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Five situations of valve leakage and Its Countermeasures
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·Five situations of valve leakage and Its Countermeasures
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Five situations of valve leakage and Its Countermeasures

In the use of daily valves, various failures are often encountered. The valve body and bonnet leakage of the valve are one of many failures. Do you know the cause of this phenomenon? Let us analyze the causes and countermeasures of valve leakage.


1. Leakage of valve body and bonnet


► Reason:


1. The casting quality of cast iron parts is not high, and there are defects such as sand holes, loose structures and slag inclusions on the valve body and the valve cover body;


2. Day freezing crack;


3. Poor welding, there are defects such as slag inclusion, unwelded, stress cracking;


4. The cast iron valve is damaged by heavy objects.


► Maintenance method:


1. Improve the quality of casting, and carry out the strength test strictly according to the regulations before installation;


2. For valves with temperatures below 0° and below 0°, heat or heat should be applied. Valves that are stopped should be excluded from water accumulation;


3. The welds of the valve body and bonnet composed of welding shall be carried out in accordance with the relevant welding operation procedures, and the flaw detection and strength test shall be carried out after welding;


4. It is forbidden to push and put heavy objects on the valve. It is not allowed to hit the cast iron and non-metal valves with the hammer. The installation of the large diameter valve should have the bracket.


► Specific treatment methods for valve body leakage:


Bonding method


Using the characteristics of fast curing speed of the adhesive, the adhesive is coated with the adhesive in a timely manner to form a new solid sealing structure to achieve the purpose of stopping leakage. It is a method of using a special function of the adhesive to carry out pressure plugging.


For the pressure medium and the part of the sand hole with a small leakage, the metal luster can be polished near the leak point, and then the taper pin is used to align the leak point, and the force is entered.


During operation, the pressing mechanism is fixed on one side of the regulating valve, and the screw is pressed at a high speed so that the axial direction of the pressing screw is opposite to the leakage point, and the pressing screw is rotated, and the rivet at the end of the pressing screw is firmly pressed against the leakage. On the part, force the leak to rest.


2. Welding method


A) When the leakage medium pressure of the valve body is low and the leakage is small, a nut with an inner diameter larger than twice the leakage point can be used to allow the leakage medium to flow out of the nut and weld the nut to the valve body. Then, use a bolt with the same specifications as the nut. Place a rubber pad or asbestos pad on the bottom of the nut and screw the top of the bolt into the nut to prevent leakage.


For the valve body with high leakage pressure and large leakage, the drainage welding method can be used. First, use a piece of iron plate, a circular hole is opened in the middle, and an isolation valve with a diameter corresponding to the round hole is welded to the round hole of the iron plate, the isolation valve is opened, and the central hole of the iron plate is aligned with the leakage point to the valve body. Let the leaking medium flow out through the central hole of the iron plate and the isolation valve.


B) The high temperature and high pressure of the leakage medium of the valve body, but the adjustment valve has a large shape size and the leakage amount is not large, and the welding method can also be used.


Firstly, the gap between the valve body and the leaking point is directly welded (no soldering point), and then the length of the tube according to the working condition (working temperature, pressure) depends on the site environment (generally about 200mm) The diameter should be larger than the leak point. A regulating valve adapted to the pipe is welded to one end of the pipe, and the valve is fully opened. Then the other end of the pipe is aligned with the leak point and welded, and the closed regulating valve can be stopped. leakage.


If the bonding surface is not good, a rubber or asbestos pad can be placed on the bonding surface, and then the valve body is welded to the valve body, and then the isolation valve can be closed to achieve the purpose of resealing.


Analysis of five conditions of valve leakage and countermeasures


Second, the leak at the filling


The leakage of the valve, the proportion of the filler is the largest


► Reason:


1. The filler is not selected correctly, is not resistant to the corrosion of the medium, and is not resistant to the use of high pressure or vacuum, high temperature or low temperature of the valve;


2. The filler is not installed correctly, and there are defects such as small generation, poor spiral coiled joints, tightness and looseness;


3. The filler exceeds the service life, has aged, and loses its elasticity;


4. The valve stem has low precision and defects such as bending, corrosion and wear;


5. The number of packing turns is insufficient, and the gland is not pressed;


6. The gland, bolts, and other components are damaged, so that the gland cannot be pressed;


7. Improper operation, excessive force, etc.;


8. The gland is skewed, and the gap between the gland and the valve stem is too small or too large, causing the stem to wear and the packing to be damaged.


