What Is a Safety Valve?

Safety valve is a special valve that is normally closed under the action of external force. When the medium pressure in the equipment or pipeline rises above the specified value, it is a special valve that prevents the medium or pressure in the pipeline or equipment from exceeding the specified value by discharging the medium outside the system . Safety valves belong to the category of automatic valves, which are mainly used on boilers, pressure vessels and pipelines. The control pressure does not exceed the specified value, which plays an important role in protecting personal safety and equipment operation. Note The safety valve must be pressure tested before it can be used.

Chinese name: Safety valve
Category: Automatic valve

Application: Boilers, pressure vessels and pipes
Function: The control pressure does not exceed the specified value,

Development status of safety valves

The safety valve is a special branch of the valve family.

Safety valve In order to be different from other valves that only act as a switch, it is more important to protect the safety of the equipment. With the rapid development of China's economic construction, more and more equipment projects are under pressure control. In view of the need for equipment pressure relief, safety valves play a vital role in protecting the equipment. As of 2013, there have been more than 700 manufacturers and traders of various types of safety valves, with more than 200 inquiries per day, and the supply and demand market for safety valves has significantly increased. According to the preliminary analysis of the first quarter data, the demand for safety valves should be 20 percentage points higher. Safety valves are important safety accessories on boilers, pressure vessels and other pressured equipment. Safety valve (also known as pressure relief valve) is automatically opened and closed according to the working pressure (working temperature) of the pressure system. Generally, it is installed on the equipment or pipeline of the closed system to protect the safety of the system. When the pressure or temperature in the equipment or pipeline exceeds the pressure set by the safety valve, the pressure is automatically opened to release or reduce the temperature to ensure that the pressure (temperature) of the medium in the equipment and pipeline is below the set pressure (temperature) to protect the equipment and pipeline to work normally. Prevent accidents and reduce losses. Safety valves are widely used in: steam boilers, liquefied petroleum

Sealed all copper safety valve Oil and gas automobile tank trucks or LPG railway tankers, oil wells, high pressure bypasses, pressure pipes, pressure vessels, etc. of steam power generation equipment. Safety valves are generally divided into spring-type safety valves, lever-type safety valves, and pulse-type safety valves according to their structural forms. Among them, spring-type safety valves are most commonly used; they are divided into thread-type safety valves and flange-type safety valves according to the connection method. The diameter of the safety valve is generally not large, commonly used between DN15mm-DN80mm, more than 150mm is generally called a large-caliber safety valve. It is an indisputable fact that the market size of the safety valve industry expanded in 2013. There are not many enterprises in China that are qualified to produce safety valves, because safety valves belong to the special equipment industry. The State Administration of Quality Supervision, Administration of Quality Supervision, is more stringent in applying for qualification examinations, and the huge demand for safety valves has undoubtedly given these qualified production safety Valve companies bring more wealth opportunities.

Main role of safety valve

The safety valve plays a safety role in the system. When the system pressure exceeds the specified value, the safety valve is opened, and a part of the gas / fluid in the system is discharged to the atmosphere / pipeline, so that the system pressure does not exceed the allowable value, thereby ensuring that the system does not cause an accident due to excessive pressure.

Technical term for safety valve

Safety valve Nominal pressure: indicates the maximum allowable pressure of the safety valve at normal temperature. The safety valve for high temperature equipment should not consider the reduction of the allowable stress of the material at high temperature. The safety valve is designed and manufactured according to the nominal pressure standard.

Opening pressure: also known as rated pressure or set pressure, refers to the inlet pressure of the safety valve disc when it starts to rise under operating conditions. Under this pressure, there is a measurable opening height. The medium is visually or audibly perceived. Continuous discharge status.

Discharge pressure: the inlet pressure when the valve flap reaches the specified opening height. The upper limit of the discharge pressure is subject to the requirements of relevant national standards or codes.

Overpressure: The difference between the discharge pressure and the opening pressure, usually expressed as a percentage of the opening pressure.

Seat pressure: The valve disc comes into contact with the valve seat again after discharge, that is, the inlet pressure when the opening height becomes zero.

Opening and closing pressure difference: The difference between the opening pressure and the recoil pressure, which is usually expressed as a percentage of the recoil pressure and the recoil pressure. Only when the opening pressure is very low, the pressure difference between the two is used.

Back pressure: the pressure at the outlet of the safety valve.

Rated discharge pressure: The upper limit of the discharge pressure is specified by the standard.

Seal test pressure: The inlet pressure at which the seal test is performed, under which the leakage rate through the sealing surface of the closure is measured.

Opening height: The actual lift of the flap from the closed position.

Flow channel area: refers to the minimum cross-sectional area of the flow channel from the inlet end of the valve disc to the sealing surface of the closing member, which is used to calculate the theoretical displacement without any resistance.

Channel diameter: Corresponds to the diameter of the channel area.

Curtain area: When the flap is above the valve seat, the area of a cylindrical or conical surface formed between its sealing surfaces.

Discharge area: The minimum cross-sectional area of the fluid channel when the valve is discharged. For full-revelation safety valves, the discharge area is equal to the flow channel area; for micro-opening safety valves, the discharge area is equal to the curtain area.

Theoretical displacement: is the calculated displacement of an ideal nozzle with the cross-sectional area of the flow channel equal to the area of the safety valve flow channel.

Displacement coefficient: The ratio of the actual displacement to the theoretical displacement.

Rated displacement coefficient: Product of displacement coefficient and reduction coefficient (taken as 0.9).

Rated displacement: refers to the part of the actual displacement that is allowed as a reference for the safety valve.

Equivalent calculated displacement: refers to the calculated displacement of the safety valve when the conditions such as pressure, temperature, and properties of the medium are the same as the applicable conditions of the rated displacement.

