Double bellows valve for preventing undesired valve failure positions

A gas turbine engine comprising

• a combustor including an outer combustor case, an inner combustor case that cooperates with the outer combustor case to define a combustion chamber, and a cooling duct coupled to the outer combustor case, and
• a valve coupled with the outer combustor case, the valve comprising:
• a valve body formed to define an air chamber therein, the valve body formed to define a supply inlet for allowing control air to enter the air chamber, a pilot inlet for allowing pilot air into the air chamber, an upstream flow inlet for allowing working air to enter the air chamber from the combustion chamber, and a downstream flow outlet for selectively allowing the working air to exit the valve body through the downstream flow outlet into the cooling duct,
• a valve stem configured to move between a closed position in which the valve stem engages the valve body to close the downstream flow outlet such that the working air is blocked from flowing out of the air chamber and into the cooling duct and an open position in which the valve stem is spaced apart from the valve body to open the downstream flow outlet and allow the working air to flow through the downstream flow outlet and into the cooling duct, and
• an actuator configured to move selectively the valve stem between the closed position and the open position, the actuator including a first bellows coupled with the valve stem and the valve body to define a working fluid chamber that is in fluid communication with the upstream flow inlet and the downstream flow outlet when the valve stem is in the open position and a second bellows coupled with the valve stem and the valve body to define a supply fluid chamber in fluid communication with the supply inlet, and wherein the valve body, the first bellows, and the second bellows cooperate to define a pilot fluid chamber that is in fluid communication with the pilot inlet.