(1) The setting pressure is inaccurate. Countermeasures: Readjust the compression of the spring;

(2) The elasticity of the spring decreases as it ages. Due to long-term use or medium corrosion, the spring ages and its elasticity decreases. Countermeasures: Tighten the adjusting screw appropriately or replace the spring.

(3) The operating temperature increases, resulting in a decrease in opening pressure. Countermeasures: When adjusting at normal temperature and using it at high temperature, the set pressure value at normal temperature should be slightly higher than the required opening pressure value.

(4) Due to leakage and other reasons, the operating environment of the safety valve is higher than the allowable working temperature of the spring, causing the spring elastic force to decrease. Countermeasures: Grind the sealing surface in time to eliminate leakage and replace with a new spring.

(5) The safety valve is tilted. The safety valve is tilted due to installation or contact and extrusion. Countermeasures: Safety valves, especially dead weight safety valves and lever safety valves, must be installed vertically and equipped with a solid protective ring.

(1) The setting pressure is inaccurate and the setting pressure is adjusted too high. Countermeasures: Readjust the compression of the spring.

(2) The valve disc and valve seat are stuck. Because the safety valve has not operated for a long time and has not been regularly inspected and repaired, it has rusted, causing the valve disc to adhere to the valve seat. Countermeasures: Regularly perform manual deflation or water release tests on the safety valve, and pay attention to moisture-proofing during use.

(3) Internal foreign matter is stuck, and the valve disc cannot overcome the obstacle and rise, causing the opening pressure to increase or the valve to be unable to open. Countermeasures: Check and remove foreign matter.

(4) External foreign matter is blocked, the external weight of the static weight or lever type safety valve is artificially aggravated, or other reasons prevent the valve disc from opening normally. Countermeasures: Check and remove foreign matter.

(5) The operating temperature decreases, causing the opening pressure to increase. Countermeasures: When adjusting at normal temperature and using it at low temperature, the set pressure value at normal temperature should be slightly lower than the required opening pressure value.

(1) There are impurities between the valve disc and the valve seat sealing surface. Countermeasures: Use a lifting wrench to open the valve several times to flush out impurities or stolen goods;

(2) Damage to the sealing surface. Due to the material, hardness, assembly, etc. of the sealing surface, the sealing surface may be deformed or misaligned during the safety valve's take-off and return process, or the sealing surface may expand and deform due to temperature changes in the sealing medium, which may lead to medium leakage. Countermeasures: Select a safety valve of appropriate material based on the nature of the sealing medium, possible temperature changes, etc. Defects or damage to the sealing surface of the safety valve should be repaired by grinding, turning and then grinding depending on the situation. At the same time, pay attention to grinding. way to prevent grooves from appearing.

(3) Gasket damage. If the sealing gasket is damaged due to impurities or hard objects stuck, squeezed, or pressed, replace it with a qualified gasket. At the same time, pay attention to cleaning the installation location and installation objects first when placing the gasket;

(4) The valve stem is bent and tilted, causing the valve disc and valve seat to be misaligned. Countermeasures: Reassemble or replace;

(5) The elasticity of the spring is reduced or lost. Because the spring is corroded by the medium or the temperature of the medium increases, the spring becomes soft, the preload force is reduced, and leakage occurs. Countermeasures: Strengthen spring anti-corrosion and heat insulation measures, replace springs in time or readjust opening pressure.

(6) The spring is broken. Countermeasure: Replace the spring.

(7) Improper assembly or improper size of related parts. During the assembly process, the valve core and valve seat are not completely aligned or there is light transmission on the joint surface. The reason is that the sealing surface of the valve core and valve seat is too wide, which is not conducive to sealing. Countermeasures: Check the size and uniformity of the matching gap around the valve core, and ensure that the center hole of the valve core and the sealing surface are aligned; check that the clearance between each part is not allowed to lift the valve core; the drawing requires that the width of the sealing surface be appropriately reduced to achieve effective sealing.

(8) The joint surface of the valve body leaks, and the tightening force of the bolts on the joint surface is insufficient or biased, resulting in poor sealing of the joint surface; the sealing gasket on the joint surface of the valve body does not meet the standards. Countermeasures: Adjust the bolt tightening force. When tightening the bolts, be sure to tighten them diagonally. It is best to measure the gaps while tightening, tighten the bolts until they stop, and make the gaps consistent across the joint surface. Secondly, standard gaskets should be used.

(9) The contact between the valve stem and the valve disc is corroded, causing the valve disc to lose its self-seating ability. When the exposed valve stem is disturbed, the valve disc will deflect, causing sealing failure and leakage. Countermeasures: Regularly check the contact groove between the valve stem and the valve disc, and take reasonable anti-rust measures.

(10) The set pressure is too close to the equipment working pressure. Since the equipment working pressure fluctuation range is close to or exceeds the sealing pressure of the safety valve, leakage may occur. Countermeasures: Select an appropriate safety valve and set the safety valve setting pressure reasonably.

(1) The spring stiffness is too large, the valve disc cannot rise to the opening height, the discharge volume is too small, and the pressure continues to rise after the safety valve is opened, causing it to reopen. The countermeasure is to use a spring with appropriate stiffness;

(2) The adjustment ring is improperly adjusted and the channel area is too large. After the safety valve is opened, the pressure drops sharply below the working pressure. The valve will close with the violent impact of the valve disc on the valve seat. Since the source of the pressure increase has not been eliminated, The valve flap opens again, causing a frequency jump. Countermeasures: Readjust the position of the adjustment ring.

(3) The resistance of the discharge pipeline is too large, and the momentum of the outflowing medium decreases sharply, resulting in excessive discharge back pressure. Countermeasures: Reduce the resistance of the discharge pipe and remove obstacles in the discharge pipe.