Frequency jump: The valve disc of the safety valve moves back and forth abnormally quickly, and the valve disc contacts the valve seat during the movement.

Flutter: The safety valve disc moves back and forth quickly and abnormally, and the valve disc does not contact the valve seat during the movement.

Classification of safety valves

Safety valve

There are two main types of safety valve structures: spring type and lever type. The spring type refers to the sealing force of the valve disc and the valve seat by the force of a spring. The lever type is the force of the lever and the weight. With the need of large capacity, there is another type of pulse safety valve, also known as pilot safety valve, which is composed of a main safety valve and an auxiliary valve. When the medium pressure in the pipeline exceeds the specified pressure value, the auxiliary valve is opened first, the medium enters the main safety valve along the conduit, and the main safety valve is opened to reduce the increased medium pressure.

The discharge of the safety valve is determined by the diameter of the valve seat and the opening height of the valve disc. It can also be divided into two types: the opening height of the micro-opening is (1/20) to (1/40) of the inner diameter of the valve seat, and the full opening Yes (1/3) to (1/4).

In addition, depending on the application requirements, there are closed and non-closed. Closed type means that the discharged medium is not leaked, and all are discharged along the prescribed outlet. It is generally used for toxic and corrosive media. Non-closed is generally used for non-toxic or non-corrosive media.

Safety valve according to structure

Safety valve structure diagram According to its overall structure and loading mechanism, it can be divided into three types: heavy hammer lever type, spring type and pulse type.

1.Hammer lever safety valve

The heavy-lever lever-type safety valve uses a heavy hammer and a lever to balance the forces acting on the valve disc. According to the principle of leverage, it can use a heavy weight to obtain a larger force through the increase of the lever, and adjust the opening pressure of the safety valve by moving the position of the weight (or changing the weight of the weight).

The heavy-lever lever-type safety valve has a simple structure, is easy to adjust, and is relatively accurate. The added load will not increase significantly due to the rise of the valve flap. It is suitable for high temperature applications. It was used in the past, especially It is used in boilers and higher pressure vessels. However, the weight of the heavy-lever safety valve is heavy, the loading mechanism is easy to vibrate, and it often leaks due to vibration; its seating pressure is low, and it is not easy to close and maintain tightness after opening.

2.Spring micro-opening safety valve

The spring micro-opening safety valve uses the force of a compression spring to balance the force acting on the valve disc. The amount of compression of the spiral coil spring can be adjusted by turning it

Spring micro-opening safety valve The upper adjusting nut is used for adjustment. With this structure, the opening (setting) pressure of the safety valve can be corrected as required. The spring micro-opening safety valve has a light and compact structure, high sensitivity, unlimited installation positions, and low sensitivity to vibration, so it can be used on mobile pressure vessels. The disadvantage of this type of safety valve is that the applied load will change with the opening of the valve, that is, with the rise of the valve disc, the compression of the spring increases, and the force on the valve disc also increases. This is detrimental to the rapid opening of the safety valve. In addition, the spring on the valve will reduce the spring force due to the long-term impact of high temperature. When used on a container with a higher temperature, the heat insulation or heat dissipation of the spring must be considered, which complicates the structure.

3.Pulse type safety valve

The pulse type safety valve is composed of a main valve and an auxiliary valve. The main valve action is driven by the pulse action of the auxiliary valve, and its structure is complicated. Generally, it is only suitable for boilers and pressure vessels with large safety relief.

Among the above three types of safety valves, spring-type safety valves are more commonly used.

Safety valve is divided by medium

According to different media discharge methods, safety valves can be divided into three types: fully enclosed, semi-closed and open.

1.Fully closed safety valve

When the fully enclosed safety valve is exhausted, all the gas is discharged through the exhaust pipe, and the medium cannot leak outside. It is mainly used for the toxic medium. Container for flammable gas.

2.Semi-closed safety valve

Part of the gas discharged from the semi-closed safety valve passes through the exhaust pipe, and part of the gas leaks from the gap between the valve cover and the valve stem. It is mostly used for the container whose medium is a gas that will not pollute the environment.

3.Open safety valve

The bonnet of the open safety valve is open, so that the spring chamber communicates with the atmosphere, which is beneficial to reducing the temperature of the spring. It is mainly suitable for containers whose medium is steam and high-temperature gas that does not pollute the atmosphere.

The safety valve is opened by the disc

According to the ratio of the maximum opening height of the valve flap to the diameter of the safety valve flow channel, the safety valve can be divided into two types: spring micro-open closed high-pressure safety valve and spring full-open safety valve.

1.Spring micro-open closed high pressure safety valve

The opening height of the micro-opening safety valve is less than 1/4 of the diameter of the flow channel, usually 1/40 to 1/20 of the diameter of the flow channel. The action process of the micro-opening safety valve is proportional, which is mainly used for liquid occasions, and sometimes also for gas occasions with small discharge.

2.Spring full-open safety valve

The opening height of the full-open safety valve is greater than or equal to 1/4 of the diameter of the flow channel. The discharge area of a full-open safety valve is the smallest cross-sectional area of the seat throat. Its action process is a two-stage action type, which can only be fully opened with the help of a lifting mechanism. The full-open safety valve is mainly used in the case of gaseous media.

3.Zhongkai safety valve

The opening height is between the slightly open type and the full open type. It can be made into two-stage action or proportional action.

Safety valve is divided according to the principle of action

According to the principle of action, it can be divided into direct-acting safety valves and non-direct-acting safety valves.

1.Direct-acting safety valve

The direct-acting safety valve is opened under the direct action of the working medium, that is, the pressure of the working medium is used to overcome the loading mechanism added to the valve disc.

