Abstract: A safety valve has a valve body, a piston contained in the valve body, a soluble alloy filled between said piston and said valve body, and a spring inserted between the piston and the valve body. The piston includes a path connecting both ends thereof, and has a first gas pressure receiving surface and a second gas pressure receiving surface at both ends. The first and second gas pressure receiving surfaces have the same area; the piston works as a balanced piston where the gas pressure in the fuel tank functions in reverse directions. As a result, no gas pressure is applied to the soluble alloy but only the energizing force of the spring is applied. Therefore, the pressure applied to the soluble alloy can be kept constant without regard to the increase of the gas pressure.

Abstract: A safety valve has a valve body, a piston contained in the valve body, a soluble alloy filled between said piston and said valve body, and a spring inserted between the piston and the valve body. The piston includes a path connecting both ends thereof, and has a first gas pressure receiving surface and a second gas pressure receiving surface at both ends. The first and second gas pressure receiving surfaces have the same area; the piston works as a balanced piston where the gas pressure in the fuel tank functions in reverse directions. As a result, no gas pressure is applied to the soluble alloy but only the energizing force of the spring is applied. Therefore, the pressure applied to the soluble alloy can be kept constant without regard to the increase of the gas pressure.