Lightning protected check-type drain valve

A drain valve assembly for a fuel tank comprising:

• a housing secured to a wall of said tank and disposed internally of said tank;
• an opening in a wall of said housing for the flow of liquid in said tank therethrough;
• a cylinder slidably mounted in said housing and under a force normally tending to position it whereby it overlies and blocks said housing opening;
• and
• a piston slidably mounted in said cylinder, said piston being defined at its end inwardly of said tank by a surface having an area substantially greater than the area of the surface at its outer end and located between said cylinder and said housing to resist said normal force and to overlie and block said housing opening, said piston having a longitudinal passage extending therethrough allowing pressure externally of said tank to act on and against the interior of said cylinder and said greater area piston surface to maintain said cylinder out of the overlying and blocking position, and simultaneously to move said piston to the overlying and blocking position and an overpowering force on the outer end of said piston is required to move it relative to said cylinder so as to maintain said cylinder and said piston out of its position of overlying and blocking said housing opening as aforesaid.