Cover for the dome of movable fuel tank

A fuel tank has a domed top with a filling aperture with a first closure and a pressure release valve. The closure further incorporates a gas pendulum valve (54) with a connector fitting to the tank interior and which is shut by a separate closure. The connector fitting or cap has a holder into which the first closure may be stowed. The cap further has a pressure release valve with a connector to the cap and which is closed and sealed in a first position by a second closure. In a second position the second closure links the connector to the ambient atmosphere, and has a protective function. The closure further has a vacuum valve that opens when the vacuum within the tank falls below a given threshold.