Safety valve (13 photos)

The mechanical load caused the valve to open. This safety valve has the advantages of simple structure, fast action and good reliability. But because of structural loading, its load is limited and cannot be used in high-pressure, large-caliber applications.

2. Non-direct acting safety valve

This type of safety valve can be divided into pilot-operated safety valve, safety valve with power assist device.

The pilot-operated safety valve is driven or controlled by the medium discharged from the pilot valve. The pilot valve itself is a direct-acting safety valve, and sometimes other types of valves are also used. The pilot-operated safety valve is suitable for high pressure and large diameter applications. The main valve of the pilot-operated safety valve can also be designed to rely on the working medium to seal, or it can apply a much larger mechanical load to the valve disc than the direct-acting safety valve, so it has good sealing performance. At the same time, its movements are rarely affected by back pressure. The disadvantage of this type of safety valve is that its reliability is related to the main valve and the pilot valve. The action is not as fast and reliable as the direct-acting safety valve, and the structure is more complicated.

The safety valve with power assist device is a power assist device that forces the safety valve to open when the pressure is lower than the normal opening pressure. This safety valve is suitable for situations where the opening pressure is very close to the working pressure, or where the safety valve needs to be opened regularly for inspection or to blow off sticky, frozen media. At the same time, it also provides a means of forcibly opening the safety valve in an emergency.

Pressure regulating points of safety valve

Classification according to whether pressure can be adjusted, can be divided into fixed non-adjustable safety valve and adjustable safety valve

1. The pressure value of the fixed non-adjustable safety valve has been set at the factory and cannot be changed during use.

Safety valve It is commonly used in central air-conditioning and air-conditioning, boiler wall-hung boilers, solar energy and other systems, such as S10 series safety valves.

2. The take-off pressure of the adjustable safety valve can be arbitrarily set within a certain range according to the different needs of the user. It is often used in situations where the system protection pressure needs to change frequently, such as the S10 series safety valve, but the price is generally relatively high.

Safety valve according to operating temperature

1. Normal temperature safety valves are generally 110 safety valves, such as 0480 safety valves, which are only installed on HVAC, air conditioning or water systems.

2. High-temperature safety valve refers to a safety valve with a temperature resistance of 180 , such as the 1831 series safety valve, which is specially used in solar systems and mold temperature machine systems.

Safety valve operation method

Adjustment of opening pressure:

Before leaving the factory, the opening pressure of the safety valve should be adjusted one by one to the setting value required by the user. If the user proposes the spring working pressure level, it should be adjusted according to the lower limit of the pressure level.

Before installing the safety valve on the protected equipment or before installation, the user must readjust it at the installation site to ensure that the set pressure value of the safety valve meets the requirements.

Within the range of spring working pressure level indicated on the nameplate, you can adjust the opening pressure by rotating the adjustment screw to change the spring compression.

Before rotating the adjusting screw, the valve inlet pressure should be reduced to less than 90% of the opening pressure to prevent the valve flap from being rotated when the adjusting screw is rotated, thereby damaging the sealing surface.

In order to ensure that the opening pressure value is accurate, the media conditions, such as media type and temperature, should be as close to the actual operating conditions as possible during adjustment. The type of medium changes, especially when the medium accumulation state is different (for example, from liquid phase to gas phase), and the opening pressure often changes. When the operating temperature increases, the opening pressure generally decreases. Therefore, when adjusted at normal temperature and used for high temperature, the set pressure value at normal temperature should be slightly higher than the required opening pressure value. How high is related to the choice of valve structure and material should be based on the manufacturer's instructions.

The conventional safety valve is used to fix the additional back pressure. When the opening pressure is adjusted after the inspection (the back pressure is atmospheric pressure at this time), the setting value should be the required opening pressure minus the additional back pressure.

Adjustment of discharge and recoil pressure:

To adjust the discharge pressure and return pressure of the valve, it is necessary to perform an action test of the valve to the full opening height. Therefore, it can only be performed on a large-capacity test device or after the safety valve is installed on the protected equipment. The adjustment method varies according to the valve structure.

For the structure with recoil disk and valve seat adjusting ring, the valve seat adjusting ring is used for adjustment. Unscrew the fixing screw of the adjusting ring, and extend a tool such as a thin iron rod from the exposed screw hole, then you can turn the gear teeth on the adjusting ring to make the adjusting ring turn left and right. When the adjustment ring is turned counterclockwise to the left, its position rises, and both the discharge pressure and the seating pressure will decrease. Conversely, when the adjustment ring is rotated clockwise to the right, its position decreases, and both the discharge pressure and the recoil pressure will increase. During each adjustment, the adjustment: the rotation of the ring should not be too large (usually a few teeth can be rotated). After each adjustment, the fixing screw should be screwed on so that its end is located in the groove between the two teeth of the adjusting ring, which can prevent the adjusting ring from rotating without generating radial pressure on the adjusting ring. For safety reasons, the inlet pressure of the safety valve should be appropriately reduced before turning the adjusting ring (generally it should be lower than 90% of the opening pressure) to prevent the valve from opening suddenly during adjustment, which may cause an accident.

For the structure with upper and lower adjusting rings (one adjusting ring on the guide sleeve and the valve seat), the adjustment is more complicated. The valve seat adjusting ring is used to change the size of the passage between the valve disc and the adjusting ring, thereby changing the degree of pressure accumulation in the chamber between the valve disc and the adjusting ring when the valve is initially opened. When the valve seat adjustment ring is raised, the degree of pressure buildup increases, thereby reducing the proportion of the valve's opening phase and reaching a sudden rapid opening quickly. Therefore, raising the seat adjustment ring can reduce the discharge pressure. It should be noted that the seat adjustment ring should not be raised too close to the disc. In that way, the leakage at the sealing surface may cause the valve to open suddenly prematurely, but because the pressure of the medium is not enough to maintain the valve disc in the open position, the valve disc then closes again, so the valve will jump frequently. Seat adjustment: "The ring is mainly used to reduce the proportion of the valve, open the stage and adjust the discharge pressure, but also affect the return pressure.

