Boiler Safety Valve is one of the most important safety accessories to ensure the safe operation of boiler. Whether it can be opened accurately and reliably is of great significance to maintain the safe operation of boiler.
As a valve with important protection function, safety valve is widely used in various pressure vessels and piping system, when the pressure vessel system reaches the upper limit of the specified pressure bearing value, the pressure vessel can be opened automatically by induction, and the excess medium can be discharged out of the pressure vessel system, and can be closed automatically after discharge, thereby ensuring that the pressure vessel can be operated within the safe and reliable pressure allowable range, 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 people’s lives and properties. Therefore, great attention must be paid to the common failures of the Boiler Safety Valve, and eliminate it in a timely manner.
1. Safety Valve Leak
Valve leakage is one of the most common faults of Boiler Safety Valve. It mainly refers to the leakage between valve disc and valve seat under normal working pressure.
Causes of failures and their solutions:
1) Dirt falls on the sealing surface. Lift wrench can be used to open the valve several times, the dirt washed away.
2) Seal surface damage. According to the degree of damage, the method of grinding or grinding after turning should be used to repair. After repair should ensure the sealing surface smoothness, its smoothness should not be less than 10.
3) Because of Improper Assembly or pipeline load and other reasons, make parts of concentricity damage. Additional pipe loads should be reassembled or eliminated;
4) Valve opening pressure is too close to the normal equipment pressure, so that the sealing surface is lower than the pressure. When the valve is subject to vibration or medium pressure fluctuations, more prone to leakage. The opening pressure should be adjusted according to the equipment strength condition.
5) Loose spring reduces the setting pressure and causes the valve to leak. May be due to high temperature or corrosion and other reasons, should be taken to change the spring, or even change the valve and other measures. If it is caused by improper regulation, it only needs to tighten the adjusting screw properly.
2. Low Return pressure of relief valve
Causes of failures and their solutions:
Low Return pressure will cause a large number of medium to discharge over time, resulting in unnecessary energy loss, the reason is that the spring pulse relief valve on the large amount of steam discharge, this form of impulse relief valve to open, the medium continues to discharge, vibration Relief Valve Body, or impulse relief valve before and after the force due to the main relief valve medium discharge is not enough to continue to increase, so the steam in the pulse tube along the drum gas header continues to flow impulse relief valve action.
On the other hand because of this type of Impulse safety valve action impulse safety valve sealing surface. To its reorganization to form a kinetic pressure zone, the spool will be raised, so that the impulse safety valve continues to discharge, the greater the steam discharge, the role of the Spool on the safety of the thrust on the larger, the Impulse safety valve will be easier to return to the seat. At this point, the way to eliminate the fault is to turn off the throttle valve, so that the flow of the impulse relief valve to reduce the pressure in the kinetic energy pressure zone, so that the impulse relief valve back to seat. The second factor that causes the low return pressure is that the fit clearance between the spool and the guide sleeve is not suitable, and the fit clearance is small, delay Return Time, the way to eliminate this failure is to carefully check the size of the spool also guide sleeve parts, with a small clearance, reduce disc cover directly or disc stop valve cap diameter or increase the disc and guide sleeve radial clearance, to increase the circulation area of the part, so that the steam flow is not diverted when the local pressure to form a high kinetic pressure zone.
3. Body Joint Leakage
Valve body joint surface leakage mainly refers to the upper and lower valve body joint surface leakage phenomenon.
Causes of failures and their solutions:
One is the joint surface of the bolt tight force is not enough or tight partial, resulting in a poor seal joint surface. The elimination method is to adjust the bolt tightening force, in the tight bolt must be held in accordance with the diagonal tightening way, it is best to measure all the side tight side clearance, the bolt tight to do not move so far, and make the joint surface clearance of all places consistent.
Second, the valve body joint surface of the tooth seal gasket does not meet the standard. For example, a slight groove in the radial direction of the tooth seal gasket, poor parallelism, tooth too sharp or slope and other defects will cause seal failure. This causes the valve body joint to leak. In the maintenance of spare parts quality, the use of a standard tooth-shaped gasket can avoid this phenomenon.
Third, the valve body joint plane is too poor or by the hard impurity cushion seal failure. The elimination of body surface leakage due to poor flatness of the body surface is to disassemble the valve and re-grind the joint surface until it meets quality standards. If the seal fails due to impurity packing, carefully clean the joint surface to avoid impurity falling into the valve assembly.
4. Delayed Return of relief valve
The main performance of the impulse relief valve after the return of the main relief valve delayed return time is too large.
Causes of failures and their solutions:
There are two main reasons for this failure. On the one hand, the leakage of the Piston Chamber of the main relief valve is large. Although the impulse relief valve has returned to its seat, the steam pressure in the pipeline and in the Piston Chamber is still very high, and the force pushing the piston down is still very large, this causes the main relief valve to return to the seat slowly. The method of eliminating this kind of trouble is mainly solved by opening the throttle valve wider and enlarging the throttle hole diameter. Both the opening of the throttle valve wider and the increasing of the throttle hole make the steam left in the pulse tube drain away quickly, thus, the pressure in the Piston is reduced, and the thrust force acting on the Piston moving up and down is rapidly reduced. The valve core is quickly returned to the seat under the upward thrust of the steam medium in the header and the upward pull force of the main safety valve spring itself. On the other hand, the friction between the moving parts and the fixing parts of the main safety valve will cause the main safety valve to return to the seat slowly, the solution to this problem is to fit the main relief valve moving parts and fixed parts within the standard clearance console range.
5. Safety Valve Chatter
The vibration phenomenon of safety valve in the process of discharging is called the chatter of safety valve. The chatter phenomenon easily causes metal fatigue, which reduces the mechanical performance of safety valve and causes serious hidden trouble of equipment.
Causes of failures and their solutions:
The main causes of flutter are as follows: On the one hand, the valve is used improperly, the discharge capacity of the valve is too large, the elimination method is that the rated discharge of the valve should be used 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 big, the method of elimination is when the valve is installed, the internal diameter of the inlet pipe should not be less than the inlet diameter of the valve or the resistance of the inlet pipe should be reduced, this can be solved by reducing the resistance of the discharge line.
Post time: Jul-28-2021