► Maintenance method:


1. The material and type of filler should be selected according to working conditions;


2. According to the relevant regulations, the packing should be installed correctly. The packing should be placed in a ring-by-turn manner, and the joint should be 30 ° C or 45 ° C;


3. Filling materials that are too long, aging, and damaged should be replaced in time;


4. After the valve stem is bent and worn, it should be straightened and repaired. If the damage is serious, it should be replaced in time;


5. The packing should be installed according to the specified number of turns, the gland should be tightly and symmetrically tightened, and the press sleeve should have a pre-tightening clearance of more than 5 mm;


6. Damaged glands, bolts and other components shall be repaired or replaced in time;


7. The operating procedures should be observed, except for the impact handwheel, which is operated at a constant normal speed;


8. The gland bolt should be tightened evenly and symmetrically. The gap between the gland and the valve stem should be too small. The gap should be increased properly. The gap between the gland and the valve stem should be too large and should be replaced.


Third, the leakage of the sealing surface


► Reason:


1. The sealing surface is unevenly ground and cannot form a tight line;


2. The top of the joint between the valve stem and the closing member is suspended, not worn or worn;


3. The valve stem is bent or improperly assembled, causing the closing member to be skewed or not in the middle;


4. The quality of the sealing surface material is improperly selected or the valve is not selected according to working conditions.


► Maintenance method:


1. Correctly select the materials and types of the underlying gasket according to the working conditions;


2. The bolt should be screwed evenly and symmetrically. If necessary, a torque wrench should be used. The pre-tightening force should meet the requirements and should not be too large or small. There should be a certain pre-tightening clearance between the flange and the threaded joint;


3. The gasket assembly should be aligned in the middle, the force is even, the gasket is not allowed to overlap and use the double gasket;


4. Static sealing surface corrosion, damage processing, processing quality is not high, should be repaired, polished, coloring inspection, so that the static sealing surface meets relevant requirements;


5. When installing the gasket, pay attention to cleaning. Apply kerosene to the sealing surface. The gasket should not fall to the ground.


Fourth, the leak at the joint of the seal


► Reason:


1. The sealing ring is not pressed;


2. The sealing ring is welded to the body, and the quality of the surfacing is poor;


3. The sealing ring is connected with thread, screw and pressure ring;


4. The seal is connected and corroded.


► Maintenance method:


1. Leakage at the sealing pressure should be injected and fixed by pressing the adhesive;


2. The sealing ring should be repaired by the welding specification. The original surfacing and processing shall be removed when the surfacing is unable to repair the welding;


3. Remove the screws and pressure ring to clean, replace the damaged parts, grind the sealing and sealing joints, and reassemble. For parts with large corrosion damage, they can be repaired by welding or bonding;


4. The sealing surface of the sealing ring is corroded and can be repaired by grinding or bonding. If it cannot be repaired, the sealing ring should be replaced.


5. The closing piece falls off and leaks.


► Reason:


1. Poor operation, causing the closing member to be stuck or exceeding the top dead center, and the joint is damaged and broken;


2. The closing parts are not firmly connected, loose and fall off;


3. The material of the connecting piece is not correct, and it cannot withstand the corrosion of the medium and mechanical wear.


► Maintenance method:


1. Correct operation, the valve can not be used too much force, open the valve can not exceed the top dead center, after the valve is fully open, the hand wheel should be reversed a little;


2. The closing piece should be firmly connected to the valve stem, and the threaded joint should have a stop piece;


3. The fasteners used to connect the closing member to the valve stem should withstand the corrosion of the medium and have certain mechanical strength and wear resistance.


The above is the five cases of valve leakage summarized by Xiaobian and the countermeasures. I hope to help everyone.