A mechanical valve assembly for the control of a gas flow to a gas appliance. The mechanical valve assembly includes at least one input knob movably connected to a housing, a shaft assembly connected to at least one input knob, and a manually-operated valve located inside the housing and in between the inlet port and the outlet port. The manually-operated valve is mechanically connected to the shaft assembly, and the manually-operated valve is configured for opening and closing a gas flow between the inlet port and the outlet port.