Balance Pressure Safety Valve Types
A pressure safety valve is designed to open during an emergency or abnormal conditions to prevent a rise of internal fluid pressure in an industrial tank or other piece of equipment. Conventional ones use an internal spring that is overcome by system pressure and allows the fluid to relieve into an open pipe. A balanced valve is a spring-loaded device that incorporates a means for minimizing the effect of back pressure on the relieving discharge pipe.
Other People Are Reading
-
Balanced Safety Valve
-
A balanced safety valve contains a metal bellows directly above the seat disc. This is a series of continuous corrugation that increases the surface area of the top of the disc. If there is back pressure in the discharge pipe, conventional safety valve springs must overcome this added pressure before it can relieve the fluid in the tank. The metal bellows increases the surface area of the force acting down on the disc, which decreases the pressure (pressure is force divided by surface area). A balanced bellows safety valve can overcome back pressures of up to 40 percent of the pressure safety valve setting.
Nonflowing Pilot Operated Valve
-
For pilot-operated valves, the force holding the seat disc in place is the actual system pressure, and not an internal spring. This feature allows a pressure safety valve to be set very close to the system pressure. A nonflowing valve has the process fluid flowing through the pilot valve and into the atmosphere. This is recommended when the process fluid is nonhazardous.
-
Flowing Pilot Operated Valve
-
The flowing pilot-operated safety valve is a type of balanced valve, and is similar to the nonflowing pilot. The process fluid flows through the pilot and into the discharge pipe. Flowing pilot valves are recommended when toxic or flammable materials are in the system that would be hazardous if released into the atmosphere. The use of backflow preventers is also recommended to prevent discharge gases from entering into the flowing pilot lines. Both pilot operated safety valves can utilize remote sensing to avoid inlet pipe pressure drop issues.
-
References
- Photo Credit bronze valve image by YURY MARYUNIN from Fotolia.com