The upper adjusting ring is used to change the angle of turning of the flowing medium after it is reflected on the underside of the valve flap, thereby changing the magnitude of the fluid force, so as to adjust the recoil pressure. When the upper adjusting ring is raised, the turning angle is reduced, and the fluid force is reduced accordingly, so that the recoil pressure is increased. Conversely, when the upper adjustment ring is lowered, the recoil pressure decreases. Of course, the upper adjustment ring also affects the discharge pressure at the same time that it changes the recoil pressure. That is, raising the upper adjustment ring makes the discharge pressure increase, and lowering the upper adjustment ring makes the discharge pressure decrease, but the impact is not as good The seat pressure is so obvious.

Safety valve lead seal:

After the safety valve is adjusted, it should be sealed to prevent the adjusted condition from being changed casually. When repairing the safety valve, record the position of the adjusting screw and adjusting ring before disassembling the valve, so as to facilitate the adjustment work after the repair. After readjustment, it should be sealed again.

Common failures of safety valves

The valve disc does not return to the seat after discharge: This is mainly caused by the spring bent valve stem, the valve disc installation position is incorrect, or it is stuck. Should be reassembled.

Leakage: Under normal operating pressure of the equipment, leakage between the valve disc and the seat sealing surface exceeds the allowable level. The reasons are: there is dirt between the valve disc and the sealing surface of the valve seat. The valve can be opened several times with a lift wrench to flush away the dirt; the sealing surface is damaged. It should be repaired according to the degree of damage by grinding or grinding after turning; the valve stem is bent, tilted or the lever and fulcrum are deflected, so that the valve core and the valve disc are misaligned. Should be reassembled or replaced; spring elasticity is reduced or lost. Measures such as replacing the spring and readjusting the opening pressure should be taken.

[span] Do not open until the specified pressure: the reason for this is that the fixed pressure is not allowed. The compression of the spring or the position of the weight should be readjusted; the valve disc is stuck to the valve seat. Manually deflate or bleed the safety valve; the lever of the lever-type safety valve is stuck or the weight is moved. The weight should be readjusted and the lever moved freely. [span]

After exhausting, the pressure continues to rise: This is mainly because the selected safety valve has a smaller displacement than the equipment's safe discharge capacity, and a suitable safety valve should be selected again; the center line of the valve stem is incorrect or the spring is rusted, so that the valve flap cannot be opened Height, you should reassemble the valve stem or replace the spring; if the exhaust pipe is not cut enough, you should adopt an exhaust pipe that meets the safety discharge area.

Valve flap frequency or vibration: Mainly due to the high spring stiffness. Instead, use a spring with appropriate stiffness; improper adjustment of the adjustment ring will cause excessive back seat pressure. The position of the adjusting ring should be readjusted; the resistance of the discharge pipe is too large, causing excessive discharge back pressure. The discharge pipe resistance should be reduced.

Less than the specified pressure to open: mainly because the constant pressure is not allowed; the spring aging elasticity decreases. Tighten the adjusting screw or replace the spring properly.

Selection principle of safety valve

1. For steam boiler safety valves, the open full-open spring safety valve 0490 series is generally selected;

2. The safety valve for liquid medium, generally chooses the micro-open spring safety valve 0485 series;

3. Safety valve for air or other gaseous medium, generally use full open spring safety valve;

4. Safety valves for LPG tank cars or LPG railway tankers are generally full-open safety valves.

5. Safety valves for oil well exits are generally pilot-operated safety valves;

6. High pressure bypass safety valve for steam power generation equipment, generally pilot-operated safety valve with dual functions of safety and control is selected.

7. If the safety valve is required to be opened regularly, a safety valve with a lift wrench should be selected. When the medium pressure reaches more than 75% of the opening pressure, the valve disc can be slightly lifted from the valve seat by using a lift wrench to check the flexibility of the safety valve opening;

8. If the temperature of the medium is high, in order to reduce the temperature of the spring chamber, when the temperature of the closed safety valve exceeds 300 ° C and the temperature of the open safety valve exceeds 350 ° C, a safety valve with a radiator should be selected;

9. If the back pressure at the outlet of the safety valve is fluctuating, when the amount of change exceeds 10% of the opening pressure, a bellows safety valve should be used;

10. If the medium is corrosive, a bellows safety valve should be selected to prevent important parts from being ineffective due to medium corrosion.

11. The installation and maintenance of safety valves should pay attention to the following points: construction and installation points 1), installation position, height, and inlet and outlet directions must meet the design requirements. Note that the direction of medium flow should be consistent with the direction of the arrow marked on the valve body. close. 2) The appearance inspection of the valve must be performed before installation. The nameplate of the valve should comply with the current national standard "General Valve Mark" GB 12220. For valves with a working pressure greater than 1.0 MPa and a cut-off function on the main pipe, strength and tight performance tests should be carried out before installation, and only approved after use. In the strength test, the test pressure is 1.5 times the nominal pressure, and the duration is not less than 5min. The valve housing and packing should be qualified without leakage. During the tightness test, the test pressure is 1.1 times the nominal pressure; the duration of the test meets the requirements of GB 50243. 1. All safety valves should be installed vertically.

