tailieunhanh - ARNOLD, K. (1999). Design of Gas-Handling Systems and Facilities (2nd ed.) Episode 2 Part 6

Tham khảo tài liệu 'arnold, k. (1999). design of gas-handling systems and facilities (2nd ed.) episode 2 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Pressure Relief 361 Figure 13-2. Conventional safety-relief valve. Courtesy of API. al relief valves can be used anywhere that back-pressure in the relief header is low. They are common onshore where relief valves are fitted with individual tail pipes. On offshore platforms they are used mainly as small threaded valves for fire and thermal relief and for liquid relief around pumps. In a conventional relief valve a spring holds a disk closed against the vessel pressure. A bonnet covers the spring and is vented to the valve outlet. The outlet pressure p2 acts on both sides of the disk balancing the pressure across the disk except for the portion of the disk open to the vessel pressure Pp The net opening force is equal to P times the area over which P acts. The closing force is the spring force Fs plus p2 362 Design of Gas-Handling Systems and F acilities NON-VENTED BONNET BACK-PRESSURE INCREASES SET PRESSURE Figure 13-3. Operation of conventional safety-relief valve. Reprinted with permission from API RP times the same area where P acts. When the open area times the difference in pressures minus p2 equals the spring force the valve begins to open. Increasing the pressure on the back of the disk p2 or the backpressure will hold the valve closed. Back-pressure is the pressure that builds up in the relief piping and at the outlet of the relief valve. It consists of constant back-pressure in the system back-pressure due to other relief valves relieving and self-imposed back-pressure due to the valve itself relieving. If P2 increases because the valve is installed in a header system with other valves then the amount of pressure in the vessel the set point required to overcome the spring force increases. Conventional relief valves should only be used where the discharge is routed independently to atmosphere or if installed in a header system the back-pressure build-up when the device is relieving must be kept below 10 of the set pressure so the set point is not .