Valve system for a fuel tank , in particular valve system for the controlled and/or guided and/or regulated output or insertion of a fluid, preferably gas or air or air enriched or saturated with hydrocarbon atoms, from or into the fuel tank , a) comprising a housing a1) having a tank connection for connecting the valve system to a fuel tank and a2) having a filter connection for connecting the valve system to an active carbon filter and to a filling tube connection for connecting the valve system to a filling tube of the fuel tank , b) wherein either the tank connection and the filter connection or the tank connection and the filling tube connection are connected or can be connected fluidically to each other via a main ventilation channel , wherein at least one main ventilation valve having a valve element is arranged in the main ventilation channel , said valve element sealing the main ventilation channel in a closed position and releasing it in a release position, c) wherein c1) the tank connection or a main ventilation channel on the tank side and the filter connection or a main ventilation channel on the filter side and/or c2) the tank connection or the main ventilation channel on the tank side and the filling tube connection or a main ventilation channel on the filling side, c3) are connected or can be connected fluidically to each other via an ancillary ventilation channel , d) wherein, in the ancillary ventilation channel , at least one valve group is arranged with at least one ancillary ventilation valve , which closes or releases the ancillary ventilation channel . a) comprising a housing a1) having a tank connection for connecting the valve system to a fuel tank and a2) having a filter connection for connecting the valve system to an active carbon filter and to a filling tube connection for connecting the valve system to a filling tube of the fuel tank , a1) having a tank connection for connecting the valve system to a fuel tank and a2) having a filter connection for connecting the valve system to an active carbon filter and to a filling tube connection for connecting the valve system to a filling tube of the fuel tank , b) wherein either the tank connection and the filter connection or the tank connection and the filling tube connection are connected or can be connected fluidically to each other via a main ventilation channel , wherein at least one main ventilation valve having a valve element is arranged in the main ventilation channel , said valve element sealing the main ventilation channel in a closed position and releasing it in a release position, c) wherein c1) the tank connection or a main ventilation channel on the tank side and the filter connection or a main ventilation channel on the filter side and/or c2) the tank connection or the main ventilation channel on the tank side and the filling tube connection or a main ventilation channel on the filling side, c3) are connected or can be connected fluidically to each other via an ancillary ventilation channel , c1) the tank connection or a main ventilation channel on the tank side and the filter connection or a main ventilation channel on the filter side and/or c2) the tank connection or the main ventilation channel on the tank side and the filling tube connection or a main ventilation channel on the filling side, c3) are connected or can be connected fluidically to each other via an ancillary ventilation channel , d) wherein, in the ancillary ventilation channel , at least one valve group is arranged with at least one ancillary ventilation valve , which closes or releases the ancillary ventilation channel . <EOS>