12. There should be no resistance at the outlet of the safety valve to avoid pressure.

13. The safety valve should be specially tested and checked for tightness before installation.

14. The safety valve in use should be checked regularly.

Safety valve installation

Points for setting the safety valve

Pay attention to the following points when setting the safety valve:

(1) When there are gas and liquid two-phase materials in the container, the safety valve should be installed in the gas phase.

(2) When the safety valve is used to discharge flammable liquid, the outlet of the safety valve should be connected to the accident storage tank. When the released material is high temperature combustible, its receiving container should have corresponding protective facilities.

(3) The general safety valve can be vented on-site. The vent should be higher than the operator by 1 meter (m) and should not face the open flame location, sparking place and high temperature equipment within 15 meters (m). The safety valve vents of indoor equipment and containers should lead out of the roof and be more than 2 meters (m) above the roof.

(4) When there is a shut-off valve at the inlet of the safety valve, the shut-off valve should be normally open and sealed to prevent errors.

Safety valve inlet and outlet pipes

(1) The cross-sectional area of the through-holes of the connecting pipes and fittings between the safety valve and the boiler or pressure vessel shall not be less than the inlet cross-sectional area of the safety valve; if several safety valves share one inlet pipe, the flow cross-sectional area of the inlet pipe Not less than the sum of the sectional area of the inlet of the safety valve.
(2) It is generally not allowed to install a shut-off valve between the safety valve and the drum or header of the boiler, or take out the steam outlet pipe. It is generally not suitable to install a shut-off valve or other outlet pipe between the safety valve and the pressure vessel; for pressure vessels containing extremely high, high, and moderate hazards, flammable, corrosive, viscous or valuable media, use The person in charge of the pressure vessel's technical person in charge of the unit approves and formulates reliable preventive measures before installing a shut-off valve between the safety valve and the pressure vessel. During normal operation of the pressure vessel, the shut-off valve must be kept fully open, sealed or locked. The structure and diameter of the stop valve shall not hinder the safety release of the safety valve.

(3) The spring-loaded safety valve adopting screw connection shall be connected with the short pipe with thread, and the short pipe shall be welded with simplified and header tanks.

(4) The safety valve must be equipped with a discharge pipe. The discharge pipe should avoid twists and turns as much as possible to minimize resistance. The discharge pipe should pass through to a safe place and have a sufficient cross-sectional area to ensure the smooth flow of exhaust gas. For safety valves that can interact with each other to produce a chemical reaction, a drain pipe cannot be shared; when the safety valve is installed on a corrosive, flammable gas-containing equipment, anti-corrosion or fire-proof measures should be taken when discharging; When the valve equipment is a toxic medium and the vapor density of the medium is greater than the air density, the medium and steam discharged from the safety valve must be introduced into a closed system and recovered from the closed system to use in production.

(5) The safety valve discharge pipe should be fixed, so as not to cause excessive additional stress to the safety valve or cause vibration.

(6) The safety valve installed in the open air shall be provided with reliable measures to prevent the water content in the medium in the valve from freezing when the air temperature is lower than 0oC, which will affect the discharge of the safety valve.

(7) When the crystallization temperature of the safety valve medium is higher than the minimum ambient temperature, the safety valve must be equipped with a thermal insulation jacket and installed with thermal purge steam to prevent the medium crystallization from blocking the safety valve and affecting the normal operation performance of the safety valve. The inlet and outlet pipelines of the safety valve must also be designed with steam insulation jackets or additional insulation steam companion pipes to prevent medium crystallization from blocking the pipeline.

Safety valve maintenance

1. The safety valve must have a device to prevent the weight from moving by itself and a guide frame to limit the lever's derailment. The spring-loaded safety valve must have a device to lift the handle and prevent the adjustment screw from being turned casually.

2. It should be installed vertically at the highest position of the pot vendor and header. No outlet pipe and valve for taking steam shall be installed between the safety valve and the drum or header.

3. The cross-sectional area of the connecting pipe between the safety valve and the boiler should not be less than the cross-sectional area of the inlet of the safety valve. If several safety valves are installed on a short pipe directly connected to the drum, the cross-sectional area of the passage of the short pipe should not be less than 1.25 times the exhaust area of all safety valves.

4. For boilers with a rated steam pressure of 3.82MPa or less, the throat diameter of the safety valve should not be less than 25mm; for boilers with a rated steam pressure of more than 3.82MPa, the throat diameter of the safety valve should not be less than 20mm.

5. The safety valve should generally be equipped with an exhaust pipe. The exhaust pipe should pass through to a safe place and have a sufficient cross-sectional area to ensure smooth exhaust steam. The bottom of the exhaust pipe of the safety valve shall be equipped with a drain pipe connected to a safe place. No valve shall be installed on the exhaust pipe or the drain pipe.

6. The safety valve of the pressure vessel is best installed directly on the highest position of the pressure vessel body. The safety valve of the liquefied gas tank must be installed in the gas phase. Generally, a short pipe can be used to connect with the container. The diameter of this safety valve short pipe should not be less than the valve diameter of the safety valve.

7. Generally, no valve should be installed between the safety valve and the container. For containers that are flammable, explosive or viscous, for the convenience of cleaning or replacement of the safety valve, a shut-off valve can be installed. The shut-off valve must be fully operated during normal operation Open and add lead seals to avoid tampering.

8. At least two safety valves shall be installed for boilers with a rated evaporation capacity greater than 0.5t / h; at least one safety valve shall be installed for boilers with a rated evaporation capacity less than or equal to 0.5t / h. Safety valves must be installed at the outlet of the split economizer and at the outlet of the steam superheater.