(4) The valve is used improperly and the valve discharge capacity is too large. Countermeasures: Make the rated displacement of the selected valve as close as possible to the necessary discharge of the equipment.

The pressure continues to rise after exhausting. This is mainly:

(1) The displacement of the selected safety valve is smaller than the safety relief capacity of the equipment. After the safety valve is opened, there is no time to drain the overpressure medium, and the pressure of the pressure vessel continues to rise. Countermeasures: Re-select a suitable safety valve.

(2) The center line of the valve stem is incorrect or the spring is rusty, which prevents the valve disc from rising to the desired height, resulting in a reduction in the discharge volume of the safety valve. Countermeasures: Reassemble the valve stem or replace the spring, and pay attention to the anti-rust measures of the spring;

(3) The cross-section of the exhaust pipe is insufficient, causing the safety valve displacement to be less than the safe discharge volume of the equipment. Countermeasures: Use an exhaust pipe that meets the safe discharge area.

(4) The spring level does not meet the requirements. Because the stiffness is too small, the spring compression amount is too large during adjustment, resulting in insufficient opening height. Countermeasures: Replace the spring with the corresponding level, and the spring stiffness should be appropriate.

The valve disc does not return to its seat after discharge. This is mainly:

(1) The spring bends the valve stem and the valve disc is installed in an incorrect position or is stuck. Countermeasures: Reassemble, carefully inspect the moving parts for defects such as bruises, naps, rust or burrs, and remove them in time.

(2) The safety valve spring broke during use. After opening, the broken point was misplaced, causing the valve disc to fail to return to its seat normally. Countermeasures: Replace new springs in time.

The nominal pressure is selected based on the operating temperature, valve material and maximum operating pressure.

The working pressure level is selected according to the design temperature and design pressure of the pressure vessel. The working pressure level of the spring and the working pressure of the safety valve have different meanings. The working pressure level of a spring refers to the working pressure range that a certain spring is allowed to use. Within this pressure range, the opening pressure (that is, the set pressure) of the safety valve can be adjusted by changing the preload compression amount of the spring. The working pressure of the safety valve refers to the static pressure in front of the safety valve during normal operation, which is the same as the working pressure of the protected system or equipment. Safety valves with the same nominal pressure can be divided into many different working pressure levels according to spring design requirements. When selecting a safety valve, the working pressure level of the valve should be determined based on the required opening pressure value.

The discharge pressure of the steam boiler safety valve is 1.03 times the set pressure, and the discharge pressure of the safety valve is generally 1.1 times the set pressure (opening pressure).

When selecting the material of the safety valve, various factors such as the working temperature and working pressure of the medium, the performance of the medium, the processability of the material, and the economy should be considered.

Determined based on the required discharge amount, the discharge capacity of the safety valve ≥ the necessary discharge amount. The necessary discharge amount of the protected system refers to the amount that must be discharged to prevent overpressure when abnormal overpressure occurs in the system. It is determined by the working conditions, capacity of the system or equipment, and factors that may cause overpressure.

The heavy hammer lever safety valve uses a heavy hammer and a lever to balance the force acting on the valve disc. According to the lever principle, it can use a weight with a smaller mass 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 mass of the weight).

advantage

shortcoming

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The pulse safety valve is composed of a main valve and an auxiliary valve. The pulse action of the auxiliary valve drives the action of the main valve. Its structure is complex and it is usually only suitable for boilers and pressure vessels with large safety relief volumes.

advantage:

shortcoming:

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Spring-type safety valves use the force of a compression spring to balance the force acting on the valve disc. The compression amount of the spiral coil spring can be adjusted by turning the adjusting nut on it. Using this structure, the opening (setting) pressure of the safety valve can be corrected as needed.

advantage:

shortcoming:

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The valve cover of the open safety valve is open, allowing the spring chamber to communicate with the atmosphere, which is beneficial to reducing the temperature of the spring. It is mainly suitable for containers where the medium is steam and high-temperature gases that do not pollute the atmosphere.

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

When a fully enclosed safety valve is exhausted, all gas is discharged through the exhaust pipe, and the medium cannot leak to the outside. It is mainly used in containers with toxic and flammable gases as the medium.

The opening height of a full-open safety valve is greater than or equal to 1/4 of the flow channel diameter. The discharge area of ​​a full lift safety valve is the minimum cross-sectional area of ​​the valve seat throat. Its action process is a two-stage action type, and it must rely on a lift mechanism to achieve full opening. The full opening safety valve is mainly used in gas medium situations.

The opening height of the micro-lift safety valve is less than 1/4 of the flow channel diameter, usually 1/40 to 1/20 of the flow channel diameter. Its action process is proportional action, mainly used in liquid situations, and sometimes also in gas situations with very small emissions.

This type of safety valve can be divided into safety valves with power auxiliary devices and pilot-operated safety valves.

Safety valve with power assist device: With the help of a power assist device, the safety valve is forced to open when the pressure is lower than the normal opening pressure. It is suitable for occasions 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 out stuck or frozen media. At the same time, it also provides a means to force the safety valve to open in an emergency.

Pilot-operated safety valve: It 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 forms of valves are also used. 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 for sealing, or it can impose a much larger mechanical load on the valve disc than the direct-acting safety valve, so it has good sealing performance. At the same time, its action is rarely affected by back pressure. The disadvantage of this safety valve is that its reliability is related to the main valve and pilot valve, its action is not as fast and reliable as the direct-acting safety valve, and its structure is more complex.

The direct-acting safety valve is opened under the direct action of the working medium, that is, it relies on the pressure of the working medium to overcome the mechanical load imposed on the valve disc by the loading mechanism to open the valve.