Piston disc spring safety valve is also called with a load of spring safety valve. This safety valve is based on the general safety valve developed on the spring, the main features are two: First, into the disk-shaped spring, and second, the upper part of the valve stem equipped with a piston, the use of compressed air can push the piston up and down . Safety valve in addition to the degree of compression of the spring to control its pressure from the seat, but also through the compressed air to promote the action of the piston control. This safety valve in the normal operation of the boiler, in addition to the valve seat by the spring will be pressed on the seat, but also by the role of compressed air on the piston pressure will spool the valve does not improve the tightness of the safety valve, Reduce leakage and extend the use of orders. When the boiler pressure rises to the safety valve operating pressure, the compressed air quickly opens the safety valve. When the pressure is reduced, the compressed air can be switched to the upper part of the piston to close the safety valve. As the safety valve can quickly Kai, closed, to avoid or reduce the opening and closing of the sealing surface of the blow level. Piston type disc spring safety valve with Kai, closed sensitive, tightness, the use of long-term orders, etc., in some high-volume boilers have been used.