9. For pressure vessels with flammable, explosive or toxic media, the media discharged from the safety valve must have a safety device and a recovery system. The installation of the lever type safety valve must maintain the vertical position, and the spring safety valve should also be installed vertically to avoid affecting its operation. During installation, attention should also be paid to the fit, the coaxiality of the parts, and the bolts should be uniformly stressed.

10. There should be no resistance at the outlet of the safety valve to avoid back pressure. If a drain pipe is installed, its inner diameter should be larger than the exit diameter of the safety valve. The safety valve exhaust should be protected against freezing. The container and drain pipe should be directly connected to the outdoor safe place or there should be facilities for proper disposal. No drain valve is allowed to be installed in the drain pipe.

11. The newly installed safety valve should be accompanied by a product certificate. Before installation, it should be recalibrated, sealed and issued a safety valve for verification.

12. No valve should be installed between the pressure-bearing equipment and the safety valve. For containers that contain flammable, explosive, toxic or viscous media, shut-off valves can be installed for easy replacement and cleaning. Prevents normal operation of the safety valve. In normal operation, the shut-off valve must be fully opened and sealed.

Safety valves belong to the category of automatic valves, which are mainly used on boilers, pressure vessels and pipelines. The control pressure does not exceed the specified value, which plays an important role in protecting personal safety and equipment operation.

Technical index of safety valve

Nominal diameter: DN 4-25

Nominal pressure: PN 25MPa

Applicable medium: oxygen, nitrogen, argon, air, etc.

Applicable temperature: -40 -+ 80

Body: cast steel / stainless steel

Seat: Copper

Valve top, valve stem: stainless steel

Spring: spring steel

Dimensions

Product number	product code	Nominal diameter ()	Nominal pressure (MPa)	Setting pressure (MPa)	Sealing pressure (MPa)	Weight
A21Y-250C / P	1K10	10	1.6	1.2	1.0	2.7
A21Y-250C / P	1K15	15	0.1	0.072	0.06	2.7
A21Y-250C / P	2K4	4	25	twenty two	20	2.7
A21Y-250C / P	2K6	6	25	twenty two	20	2.8
A21Y-250C / P	3K10	10	6	3.3	3.0	3.05
A21Y-250C / P	3K10M	10	6	4	3.6	3.05
A21Y-250C / P	3K10G	10	2.5	1.27	1.1	3.09
A21Y-250C / P	3K10H	10	4	3.15	2.8	3.03
A21Y-250C / P	3K10I	10	1.0	0.22	0.2	3.05
A21Y-250C / P	4K4	4	25	18	16	2.5
A21Y-250C / P	4K6	6	25	17.6	16	2.68
A21Y-250C / P	5K10	10	2.5	1.76	1.6	2.68
A21Y-250C / P	5K15	15	2.5	1.65	1.6	3.8
A21Y-250C / P	6K4	4	10	7.2	6.4	2.8
A21Y-250C / P	6K6	6	10	7.6	6.4	2.65
A21Y-250C / P	6K6G	6	10	9.2	8.4	2.73
A21Y-250C / P	6K15	15	1.0	0.72	0.6	2.93
A21Y-250C / P	8K4	4	10	8.8	8	0.6
A21Y-250C / P	8K10	10	6.0	4	3.6	3.05
A21Y-250C / P	101K10	10	0.6	0.31	0.28	1.72
A21Y-250C / P	152K10	10	1	0.9	0.8	2.97
A21Y-250C / P	252K10	10	4.0	2.55	2.3	2.88
A21Y-250C / P	002K15	15	1.6	0.27	0.24	3.1
A21Y-250C / P	101K15	15	1.6	0.245	0.22	2.83
A21Y-250C / P	1K20	20	0.1	0.07	0.06	3.4
A21Y-250C / P	8K25	25	6.0	4.4	4	1.8
A21Y-250C / P	001K25	25	1.0	0.125	0.11	6.29
A21Y-250C / P	002K25	25	1.0	0.3	0.27	4.97
A21Y-250C / P	302Ad-h15	15	1.6	0.3-0.8	0.27-0.72	4.6
A21Y-250C / P	302Ad-p32	32	1.6	0.065-0.8	0.035-0.72	5.7
A21Y-250C / P	505Aa10	10	4.0	3.2-4	2.88-3.6	3.2
A21Y-250C / P	915Ab4	4	25	19-22	17.1-19.8	3.1
A21Y-250C / P	915Aa-c6	6	25	16-22	14.4-19.8	2.8

Model meaning

Example: A28X-16T

Meaning of safety valve model

A means safety valve

2 means external thread connection

8 means not closed fully open

X indicates that the seat sealing surface is rubber

16 means nominal pressure 1.6Mpa

T means the material is copper

Connection form code

Connection Type	Code	Connection Type	Code
internal thread	1	Pair	7
External thread	2	Clamp	8
Flange	4	card cover	9
welding	6

Structural Form Code

structure type				Code
spring	Closed	With heat sink	Full open	0
		Slightly open		1
		Full open		2
		With wrench	Full open	4
	Not closed		Double spring micro-opening	3
			Full open	8
			Slightly open	7
		With control mechanism	Full open	6
lever	Single leverage
			Full open	2
			Angular slightly open	5
	Double leverage
	Double leverage		Full open	4
	Pilot			9

Seat sealing surface material

Seat sealing surface material	Code	Seat sealing surface material	Code
Copper alloy	T	Nitriding steel	D
rubber	X	Boronizing steel	P
Nylon plastic	N	Cemented carbide	Y
Alloy steel acid or stainless steel	H	Body processing	W
Tin-based bearing alloy (Babbitt alloy)	B

Note: When the material of the sealing surface of the valve seat and valve is different, use a low hardness material code.

Nominal pressure code

The nominal pressure code is represented by Arabic numerals, and its value is 10 times the nominal pressure value in megapascals (MPa).

