Patent ID: 7213787

Claim:
An aircraft, comprising: a fuselage portion; a wing portion; a fuel tank carried by at least one of the fuselage portion and the wing portion; a first conduit coupled to the fuel tank, the first conduit having a first wall aligned with a flow direction in the first conduit; a second conduit disposed annularly around the first conduit, the second conduit having a second wall aligned with the flow direction; an access channel having an aperture in fluid communication with the first conduit, the access channel being isolated from fluid communication with the second conduit; a valve element in fluid communication with the access channel, the valve element being movable between a first position and a second position, the valve element being positioned to allow a first amount of flow through the access channel when in the first position, the valve element being positioned to allow no flow or a second amount of flow less than the first amount of flow through the access channel when in the second position; and a valve unit carrying the valve element, the valve unit including: a passageway having an opening in fluid communication with the access channel; and wherein the valve element includes a piston positioned in the passageway and movable between the first and second positions, the piston having first and second axially spaced apart heads, each sealably disposed against a wall of the passageway with multiple spaced apart seals, wherein the first and second heads are positioned on opposite sides of a reduced diameter portion of the piston that is not sealably disposed against the wall, wherein the first and second heads are on opposite sides of the opening in the passageway when the piston is in the second position, and wherein the first and second heads are on the same side of the opening in the passageway when the piston is in the first position.