Monday, August 23, 2010

Analysis of common failures of boiler safety valve (b)

The elimination of the adjustment bolt is tight, and when the bear bolted diagonal according to the tight manner, preferably while tight space around edge measurement will bolt fixed tight to tight, the combination of surface and throughout the gap unanimously. Second, combination valve gasket surface profile does not meet the required standards. For example, the radial profile gasket marks a slight groove, parallel difference, too sharp or too tooth defects such as the slope will cause seal failure. Surface so that the combination valve leakage. In the overhaul of spare parts when a good quality of the tooth using standard gasket on the occurrence of this phenomenon can be avoided. Third, body surface flatness combined with poor or live in hard-pad caused by impurities in seal failure. Combination of body surface as a result of the flatness combined with poor body surface caused by leakage, the method is to eliminate valve combined with the disintegration of re-grinding surface until it meets the quality standards. Pad as a result of impurities in seal failure caused by living in the valve assembly when the combination of carefully cleaning the surface to avoid falling into the hands of impurities.



2.3, impulse action先自safety valve safety valve does not move



This phenomenon is commonly referred to as the main security door and refuse to move. Refusing to move the main security door in the operation of the boiler to run against is very large, the equipment is a major risk, seriously affecting the safe operation of equipment, once in the operation of the pressure vessel and the medium pressure pipeline in more than ratings, the main security gate do not move, so that equipment can easily run overpressure damage caused by equipment and major incident.



The analysis of the main security gate before the reasons for refusing to move, first of all analyze the main security door action principle. Figure 1, when the pressure within the pressure vessel up to the whole impulse pressure safety valve, safety valve impulse moves through the medium from the container into the main pipeline valve piston room, the Pistons will have a small indoor expansion step-down, if the piston chamber pressure at this time for the P1, the piston area of expenditure Shs, this time on the role of f1 in the piston is:



F1 = P1 × Shs ... ... ... ... ... ... ... ... (1)



?? If this time the pressure containers for medium pressure P2, the area of spool Sfx, is now a medium on the spool upward force f2 as follows:



F2 = P2 × Shx ?..............( 2)



Normally a safety valve spool piston diameter than the diameter, so-style (1) and type (2) Shs> Sfx? P1 ≈ P2



If spring up through the stem of the valve core is set to f3 and the rally will be moving parts and friction between the fixed parts (mainly the piston and the friction between the piston chamber) as fm, while the main security door a prerequisite for action: only the role of the force in the piston slightly larger than the role of f1 in the spool so that the upward spring force f2 and upward through the stem of the spool tension f3 and moving parts and friction between the fixed parts (mainly the piston and friction between the piston chamber) fm and time of that: f1> f2 + f3 + fm am to start the main security gate.



Through practice, the main security door and refused to move the following three main factors:



First, there are moving parts valve resistance phenomenon card. This may be due to improper assembly, or mixed with dirt and impurities parts corrosion; piston chamber poor surface finish, surface damage, there are groove marks, such as hardware defects. This will enable the moving parts and fixed parts fm between the friction increases, other conditions remain unchanged in case of f1 <f2 + f3 + fm therefore refused to move the main security gate.



For example, in 2001, before the 3rd overheated furnace overhaul the main security door steelyard weight test run, the occurrence of the main security door refused to move. When the dissolution of maintenance inspection found that the Pistons have a lot of rust indoor dirt and impurities, the Pistons could not campaign in the interior piston, resulting in the main security door refused to move. Maintenance on the piston, and piston ring expansion room to deal with the rust, groove marks on the piston chamber defects, such as grinding, assembly room wall before the Pistons lead powder coated evenly and strictly carried out in sequence on the valve assembly. When the boiler pressure test on the pulse tube for washing, and then the main security gate valve connected with the impulse, overhaul furnace after the point when the safety re-run all the normal tests steelyard weight. 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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