HOW SAFETY VALVE WORKS ?

Safety valve

The main purpose of safety valve is protect, environment and life. Which is designed to open and relive the  excess pressure from vessels or pipe lines re close and prevent the further release of fluid after normal conditions have restored.
Safety valve is most device to operate all time and any circumstances safety valve is a not a pressure regulation and control valve which is not applicate for those operations but only used for over pressure protection purpose only

WHY EXCESS PRESSURE DEVELOPED IN VESSELS OR SYSTEM :

There are number of reasons for why excess pressure develops in vessel or any system which have some reasons, that given below :

1) Blocked discharge
2) Exposed to external fire
3) Thermal expansion
4) Chemical reactions
5) Heat exchanger tube rapture
6) Cooling system failure 

For example in steam boiler the safety valve used for over pressure protection for main steam line and steam drums the safety valve will be opens when pressure of boiler increased to over the design pressure in this way which saves the equipment life and environmental protection,

 HOW MANY TYPES OF SAFETY VALVES MAINLY :

Mainly there are two types of safety valves 

 
1) loaded safety valves
2) Pilot loaded safety valves 

Spring loaded safety valves :

Valve closing :

The direct spring loaded safety valves in which closing force or spring force applied by the helical spring which is compressed by adjusting screw spring force is transferred via spindle on to disc.The disc seal against the nozzle as long as spring force is larger then the force created by pressure at the inlet valve.

Valve opening : 

This safety valve open at a predetermined set pressure. The spring force is acting in closing direction, the force created by the pressure at the inlet of the safety valve, is acting in opening direction. At the set pressure the forces are balanced. There is no resulting force to keep the disc down on the seat. This safety valve visibly or audibly start to leak