The safety valve is widely used in a steam boiler, LPG tanker, oil well, high-pressure bypass, pressure pipeline, pressure vessel of steam power generation equipment, and etc. The safety valve is closed under the action of external force on the opening& closure parts and when the pressure of the medium in the equipment or pipeline exceeds the specified value, it opens and drains the medium out of the system to protect the safety of the pipeline or equipment.
The safety valve shall be installed upright and as close as possible to the protected equipment or piping. If not installed nearby, the total pressure drop between the pipe and the safety valve inlet should not exceed 3% of the valve’s constant pressure value or 1/3 of the maximum allowable open/closed pressure difference (whichever is the lesser). In engineering practice, the total pressure drop of the pipeline can be reduced by expanding the inlet diameter of the safety valve appropriately, adopting a long radius elbow and reducing the number of the elbow. Besides, what else should be considered?
- The safety valve shall be installed in a place convenient for maintenance and a platform shall be set up for maintenance. The large diameter safety valve should consider the possibility of lifting after the safety valve is disassembled. In engineering practice, the safety valve is often mounted on top of the piping system.
- The safety valve for a liquid pipeline, heat exchanger or pressure vessel, which can be installed horizontally when the pressure increases due to thermal expansion after the valve is closed; The outlet of the safety relief valve shall be free of resistance to avoid backpressure and to prevent the accumulation of solid or liquid materials.
- The inlet pipe of the safety valve shall have a long radius elbow with at least 5% bend. The inlet pipe should avoid u-bend as far as possible, otherwise, the condensable material at the lowest point is connected with the continuous flow drain pipe to the same pressure system, the viscous or solid condensate needs the heat tracing system. In addition, the backpressure of the outlet line shall not exceed the specified value of the relief valve. For example, the backpressure of the ordinary spring safety valve does not exceed 10% of its fixed value.
- The sectional area of the connecting pipe between the safety valve and the boiler pressure vessel shall not be less than that of the safety valve. The whole safety valve is installed on a joint at the same time, the cross-section area of the joint shall not be less than 1.25 times of the safety valve.
- The outlet pipeline of the relief valve discharged into the closed system shall be connected to the top of the relief main pipe according to the medium flow direction of 45°, so as to avoid the condensate in the main pipe flowing into the branch pipe and reduce the backpressure of the relief valve.
- If the outlet of the safety valve is lower than the relief pipe or the discharge pipe, it is necessary to raise the access pipe. In steam service, the safety valve shall be installed so that the condensate does not converge upstream of the disc.
- If a discharge line is to be installed, the inside diameter shall be greater than the outlet diameter of the relief valve. For containers of inflammable or toxic or highly toxic media, the discharge line shall be directly connected to an outdoor or safe place with treatment facilities. No valves shall be installed on the discharge line. In addition, flammable, explosive or toxic media pressure vessels must have safety devices and recovery systems. The outlet of the discharge line shall not be directed towards equipment, platforms, ladders, cables, etc.
When the safety valve cannot be mounted on the container body due to special reasons, it can be considered to be mounted on the outlet pipeline. However, the pipeline between them should avoid sudden bending and the outer diameter should be reduced, so as to avoid increasing the pipeline resistance and causing dirt accumulation and blockage. In addition, a power assist device (actuator) is used to open the safety valve when the pressure is lower than the normal set pressure. As a kind of special equipment, when selecting the safety valve, it is necessary to consider the nature of the medium, the actual working condition, the valve material and connection mode and related parameters.