Common failures of boiler safety valves and solutions
The boiler safety valve is one of the most important safety accessories to ensure the safe operation of the boiler. Whether it can be opened accurately and reliably is of great significance for maintaining the safe operation of the boiler.
As a valve with important protection functions, safety valves are widely used in various pressure vessels and piping systems. When the pressure vessel (system) reaches the upper limit of the specified pressure tolerance, it can automatically open Discharge the excess medium out of the pressure vessel (system) and close it automatically after the discharge, to ensure that the pressure vessel can operate within a safe and reliable pressure allowable range and avoid major safety accidents. The normal operation of the safety valve is not only related to the normal safe use of pressure vessels such as boilers, but also directly related to the safety of the people's lives and property. Therefore, we must pay high attention to the common failures of boiler safety valves and resolve them in a timely manner.
1. Safety valve leak
Valve leakage is one of the most common faults in boiler safety valve failures. It mainly refers to the leakage of the valve flap and valve seat seal that exceeds the allowable level under normal working pressure of the boiler.
The cause of the fault and its solution:
① Dirt falls on the sealing surface. You can use a lift wrench to open the valve several times to wash away the dirt; ② The sealing surface is damaged. It should be repaired by grinding or turning after grinding according to the degree of damage. After repair, the flatness of the sealing surface should be ensured, and its smoothness should not be less than 10; ③ Due to improper assembly or pipeline load, the concentricity of the parts is destroyed. The additional load of the pipeline should be reassembled or removed; ④ The opening pressure of the valve is too close to the normal pressure of the equipment, so that the sealing surface is lower than the specific pressure. When the valve is subject to vibration or medium pressure fluctuations, leakage is more likely to occur. The cracking pressure should be properly adjusted according to the strength of the equipment; ⑤ The relaxation of the spring reduces the set pressure and causes valve leakage. It may be caused by high temperature or corrosion. Measures such as spring replacement or even valve replacement should be taken. If it is caused by improper adjustment, just tighten the adjustment screw properly.
2. The seat pressure of the safety valve is too low
The cause of the fault and its solution:
Low reseating pressure will cause a large amount of medium to be discharged over time and cause unnecessary energy loss. The reason is that the steam discharge on the spring pulse safety valve is large. After this type of impulse safety valve is opened, the medium is continuously discharged and vibrates The front and back forces of the safety valve body or impulse safety valve continue to increase due to insufficient medium discharge of the main safety valve, so the steam in the pulse tube continues to flow to the impulse safety valve along the gas collecting header in the steam drum to maintain the action of the impulse safety valve. On the other hand, due to the action of this type of impulse safety valve, the sealing surface of the impulse safety valve. After its reorganization forms a kinetic energy pressure area, the valve core is raised, so that the impulse safety valve continues to discharge, the greater the steam discharge, the greater the safe upward thrust acting on the valve core, the smaller the impulse safety valve is, and the easier it is to seat. . At this time, the way to eliminate this fault is to close the throttle valve to reduce the flow of medium flowing out of the impulse safety valve and reduce the pressure in the kinetic energy pressure zone, so that the impulse safety valve is seated. The second factor that causes the low seating pressure is that the cooperation clearance between the valve core and the guide sleeve is not suitable, and the cooperation clearance is too small. After the impulse safety valve is opened, the throttle is instantaneously throttled at this location to form a higher kinetic energy pressure area. The method of lifting and delaying the reseating time is to carefully check the size of each part of the valve core and the guide sleeve. If the clearance is too small, reduce the diameter of the valve flap cover or the diameter of the valve flap steam cap or increase the valve flap and guide. The radial gap between the sleeves increases the flow area of this part, so that the steam flow path does not divide, and the local pressure forms a high kinetic energy pressure zone.
3. Leakage on the joint surface of the valve body
The leakage of the joint surface of the valve body mainly refers to the leakage phenomenon at the joint surface between the upper and lower valve bodies.
The cause of the fault and its solution:
One is that the bolts of the joint surface are not tight enough or tightly biased, resulting in a poor sealing of the joint surface. The elimination method is to adjust the bolt tightening force. When tightening the bolt, it must be tightened diagonally. It is best to measure the gap everywhere while tightening, tighten the bolt until it is not tight, and make the joint surface gap. Consistent. Second, the toothed gasket on the joint surface of the valve body does not meet the standard. For example, there are slight groove marks in the radial direction of the toothed gasket, poor parallelism, and defects such as over-sharpness or over-slope of the tooth shape, which can cause seal failure. So that the valve body joint surface leaks. The quality of spare parts should be checked during maintenance, and the use of standard tooth seals can avoid this phenomenon. The third is that the flatness of the joint surface of the valve body is too poor or it is cushioned by hard impurities, resulting in seal failure. If the flatness of the joint surface of the valve body is too poor to cause leakage of the joint surface of the valve body, the method of elimination is to disintegrate the valve and regrind the joint surface until it meets the quality standards. If the seal fails due to the padding of impurities, carefully clean the joint surface during the assembly of the valve to avoid the impurities falling into it.
4. Delayed return of safety valve
The main performance is that the delay time of the main safety valve is too large after the impulse safety valve is seated.
The cause of the fault and its solution:
The main reasons for this failure are the following two aspects. On the one hand, the amount of steam leakage in the piston chamber of the main safety valve, although the impulse safety valve is seated, the pressure of the steam in the pipeline and the piston chamber is still very high, and the force pushing the piston down is still very large. Therefore, the main safety valve is sluggish. The method to eliminate this fault is mainly solved by opening the throttle valve and increasing the throttle aperture. The opening of the throttle valve and the increase of the throttle hole make the steam remaining in the pulse tube quickly discharged , Thereby reducing the pressure in the piston, so that the thrust acting on the piston downward movement is rapidly reduced, and the valve core is quickly returned by the upward thrust of the steam medium in the header and the upward tension of the main safety valve’s spring seat. On the other hand, the reason is that the friction between the moving parts of the main safety valve and the fixed parts is too large, which will cause the main safety valve to return to the seat slowly. The solution to this problem is to match the clearance between the moving parts of the main safety valve and the fixed parts. The standard range of the console.
5. Safety valve flutter
The chattering phenomenon of the safety valve during the discharge process is called chattering of the safety valve. The occurrence of chattering phenomenon is very likely to cause fatigue of the metal, reduce the mechanical performance of the safety valve, and cause serious hidden dangers to equipment.
The cause of the fault and its solution:
The main causes of chattering are the following: on the one hand, the improper use of the valve, the discharge capacity of the selected valve is too large, and the method of elimination should be to make the rated displacement of the selected valve as close as possible to the necessary discharge of the equipment. On the other hand, because the diameter of the inlet pipe is too small, smaller than the inlet diameter of the valve, or the resistance of the inlet pipe is too high, the method of elimination is to make the inner diameter of the inlet pipe not less than the inlet diameter of the valve when the valve is installed, or reduce the inlet pipe diameter. Resistance, the resistance of the discharge pipe is too large, and excessive back pressure during discharge is also a factor that causes valve flutter, which can be solved by reducing the resistance of the discharge pipe.
