A fluid expulsion system including a tank having a fluid therein and a piston for expelling the fluid from the tank. The piston is mounted in the tank with a gas generator on the first side of the piston and the fluid on the second side of the piston. Responsive to actuation of the gas generator pressure is built up on the first side of the piston and the piston is displaced against the fluid to force the fluid from the tank. The piston and tank passage of the fluid past the piston because of leakage and extrusion due to the gap created between the piston and tank wall responsive to tank expansion under pressure.