Characteristics of the safety valve

Characteristics of the safety valve

For a metal-seated valve to provide an acceptable shut-off, the sealing surfaces need to have a high degree of flatness with a very good surface finish. The disc must articulate on the stem and the stem guide must not cause any undue frictional effects. Typical figures required for an acceptable shut-off for a metal seated valve are 0.5 mm for surface finish and two optical light bands for flatness. In addition, for a reasonable service life, the mating and sealing surfaces must have a high wear resistance.

Unlike ordinary isolation valves, the net closing force acting on the disc is relatively small, due to there being only a small difference between the system pressure acting on the disc and the spring force opposing it.

Resilient or elastomer seals incorporated into the valve discs are often used to improve shut-off, where system conditions permit. It should be noted, however, that a soft seal is often more susceptible to damage than a metal seat.