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. The hard seal V-shaped ball valve has V-shaped core and surfacing hard alloy. The metal seat has a strong shear force, which is especially suitable for media containing fibers and tiny solid particles. The multi-way ball valve not only can flexibly control the confluence, splitting, and flow direction switching of the medium, but also can close any channel and connect the other two channels. This type of valve should generally 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 the nominal pressure, the duration is not less than 5 min, and the valve casing and the packing should be free of leakage. In the rigorous test, the test pressure is 1.1 times of the nominal pressure; the test pressure shall meet the requirements of GB 50243 during the duration of the test, and the leakage of the valve sealing surface shall be qualified.
The visual inspection must be carried out before the valve is installed. The nameplate of the sanitary ball valve should comply with the current national standard "General Valve Mark" GB 12220. For valves with a working pressure greater than 1.0 MPa and a shut-off effect on the main pipe, the strength and tight performance tests shall be carried out before installation, and shall be used after passing the test.
Causes of leakage of valve body and bonnet:
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, freezing and cracking;
3, poor welding, there are defects such as slag inclusion, unwelded, stress cracks;
4. The cast iron valve is damaged after being hit by heavy objects.
Maintenance method:
1. Improve the casting quality and conduct the strength test strictly according to the regulations before installation;
2. For valves with temperatures below 0 °C and below 0 °C, 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.
Reasons for leakage of the sealing surface:
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, so that the closing member is 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 inverted gasket according to the working conditions;
2, carefully adjusted, smooth operation;
3. 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;
4, the gasket assembly should be aligned in the middle, the force is even, the gasket is not allowed to overlap and use double gasket;
5, 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;
6. When installing the gasket, pay attention to cleaning. Apply kerosene to the sealing surface. The gasket should not fall to the ground.
The leakage of the leakage valve at the packing, the proportion of the filler is large. The reason is generally:
1. The filler is not used correctly, it is not resistant to the corrosion of the medium, and is not resistant to high pressure or vacuum, high temperature or low temperature.
2, the filler is not installed correctly, there are defects such as small generation, poor spiral coiled joints, tight and loose;
3. The filler exceeds the service life, has aged, and loses its elasticity;
4, the valve stem accuracy is not high, there are defects such as bending, corrosion, wear;
5. The number of packing rings 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 valve stem to wear and the packing to be damaged.
Maintenance method:
1. The materials and types of fillers should be selected according to the working conditions;
2. Install the packing correctly according to the relevant regulations. 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 5mm;
6. Damaged glands, bolts and other components shall be repaired or replaced in time;
7, should comply with the operating procedures, in addition to the impact of the hand wheel, at a constant speed normal operation;
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.
Well, the above is the sharing of the precautions for the construction and installation of the
diaphragm valve as well as the common problems and maintenance methods. I hope that everyone can help.
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