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How does the safety valve function
Release Time:2019-04-22      Hit Count:2829

(1) safety valve

When the pressure vessel is running under normal working pressure, the safety valve should be kept tight. When the pressure exceeds the set value, the safety valve will open automatically under the pressure to relieve the pressure of the container to prevent the damage of the container or pipeline; When the pressure of the container is released to the normal value, it can close by itself and stop releasing.

1. Type of relief valve

The safety valve is divided into lever type and spring type according to its overall structure and loading mechanism. Spring safety valves are commonly used in petrochemical plants. The loading device of the spring-type safety valve is a spring. By adjusting the nut, the compression amount of the spring can be changed and the compression force of the disc on the seat can be adjusted to determine the opening pressure. The spring type safety valve is compact in structure, small in volume, sensitive in action, not too sensitive to vibration, and can be installed in a movable container. The disadvantage is that the spring inside the valve is affected by high temperature, the elasticity is reduced.

2. Selection of safety valve

"Code of supervision of safety technology of pressure vessel" regulation, the manufacturing unit of safety valve, the manufacturing license that must have national labor ministry to issue just can be made. The products shall be delivered with a certificate, which shall bear the seal of the quality inspection department and the date of inspection.

The selection of the safety valve should be based on the process conditions of the container and the characteristics of the working medium. The discharge of safety valve is the key factor of selecting safety valve.

From the perspective of gas emission, closed safety valve should be used for medium containers containing toxic, flammable or polluting environment.

When selecting the safety valve, pay attention to its working pressure range and match it with the working pressure range of the pressure vessel.

3. Installation of safety valve

The relief valve shall be installed vertically upward in the gas-phase space above the liquid level of the pressure vessel body or connected with a pipe connected to the gas-phase space of the pressure vessel. The safety valve is indeed not installed on the container body, and when connecting the container with a short pipe, the diameter of the pipe must be greater than the diameter of the safety valve inlet, the valve or other outlet pipe is generally prohibited on the pipe. When several safety valves are installed at one port of the pressure vessel, the area of the interface inlet shall be at least equal to the sum of the area of several safety valves. Between pressure vessel and safety valve, should not be commonly installed between cut-off valve, to dress up for extremely flammable, toxic, highly, highly harm or container of viscous medium, to facilitate the relief valve replacement, cleaning, can stop valve, but stop valve flow area shall not be less than the minimum of the relief valve flow area, and to have reliable measures and strict system, to ensure that cut-off valve in the operation to remain fully open and seal.

When selecting the installation location, the convenience of daily inspection, maintenance and overhaul of the safety valve should be taken into account. Installed in the outdoor outdoor safety valve, there should be a reliable measure to prevent moisture freezing in the winter valve. The minimum cross-sectional area of the relief valve exhaust pipe fitted with the exhaust pipe shall be greater than the cross-sectional area of the outlet of the relief valve, and the exhaust pipe shall be as short and straight as possible without a valve. A lever relief valve must be installed with its stem in a plumb position. All bolts connecting flanges of intake pipe and exhaust pipe must be tightened evenly to avoid additional stress on the valve body, damaging the concentricity of the valve body and affecting the normal operation of the safety valve.

4. Safety valve adjustment, maintenance and inspection

The safety valve shall be tested for water pressure and air tightness by professionals before installation, and adjusted and corrected after passing the test. The opening pressure of the relief valve shall not exceed the design pressure of the container. The adjusted relief valve shall be lead sealed. In order to make the safety valve work sensitively and reliably and seal well, routine maintenance inspection must be strengthened. The relief valve should always be kept clean to prevent the valve spring from being stuck or corroded by oil and dirt. Also should often check the safety valve seal is intact, the temperature is too low, there is no possibility of freezing, check the safety valve whether there is a leak. For lever relief valves, check that the weight is loose or moved, etc. If defects are found, they should be corrected or replaced in time.

Pressure vessel safety technical supervision regulation stipulates that the safety valve should be inspected regularly at least once a year. Regular inspection includes cleaning, grinding, testing and calibration.

(2) explosion-proof sheets

Explosion-proof sheet, also known as explosion-proof film and explosion-proof plate, is a kind of fracture-type safety pressure relief device. The explosion-proof sheet has the advantages of good sealing performance, quick reaction and not easy to be affected by the dirt in the medium. However, the pressure is relieved through the rupture of the diaphragm, so the vessel cannot be used any longer and the vessel is forced to stop operation. Therefore it is only used on pressure vessels not suitable for the installation of safety valves.

The structure of explosion-proof sheet is relatively simple. Its main part is a very thin metal plate, with a pair of special pipe flange clamping into the container out of the short pipe, also have the diaphragm and seal gasket together directly into the flange of the pipe. In normal operation, although the flameproof sheet may be deformed, it can keep tight. When the container overpressure, the diaphragm is broken discharge medium, to avoid the container because of overpressure and explosion.

The designed bursting pressure of the flameproof disc is generally 1 of the working pressure. 25 times, to the pressure fluctuation amplitude big container, its design breaks the pressure to be also corresponding big some. However, under no circumstances shall the bursting pressure of the flameproof disc be greater than the design pressure of the container.

(3) explosion-proof cap

Explosion-proof cap, also known as blasting cap, is also a kind of fracture-type safety pressure relief device. It has many styles, but the basic principles are the same. Its main component is a thick - walled short tube with a closed end and a dry - weak section in the middle. When the pressure of the container exceeds the prescribed limit, the explosion cap will break from the weak section and the gas will be discharged from the pipe hole. In order to prevent explosion cap from flying out and injuring people, protective devices should be installed on the outside of it.

