Back pressure of the safety valve
Thread Content
1. How is the back pressure of a safety valve determined? 2. Does back pressure affect the calculation of the minimum discharge area? 3. What impact does the back pressure of a safety valve have on it?
1. The pressure to which a safety valve is subjected depends on whether its outlet is directly connected to the atmosphere or to a pipeline; if it’s connected to the atmosphere, then it’s not under any pressure, while if it’s connected to a pipeline, the pressure applied is that of the pipeline itself. 2. Pressure is a factor in the calculation formulas, and it affects the determination of the appropriate diameter for the safety valve. 3. Pressure also influences the selection of safety valves; for more details, refer to API520
1. Back pressure, in simple terms, is the pressure in the exhaust pipe (outlet). 2. Impact. The greater the back pressure, the larger the exhaust port area. 3. If the outlet is blocked, gas cannot be released, and the function of the safety valve is reduced or eliminated.
Back pressure certainly affects the design and selection of safety valves. When the back pressure is high, ordinary spring-loaded safety valves can no longer be used; instead, bellows-type valves are required. If the pressure is even higher, then pilot-operated safety valves are needed.
The calculation of the back pressure for safety valves can refer to API520, API521, or HG20570. The discharge capacity of the safety valve on the backpressure side has a significant impact; the calculation of backpressure must take into account the pressure at the flare inlet (if any), as well as the pressure drop in the discharge piping system.
Determining the back pressure for a safety valve depends on the type of medium discharged by it. For substances like air, which are simply vented to the atmosphere, the back pressure is equal to atmospheric pressure. If it is a combustible gas, it must be discharged into a flare system, and in that case the pressure in that flare system needs to be taken into account. When calculating the minimum discharge area when the back pressure is high, a back pressure correction factor must be considered
http://bbs.hcbbs.com/thread-134941-1-1.html This might be able to help you
1. Valve outlet pressure and back pressure ； 2. Back pressure is an essential parameter in calculating the throat. 3. The greater the back pressure, the greater the resistance that the safety valve must overcome. For valves of the same model, those with higher back pressure have a relatively lower discharge capacity.