If control air pressure is lost, to which position will the fuel oil control valve always fail?

When control air pressure is lost, the fuel oil control valve is designed to fail in a position that prevents any potential hazards associated with improper fuel oil flow. In this case, the fuel oil control valve will fail to the minimum position. This ensures that there is no over-fueling of the system, effectively maintaining safety by reducing the amount of fuel oil being supplied to the combustion process.

Failing to the minimum position is a safety feature, as it prevents the likelihood of an unintended ramp-up of fuel supply that could lead to an unsafe operating condition or even damage to the engines or related systems. By defaulting to this safe state, the system protects itself from potential risks associated with loss of control air pressure, thus prioritizing operational safety above all else.