Safety Shut-off Valves
Safety shut-off valves (SSOVs) are the primary automatic means of turning gas flow ON and OFF for furnaces, ovens, and in some cases, individual burners (keep in mind that a "manual shut-off valve" is always required). SSOVs are required by national codes and standards with at least two SSOVs required between a burner and the fuel supply. Besides that, they are a good way of keeping you and your factory from joining the upper atmosphere.
In conjunction with "code-required safety circuits", the SSOVs automatically close in the event of a detected hazardous condition.
SSOVs
- are required to close in less than one second
- have an effective leakage rate of 0 (it's actually a really, really small number)
- include visual indication (a means of showing if they are opened or closed)
- usually include a means of electrically proving closure (either a "proof of closure switch" or a "leak-detection/tightness control" system)
SSOVs can incorporate additional features making them useful for
- reducing system pressure (like the VAD)
- automatically matching gas pressure to an impulse pressure (like the VAG)
- "pulse-firing" applications requiring high duty cycles
