical housing (12; 112) downstream of the auxiliary seat (19; 119) to allow a fluid flow to a pressure relief outlet (5; 157) when the auxiliary valve (18; 118) is open; - a timing cylindrical chamber (21; 121) whose upper part is fluidly connected to the lower part of the hollow cylindrical housing (12; 112) and in which a timing piston (24; 124) is slidable, which carries a main valve (25; 125) associated with a main seat (26; 126) provided at the bottom of the timing cylindrical chamber (21; 121), said timing cylindrical chamber (21; 121) being configured to be connected to a fluid inlet (4; 104) of the tap (1; 101) via at least one fluid inlet opening (38; 138) provided in the timing cylindrical chamber (21; 121), said main valve (25; 125) being integral with a lip seal whose lip rests on the inner side surface of the timing cylindrical chamber (21; 121), the inner side surface of the timing cylindrical chamber (21; 121) comprising a longitudinal groove (35; 135) to allow a calibrated fluid leakage between the portion of the timing cylindrical chamber (21; 121) above the lip seal and the portion of the timing cylindrical chamber (21; 121) below the lip seal upon movement of the timing piston (24; 124), the return of the main valve (25; 125) to its main seat (26; 126) being caused by a second compression spring (32; 132) and being slowed down by the lip seal in accordance with the cross-sectional area of said longitudinal groove (35; 135); - at least one outlet channel (31; 131) provided downstream of the main seat (26; 126) and allowing a fluid flow to a fluid outlet (5; 105) of the tap (1; 101); and characterized in that it comprises: - a secondary valve (29; 129) carried by the lower end of a plunger (28; 128) integral with the timing piston (24; 124), said plunger (28; 128) penetrating into the main seat (26; 126), a secondary seat associated with said secondary valve (29; 129) being provided between the main seat (26; 126) and the at least one outlet channel (31; 131).