3 is the main safety valve and safety valve mismatch impulse, impulse steam flow valve is too small. Impulse valve nominal diameter is too small, resulting in the piston chamber into the main steam safety valve insufficient to promote the piston downward movement of the force f1 is not enough, that is, f1 <f2 + f3 + fm causing the main valve spool not move. This phenomenon occurred mostly in the main safety valve safety valve-type impulse there is a replacement, due to a result of ill-considered.
For example, No. 5 furnace overhaul in 2002, it will be two heavy hammer-type impulse valve replaced with two valve plant in Harbin, A49H-P54100VDg20 pulsed valve, this valve type generally associated with spring-A42H-P54100VDg125 matched the main safety , it would be produced with the Soviet Union Dg150 × 90 × 250-type old-fashioned main safety valve supporting the use of such a primary safety valve with spring-A29H-P54100VDg125 the main safety valve of this type than the nominal diameter is not only larger but also less air tightness in the No. 5 furnace capacity safety valve set ram is completed, to run ram tests caused by the main safety valve refused to move.
Later we will impulse valve disintegrated, its orientation with the part of the sleeve and spool gap expanded to increase its flow area, once again ran a successful pilot mound. So the impulse valve and the main valve mismatch, the smaller nominal diameter can also cause the main valve to resist moving.
2.4, impulse valve safety valve back seat emperor back seat for too long delay
The major causes of this failure occurs the following two aspects:
On the one hand, the main valve piston chamber the size of the leakage of steam, although the impulse valve back seat, but the existence of the pipeline and the piston chamber of the steam pressure is still high, push the piston downward force is still large, Therefore, the main valve back seat cause retardation, this failure will occur in the A42Y-P5413.7VDg100-type safety valve, because this type of relief valve piston chamber gas seal was good. Ways to eliminate this failure, mainly through large throttle opening and increasing the opening degree of throttle aperture to be resolved, the opening degree of throttle opening and the throttle aperture large increase in both pulse tube remaining in the rapid discharge of steam out , thereby reducing the pressure inside the piston to effect the downward movement in the piston thrust rapidly decreases spool together in the steam box steam media set up its own thrust and the main safety valve under the action of spring pull up quickly to Block.
The other reason is that the main valve of the moving parts and fixed friction between the components is too large can also cause the main valve back seat slow way to solve this problem is to the main safety valve moving parts and fixed parts with the clearance Console standard range.
2.5, low pressure safety valve of the back seat
Low-pressure safety valve back seat to the boiler running a great risk to the economy, back seat pressure is too low will result in a lot of media time-out emissions, resulting in unnecessary energy loss. Such failures have occurred within the 200MW unit used by the A49H-type spring pulse valve, the analysis of the reasons is mainly composed of the following factors:
First, spring safety valve on the pulse of the excretion of large amount of steam, this form of the impulse valve is turned on, the media continue to discharge to promote the main safety valve action.
On the one hand is the impulse valve before the pressure due to the main valve of the media continue to increase in emissions is not enough, so the steam inside the pulse tube gas gathering together along the drum or tank to continue to maintain the flow of impulse impulse valve safety valve action.
On the other hand due to this type of impulse flow of media through the valve spool and the guide sets the gap between the flow of the main valve piston chamber, the medium out of impulse valve sealing surface around the formation of kinetic energy of the pressure in their area, raise the spool, so the impulse to continue to discharge safety valve, steam emissions, the greater the kinetic energy of the pressure zone valve core part of the pressure the greater the role of the upward thrust on the spool the greater the less impulse valve easy to back seat, this time way to eliminate this failure is to throttle off small, so that the media out of impulse decrease in the flow valve to reduce pressure on kinetic pressure of the region, so that impulse valve back seat.
Back seat low pressure caused by the second factor is: spool and the guide sleeve with clearance inappropriate, with the gap is too small, in the impulse valve seat Kai, after an instant savings in this formed part of the kinetic energy of a high pressure zone will be Spool inflate the seat back to the time delay, when the container dropped to low, the kinetic energy pressure area pressure decreases, impulse valve back seat.
To eliminate this failure is to carefully check the spool and the guide cover the various parts of sizes, with the gap over an hour, reducing the valve flap flap valve sealing surface of straight-type gas cap diameter, or increased resistance valve flap and the radial clearance between the guide sleeve , to increase the parts of the flow area, so that the steam flows through it without too much throttle, leaving partial pressure increases the kinetic energy of the formation of a high pressure zone.
Low-pressure caused by back seat, another reason is that the movement part of friction force, some parts of a jam, the solution is to carefully examine all moving parts, strictly in accordance with maintenance standards for maintenance of various components for each of the components adjusted to meet the gap standards, to remove the possibility of jam.
2.6, the frequency of safety valve jump
Frequency-hop refers to the safety valve back seat and after a slightly elevated pressure, turn valve to open, repeated on several occasions, this phenomenon is known as a safety valve, "frequency jump." Mechanical properties required safety valve safety valve movement in the whole process of opening up to the required height, does not allow for card blocking, tremor and frequency jump phenomenon. The frequency jump phenomenon on the valve seal is extremely detrimental to the sealing surface can easily result in the leakage. Analyze the reasons mainly related to the pressure relief valve back to seat up to high-related back to block the pressure is high, the container medium excess emissions less valve seat has been returned, and when the operating personnel to adjust properly, the pressure inside the container will soon be l up, so the valve caused by movements like this can be accessed via the opening degree of throttle opening its way to be removed. Open the throttle, after leading off the main valve piston to reduce the indoor steam source to promote a smaller force the piston downward movement, the main safety valve action less likely, thus avoiding the main safety valve to start a row.
2.7, a safety valve flutter
Safety valve in the discharge occurred during the jitter phenomenon, called a safety valve flutter, flutter easily result in the occurrence of the phenomenon of metal fatigue, so that the mechanical valve performance degradation, resulting in serious risks of equipment occurred chatter because of the following aspects:
On the one hand is the improper use of the valve, the discharge capacity of selected valve too (as opposed to be in terms of emissions), the elimination method is to make use of the valve should be rated for emissions equipment as close as possible the necessary emissions.
On the other hand is due to imports of the pipe diameter is too small, less than the valve diameter of imports, or imports of tube resistance is too large to eliminate valve installation method is to make imports of tube diameter of not less than the valve diameter of imports or to reduce the imports of pipe resistance. Discharge piping resistance is too large, resulting in excessive emissions from the north when the pressure is caused by a factor of flutter valve, you can pipe the resistance by reducing the emissions to be addressed.
3, Conclusion
The boiler safety valve on the causes of common faults were analyzed and put forward concrete solutions, although the boiler safety valve by the primary, secondary valve supporting composition, and mechanical and thermal control of dual protection, and some fault less liable to occur, but only to fully grasp the safety valve to eliminate common failure causes and methods of dealing with them in the event of a failure can be handy in ensuring the safe operation of equipment, has an important significance. ball valve Trunnion Mounted Ball Valve Floating Ball Valve Top Entry Ball Valve Three way ball valve V Type Ball Valve
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