DIN 901 / 902 Spring Loaded Full Lift Safety Valve Application:

DIN 901 / 902 Spring Loaded Full Lift Safety Valve  is applicable as the pressure protecting device in the equipment or pipelines for steam, air,etc.,  which the working medium is  ≤350ºC.

Safety valves were first used on steam boilers during the industrial revolution. Early boilers without them were prone to accidental Explosion.
Safety valves also evolved to protect equipment such as pressure vessel (fired or not) and heat exchangers. Safety valve term should be limited to compressible fluid application (gas, vapor, steam).

The two general types of protection encountered in industry are thermal protection and flow protection.

 For liquid-packed vessels, thermal relief valves are generally characterized by the relatively small size of the safety valve necessary to provide protection from excess pressure caused by thermal expansion. In this case a small valve is adequate because most liquids are nearly incompressible, and so a relatively small amount of fluid discharged through the relief valve will produce a substantial reduction in pressure. 

DIN Standard Safety Valve Specification

A full lift safety valve is one in which the disc lifts sufficiently, so that the curtain area no longer influences the discharge area. The discharge area, and therefore the capacity of the valve are subsequently determined by the bore area. This occurs when the disc lifts a distance of at least a quarter of the bore diameter. A full lift conventional safety valve is often the best choice for general steam applications.

Full lift safety valve opening height is more than one fourth times of the flow diameter. it has an advantage of discharging greatly .