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HomeNewsDiaphragm valve construction and installation precautions and common problems and maintenance methods

Diaphragm valve construction and installation precautions and common problems and maintenance methods

2020-10-05
Diaphragm Valve construction and installation precautions and common problems and maintenance methods



Diaphragm valve connection type: flange structure or welding is mainly used to cut off or connect the medium in the pipeline, and can also be used for fluid regulation and control. Among them, the hard sealing V-type Ball Valve has strong shear force between its V-shaped ball core and the metal valve seat of hardfacing alloy, which is especially suitable for medium containing fiber and small solid particles. The multi-way ball valve can not only flexibly control the confluence, shunt and flow direction switching of medium, but also close any channel to connect the other two channels. This kind of valve should be installed horizontally in the pipeline. Ball valve classification: Pneumatic Ball Valve, Electric Ball Valve, manual ball valve.



In the strength test, the test pressure is 1.5 times of the nominal pressure, and the duration is not less than 5min. The valve shell and packing are qualified if there is no leakage. During the tightness test, the test pressure shall be 1.1 times of the nominal pressure; the test pressure shall meet the requirements of GB 50243 during the test duration, and the valve disc sealing surface without leakage shall be regarded as qualified.



Before the valve is installed, the appearance inspection must be carried out, and the name plate of sanitary ball valve shall comply with the provisions of the current national standard general valve marking (GB 12220). For the valve with working pressure greater than 1.0 MPa and cutting off on the main pipe, strength and tightness test shall be conducted before installation, and the valve can be used only after passing the test.



Leakage causes of valve body and valve cover:

1. The casting quality of iron castings is not high, and there are sand holes, loose structure, slag inclusion and other defects on the valve body and valve cover body;



2. The weather is cold and cracked;



3. Poor welding, slag inclusion, non welding, stress crack and other defects exist;



4. The cast iron valve was damaged after being hit by heavy objects.

Maintenance method:



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



2. For valves with air temperature below 0 ℃ and below, heat preservation or heat mixing shall be carried out, and stagnant water shall be removed from valves that are not in use;



3. The welding seams of valve body and valve cover composed of welding shall be carried out according to relevant welding operation regulations, and flaw detection and strength test shall be conducted after welding;



4. It is forbidden to push or place heavy objects on the valve. It is not allowed to strike cast iron and non-metallic valves with a hammer. The installation of large-diameter valves should have supports.

Leakage reason of sealing surface:



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



2. The top center of the connection between the valve rod and the closing part is suspended, not in alignment or worn;



3. The valve rod is bent or assembled improperly, so that the closing part is skewed or out of alignment;



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



Maintenance method:

1. The material and type of bumping Gasket should be selected correctly according to the working conditions;



2. Careful adjustment and smooth operation;



3. The bolts should be evenly and symmetrically screwed. If necessary, the 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 flange and thread connection;



4. The gasket assembly should be aligned with the center, and the stress is uniform. The gasket is not allowed to overlap and use double gasket;



5. If the static sealing surface is corroded, damaged, and the processing quality is not high, repair, grinding and coloring inspection should be carried out to make the static sealing surface meet the relevant requirements;



6. When installing the gasket, attention should be paid to cleaning, the sealing surface should be cleaned with kerosene, and the gasket should not fall on the ground.

The leakage at the packing, the leakage of the valve, the proportion of the packing place is larger than Zui. The reasons are generally:



1. Packing selection is not correct, not resistant to medium corrosion, not resistant to valve high pressure or vacuum, high temperature or low temperature use;



2. The packing is not installed properly, and there are some defects, such as replacing the big with the small, the spiral winding joint is not good, and the tightening is loose;



3. The filler is out of service life, has aged and lost elasticity;



4. The precision of the valve rod is not high, and there are bending, corrosion, wear and other defects;



5. The number of packing rings is insufficient, and the gland is not compressed;



6. The gland, bolts and other parts are damaged, which makes the gland unable to be pressed tightly;



7. Improper operation, excessive force, etc;



8. The gap between the gland and the valve stem is too small or too large, resulting in valve rod wear and packing damage.



Maintenance method:



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



2. The packing should be installed correctly according to the relevant regulations. The packing should be placed and compacted one by one, and the joint should be at 30 ℃ or 45 ℃;



3. The fillers with long service life, aging and damage shall be replaced in time;



4. The valve rod should be straightened and repaired after bending and wear, and the seriously damaged valve rod should be replaced in time;



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



6. Damaged gland, bolt and other parts shall be repaired or replaced in time;



7. Besides the impact handwheel, it should be operated with constant speed and normal force;



8. The gland bolts should be evenly and symmetrically tightened. If the clearance between the gland and the valve stem is too small, the clearance should be appropriately increased; if the clearance between the gland and the valve stem is too large, it should be replaced.

Next: Analysis of common problems of pneumatic diaphragm valve

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