When labeling the working temperature and working pressure, the working pressure must be marked with P and the maximum temperature of the medium should be added to the lower right corner of the P character. For example, a valve with a working temperature of 540 ° C and a working pressure of 10MPa is coded as P54100.

Body material code

Body material	Code	Body material	Code
grey cast iron	H	Carbon steel	C
Ductile iron	Q	Chrome molybdenum alloy steel	I
		Chrome nickel titanium steel	P
		Chrome molybdenum vanadium alloy steel	V

Note: This code is omitted for gray cast iron valve body with PN1.6MPa and carbon steel valve body with PN2.5MPa.

Safety valve precautions

Safety valve is an important accessory for safety protection of pressure limiting and pressure relief on special equipment (boiler, pressure vessel, pressure pipeline, etc.). Safety valves are usually installed directly on special equipment. Its design, manufacture, installation, use, and inspection must meet the requirements of special equipment, because its reliability and performance are directly related to equipment and personnel Safe and closely related to energy conservation and environmental protection.

1. Common safety valves are generally as follows:

1. According to the overall structure and loading structure, it can be divided into three types: heavy hammer lever safety valve, spring safety valve and control type.

2. According to the ratio of the flap opening height to the valve flow diameter, it can be divided into micro-opening and full-opening safety valves.

3. According to the way of safety valve gas discharge, it can be divided into three types: fully enclosed, semi-closed and open.

Second, the selection of appropriate safety valves should be considered from the following aspects:

1. The structure form mainly depends on the process conditions of the equipment and the working medium and characteristics. Generally, when the amount of boiler and pressure vessel discharge is not large, spring-type safety valves are usually used, otherwise full-open safety valves are better.

2. If the medium is toxic, flammable and explosive, a closed safety valve should be selected

3. Each safety valve has its own working pressure range, and it should be selected according to actual needs when selecting.

4. The discharge of the selected safety valve must be greater than the discharge of the equipment, so as to ensure that some of the medium is eliminated and the pressure continues to rise.

Installation precautions

1. All safety valves should be installed vertically.

2. There should be no resistance at the safety valve outlet to avoid pressure.

3. The safety valve should be specially tested and checked for tightness before installation.

4. Periodically check the safety valve in use

4. Common faults of safety valve in application:

In the normal use and calibration of the safety valve, various faults may be caused due to improper design, manufacture or use. If these failures are not eliminated in time, it will affect the safety valve's efficacy and service life, and in serious cases will endanger the life of the user.

1. Leakage of safety valve.

Leakage at the sealing surface of the valve disc and the valve seat exceeds the allowable level, the cause and solution:

a. The leakage occurs because there is stolen material between the valve disc and the sealing surface of the valve seat, and the valve can be opened a few times and washed down.

b. Seal surface damage can be repaired by grinding or grinding after turning according to the degree of damage.

c. The valve stem is bent and tilted. Should be reassembled or replaced

2. Do not open to the specified pressure and do not close to the specified pressure. This is caused by the incorrect positioning of the safety valve. You should readjust the compression of the spring or the position of the weight or replace the spring.

3. After the safety valve exhausts, the pressure continues to rise. This is mainly because the discharge of the safety valve does not reach the discharge of the equipment, and a suitable safety valve should be selected.

4. The valve flap jumps or vibrates frequently. This is mainly because the spring stiffness is too large, and a spring with an appropriate stiffness should be used instead.

5. The safety valve does not return to its seat after being discharged. Reasons: The spring is bent, the valve stem and the valve disc are installed in an incorrect position or are blocked. They should be reassembled.

Safety valve operation matters

First, always keep the safety valve clean, prevent valve body springs from being filled or corroded by oil and dirt, and prevent the gas safety valve discharge pipe from being blocked by oil or other foreign bodies; often check whether the lead seal is intact and prevent the lever-type safety valve The heavy hammer is loosened or moved to prevent the adjustment screw of the spring-loaded safety valve from being twisted at will.

2. After cleaning the safety valve, it must be re-commissioned.

3. Light oil type safety valve should be used for cleaning.

Fourth, the initial operation stage after commissioning should carefully observe the operation of the safety valve.

5. When the safety valve is found to be leaking, it should be replaced or repaired in time. It is prohibited to increase the load (such as excessively tightening the adjustment screw of the spring-loaded safety valve or adding heavy objects to the lever of the lever-type safety valve) to eliminate the leakage.

6. Regularly check whether the safety valve in operation is leaking, jamming, and rusting of the spring, etc., and pay attention to observe whether the lock nut of the adjusting screw sleeve and the adjusting ring set screw is loose. If problems are found, appropriate measures should be taken in time .

7. The safety valve installed outdoors should take appropriate protective measures to prevent rain, fog, dust, rust and other dirt from entering the safety valve and the discharge pipeline. When the environment is below zero degrees Celsius, necessary anti-freezing measures should be taken to ensure Reliable valve operation.

8. In addition to complying with this regulation when operating gas safety valves, the relevant provisions of the "Safety Technology Supervision Regulations for Pressure Vessels" and "Safety Technology Supervision Regulations for Safety Valves" (TSG ZF001-2004) shall be followed.

phase

Safety valve related standards

Most countries have their own independent agencies to verify the design and performance of a product range in compliance with relevant regulations and standards. This third-party certified system is very common for any security-related product, and is usually also a requirement of the customer before purchase, or of their insurance company.

Actual certification requirements will vary based on specific regulations and standards. In some cases, re-certification needs to take effect every few years, while in other cases, as long as there are no major design changes, whether to re-certify is uncertain, but once a design change occurs, the certification body needs to be notified for re-certification. .

