Safety valve is a special branch of valve family. Its particularity is that safety valve only plays the role of opening and closing, and more importantly, it plays a role in protecting the safety of equipment.

The safety valve is normally closed under the external force of the opening and closing parts. When the medium pressure in the equipment or pipeline rises beyond the specified value, it is a special valve that discharges the medium outside the system to prevent the medium pressure in the pipeline or equipment from exceeding the specified value.

Safety valve belongs to automatic valve category, which is mainly used in boiler, pressure vessel and pipeline. The control pressure does not exceed the specified value, which plays an important role in protecting personal safety and equipment operation. The safety valve can only be used after pressure test.

With the rapid development of China's economic construction, there are more and more equipment projects with pressure control. In view of the need of equipment pressure relief, safety valve plays an important role in the process of equipment protection. As of 2013, there are more than 700 manufacturers and traders of various safety valves, with more than 200 daily transaction inquiries. The supply and demand market of safety valves has increased significantly.

Safety valve is widely used in: steam boiler, liquefied petroleum gas tank car or liquefied petroleum gas railway tank car, oil production well, high pressure bypass of steam power generation equipment, pressure pipeline, pressure vessel, etc.

Type of safety valve

Generally, the diameter of safety valve is not large, and the commonly used ones are between dn15mm and dn80mm, and those over 150 mm are generally called large diameter safety valves. Safety valve is divided into full open safety valve and micro open safety valve. According to the overall structure and loading mode of safety valve, it can be divided into four types: static weight type, lever type, spring type and pilot type. It can be divided into screw safety valve and flange safety valve according to different connection ways with pipeline.

Installation method

As a part of the whole equipment system debugging, when the safety valve is opened for the first time, the valve seat is often damaged, because there are always dirt and debris in the system. In order to ensure that foreign impurities do not enter the safety valve, the whole system should be fully flushed before the installation of the safety valve, and the safety valve should be installed in a place where dirt, rust and debris will not gather.

In steam application, it is also very important to reduce the leakage trend through the installation of safety valve. The installation of safety valve shall prevent condensate from gathering at the upstream of valve disc.

Precautions during installation

(1) The newly installed safety valve shall be attached with product qualification certificate. Before installation, it shall be recalibrated, lead sealed and safety valve calibration shall be issued.

(2) The safety valve shall be installed vertically on the gas-phase interface of the vessel or pipeline.

(3) The outlet of the safety valve shall be free of resistance to avoid back pressure. If a discharge pipe is installed, its inner diameter shall be larger than the outlet diameter of the safety valve. Attention shall be paid to antifreeze at the discharge port of the safety valve. For containers containing inflammable, toxic and highly toxic media, the discharge pipe shall be directly connected to the outdoor safe place or have facilities for proper treatment. No valve is allowed to be installed in the discharge pipe.

(4) No valve shall be installed between pressure equipment and safety valve. For containers containing inflammable, explosive, toxic or viscous media, in order to facilitate replacement and cleaning, stop valve can be installed. Its structure and size shall not hinder the normal operation of safety valve. In normal operation, the stop valve must be fully opened and sealed with lead.

(5) For the pressure vessel with inflammable, explosive or toxic medium, the medium discharged by the safety valve must have safety device and recovery system. The installation of the lever type safety valve must be kept in a vertical position, and the spring safety valve should also be installed vertically to avoid affecting its action. During installation, attention shall also be paid to fit, coaxiality of parts and uniform stress of each bolt. The cross-sectional area of the short connecting pipe between the safety valve and the boiler pressure vessel shall not be less than the flow cross-sectional area of the safety valve. The whole safety valve shall be on the same connecting pipe, and the cross-sectional area of the connecting pipe shall not be less than 1.25 times of the total flow cross-sectional area of the safety valve.