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 (16, 17) is arranged with at least one ancillary ventilation valve (18, 19), 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 (16, 17) is arranged with at least one ancillary ventilation valve (18, 19), which closes or releases the ancillary ventilation channel.