Pressure gauge

Pressure gauge is a kind of metering instrument for measuring medium pressure in pressure vessel. There are many kinds of pressure gauges, including liquid column type, elastic element type, piston type and electric quantity type. Most pressure vessels use single spring tube pressure gauges of elastic element type.

Pressure gauges mounted on pressure vessels shall have dial limits equal to 1 of the highest working pressure of the vessel. 5 to 3 times, preferably 2 times. The larger the range of the pressure gauge, the larger the absolute value of the allowable error and the larger the visual error. Pressure gauges shall be selected according to the pressure level and working requirements of the vessel. According to the pressure class requirements of the container, the pressure of the container is generally not less than 2. Level 5, medium and high pressure vessels should not be less than 1. Level 5. In order for the operator to clearly and accurately see the pressure indicator, the diameter of the pressure dial shall not be too small. In general, the dial diameter should not be less than 1OOmm. If the pressure gauge is far from the observation site, dial diameter increases, when the distance exceeds 2m, dial diameter should not be less than 150mm; When the distance exceeds 5m, do not be less than 250mm. The dial diameter of the pressure gauge for the uhp vessel shall not be less than 150mm.

When installing the pressure gauge, in order to facilitate the operator to observe, the pressure gauge should be installed in the most eye-catching place, and there should be sufficient lighting, at the same time pay attention to avoid the impact of radiation heat, low temperature and vibration. Pressure gauges installed at elevated locations should be tilted slightly forward, but not by more than 300 degrees. The pressure gauge connection shall be directly connected with the vessel body. In order to facilitate the unloading and calibration of the pressure gauge, the pressure gauge and the container should be installed between the three-way cock. The cock shall be mounted on the vertical section of the pipe with an open mark for verification and replacement. Steam vessels shall be provided with a trap between the pressure gauge and the vessel. Containers containing high temperature, strong corrosion and condensing media should be equipped with isolation buffer device between the pressure gauge and the container.

The use of the pressure gauge, should be based on the highest working pressure of the equipment, in its dial marked warning line, but not painted on the dial glass, so as to avoid the glass rotation so that the operator has an illusion, resulting in accidents.

Pressure gauges without qualified inspection and without lead seal are not allowed to be installed and used.

The pressure gauge should be kept clean, the glass on the dial should be bright and transparent, so that the pressure value indicated by the pointer in the gauge can be clearly seen. The connection of the pressure gauge should be blown clean regularly. During the operation of the container, if it is found that the indicator of the pressure gauge is out of order, the scale is not clear, the dial glass is broken, the pointer does not return to zero after the pressure relief, and the lead seal is damaged, etc., it shall be corrected or replaced immediately.

The maintenance and calibration of pressure gauges shall comply with the relevant provisions of the national metrological department. The pressure gauge shall have a calibration mark indicating the date of next calibration or the expiry date of calibration. The pressure gauge after calibration shall be sealed with lead.

(5) liquid level meter

The level gauge is a safety accessory for pressure vessels. The liquid level of the general pressure vessel shows the liquid level of the multi-purpose glass plate gauge. Pressure vessels for petrochemical installations, such as those for the storage of various liquefied petroleum gases, shall be equipped with liquid level indicating instruments of different principles of action, structures and performances. The medium is the pressure vessel of powder material, most of them choose the gauge of radioactive isotope material level to indicate the height of powder material level.

No matter what type of liquid level gauge or instrument is selected, it shall meet the safety requirements of the pressure vessel safety technical supervision regulation, mainly including the following aspects:

1. Should according to the pressure vessel medium, the highest working pressure and temperature to choose correctly.

2. Before installation and use, the liquid level of low and medium pressure vessels shall be measured 1. Water pressure test with nominal pressure of 5 times liquid level gauge; High pressure container level gauge, should carry out 1. Hydraulic test for nominal pressure of 25 times liquid level gauge.

3. Holding 0 ℃ under medium pressure vessels, should choose frost prevention liquid level gauge.

4. For outdoor liquid level meters in cold areas, jacket type or heat preservation type liquid level meters should be selected.

5. Liquid gas pressure vessels with extremely flammable, toxic or highly hazardous media shall use panel or automatic liquid level indicator and shall have protective devices against leakage.

6. If the liquid level indication is required to be stable, float (standard) type liquid level gauge shall not be used.

7. The level gauge shall be installed in an easy-to-observe position. If the mounting position of the level gauge is not easy to observe, additional auxiliary facilities shall be added. Large pressure vessels should also have centralized control facilities and alarm devices. The maximum and minimum safe levels of the level gauge shall be clearly marked.

8. Pressure vessel operators should strengthen the maintenance and management of liquid level, and keep it in good condition and clear. The system of periodic maintenance shall be implemented for the liquid level meter, and the user may specify it in the management system according to the actual operation situation.

9. The liquid level shall be discontinued under any of the following circumstances:

More than the inspection cycle;

(2) glass plate (pipe) crack, broken;

The valve parts fixed;

(4) often appear false liquid level.

10. For the use of radioactive isotope material level measuring instruments, the provisions of the regulations on the protection of radioactive isotopes and radiological devices promulgated by the state council shall be strictly implemented, and effective protective measures shall be taken to prevent on-site radiation hazards.

In addition, in the process of petrochemical production, some reaction pressure vessels and storage pressure vessels are also equipped with liquid level detection alarm, temperature detection alarm, pressure detection alarm and interlock, which are not only production monitoring instruments, but also the safety accessories of pressure vessels. Therefore, management should be strengthened according to the requirements of relevant regulations. These safety accessories are not only used in common boilers, but also widely used in most liquefied gas transport vehicles.


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