Filling valve (5) including: a hollow housing (11) having a valve seat (25); a moving valve rod (14) slidingly mounted in the housing (11) and having a sealing surface (23), the moving valve rod (14) and the hollow housing (11) together defining a liquid chamber (18); a liquid inlet (26) for putting the liquid chamber (18) into communication with a liquid supply pipe (6); a device for putting the valve rod (14) in a first, full-open position, in which the sealing surface (23) is spaced from the valve seat (25), thereby forming a passage (27) for the liquid; a device for putting the valve rod (14) in a second, closed position, in which the sealing surface (23) is in sealing contact with the valve seat (25), thereby closing the passage (27), and a device for putting the valve rod (14) in a third, predetermined, semi-open position in which the sealing surface (23) is spaced from the valve seat (25) but closer to the same than in the full-open position.