Certification body

Safety valve certification body Norms and standards

Standards related to safety valves vary widely in countries around the world, and many are part of the relevant codes for boilers or pressure vessels.

Some normative standards only outline performance requirements, deviation ranges and basic structural details, but do not give information on dimensions, throat diameter, etc.

Specific provisions. Others are only related to installation and application. It is also common in many markets to cross-use several safety valve standards.

Safety valve standard specification

Development Trend of Safety Valve

China's valve industry chain is numerous, but not a valve powerhouse. On the whole, China has entered the ranks of the world's valve powers, but from the perspective of product quality, there is still a long gap between China and the valve powers. The industry's low concentration of production, low R & D capabilities of valves supporting high-end products, and low manufacturing technology in the valve industry still exist, and the import and export trade deficit continues to expand.

The next few years will be a period of high-speed shocks in the valve industry. The direct consequence of such high-speed shocks is the expansion of the polarization trend in the valve cabinet brand camp. There are definitely not so many valve companies that can really survive the market. However, this high-speed shock of the valve industry will bring huge opportunities, and the results of the shock will make the market operation more rational.

The localization of high-end valves is unusually bumpy. Project basic parts have become a shortcoming that restricts the development of high-end manufacturing in China. During the 12th Five-Year Plan period, the government will continue to increase the localization of high-end equipment components. Here we select several representative valves mentioned in the "Implementation Plan" for the feasibility analysis of import substitution (such as petroleum, power stations, metallurgy, machinery, electronics, mining, chemical, building materials, power, energy , Sewage treatment, etc.). From the analysis, we can see that the feasibility of import substitution of valves in various sub-sectors is very different. High-end valves need more policy guidance and scientific research support.

The valve industry plays a very important role in the development of the national economy as an important link in preparing the manufacturing industry. As China's domestic valve manufacturing industry still has a certain gap compared with the international advanced level, many key valves with high parameters, high temperature, high pressure and high pounds have always depended on imports. After the "Several Opinions of the Equipment Manufacturing Industry", the relevant state departments have made a series of major deployments in accordance with the national requirements for major equipment localization, and are led by the National Development and Reform Commission. Deployed and formulated valve localization plans for major equipment in related fields, and coordinated with relevant departments many times. Nowadays, valve localization has reached a consensus in the domestic valve industry.

Actively adopt international standards for product design; absorb foreign excellent design structures (including patented technology); product tests and performance inspections are carried out in strict accordance with international standards; absorb foreign advanced production process experience and attach importance to the research and promotion of new materials; clarify imported materials The technical parameters and working conditions of high-parameter valve products are the only way to speed up the localization process, promote the continuous updating of valve products, and fully realize the localization of valves.

With the acceleration of the restructuring of the valve industry, the future industry will be competition between valve product quality and safety and product brands. The products will develop in the direction of high technology, high parameters, strong corrosion resistance, and long life. Only through continuous technological innovation and development New products and technical transformation can gradually improve the technical level of the product, meet the domestic equipment supporting, and fully realize the localization of the valve. China's valve manufacturing industry will present a better development prospect under the huge demand environment.

Safety Valve Books

Safety valve information

Author: Zhou Zhen editor

Publisher: China Standard Press

Publication time: 2003-7-1

Edition: 1

Pages: 247

Word Count: 374000

Printing time: 2005-4-1

format:

Paper: offset paper

Impressions:

ISBN:

Packaging: Paperback

Safety valve introduction

This book systematically introduces the basic knowledge of boiler pressure vessel pressure piping, safety valve related regulations, safety valve design, manufacturing, installation, inspection, calibration, The use of quality management and quality control in each link provides a comprehensive theoretical knowledge and rich practical methods for personnel engaged in the professional management and inspection of safety valves in safety supervision and inspection departments of boilers, pressure vessels, and pressure pipes at all levels.

This book was edited by senior engineer Zhou Zhen, and invited engineering and technical personnel who have a high theoretical level and rich practical experience in the design, manufacture, installation, inspection, calibration, and use of safety valves. In the compilation, the latest national regulations and relevant standards on safety valves for boilers, pressure vessels, pressure pipelines, and anti-overpressure safety devices are adopted. The international safety organizations and the United States, Britain, France, Russia, Japan and other countries have collected safety valve Standard. It can be used by enterprise quality management personnel, engineering technicians and safety valve inspectors, and can also be used as training materials for safety valve inspectors.

Safety valve catalog

Chapter 1 Basic Knowledge of Boiler Pressure Vessel and Pressure Piping

Section 1 Definition of Boiler Pressure Vessel Pressure Pipeline and Working Features

Section 2 Classification Method of Boiler Pressure Vessel Pressure Pipes

Section III Structure of Boiler Pressure Vessel Pressure Pipes

Section 4 Manufacturing Quality of Boiler Pressure Vessel Pressure Pipes

Section 5 Pressure Pipeline

Chapter II Relevant Regulations on Safety Valves

Section 1 "Special Equipment Safety Supervision Regulations" (Summary of Contents)

Section 2 "Steam boiler safety technical supervision regulations" (summary of contents)

Section III "Safety Technology Supervision Regulations for Hot Water Boilers" (Summary of Contents)

Section 4 "Regulations on Safety Supervision of Small and Atmospheric Pressure Hot Water Boilers" (Summary of Contents)

Section 5 "Rules for Periodic Inspection of Boilers" (Summary of Contents)

Section 6 "Supervision Rules for Pressure Vessel Safety Technology" (Summary of Contents)

Section VII "Rules for Inspection of In-use Pressure Vessels" (Summary of Contents)

Section 8 "Cylinder Safety Supervision Regulations" (Summary of Contents)

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