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The working principle and function of gate valve:

Gate valves belong to the type of cut-off valves, which are usually installed on pipelines with a diameter greater than 100mm to cut or connect the flow of media in the pipeline. Because the valve flap is a gate type, it is generally called a gate valve. The gate valve has the advantages of labor saving and less flow resistance. However, the sealing surface is easy to wear and leak, the opening stroke is large, and the maintenance is difficult. The gate valve cannot be used as a regulating valve and must be in the fully open or fully closed position. The working principle is: when the gate valve is closed, the stem moves downwards depending on the height of the sealing surface of the gate valve and the sealing surface of the valve seat is smooth and flat, consistent with each other to prevent the flow of media, and rely on the top wedge to increase the sealing effect. The closing member moves along the vertical direction of the center line. There are many types of gate valves, which can be divided into wedge type and parallel type according to the type. Each type is divided into single gate and double gate.

Gate valve structure:

     Gate valve body adopts self-sealing form. The connection method of the valve cover and the valve body is to use the upward pressure of the medium in the valve to force the sealing packing to be compressed to achieve the purpose of sealing. Gate valve sealing packing is sealed with high-pressure asbestos packing with copper wire.

     The structure of the gate valve is mainly composed of the valve body, bonnet, frame, valve stem, left and right valve flaps, packing sealing device, etc.

     The valve body material is divided into carbon steel and alloy steel according to the pressure and temperature of the pipeline medium. Generally installed in the valve of superheated steam system, t> 450 ℃ or more, the valve body is alloy material, such as boiler exhaust valve. For the valve installed in the water supply system or the pipeline with medium temperature t≤450 ℃, the valve body material is carbon steel.

     Gate valves are generally installed on DN ≥ 100 mm soda pipes. The nominal diameter of the gate valve of the WGZ1045 / 17.5-1 boiler in the first phase of Zhangshan includes DN300, DNl25 and DNl00.

Gate valve maintenance quality standard

Gate valve body:

1. The valve body should be free from defects such as trachoma, cracks and erosion, and should be dealt with in time after discovery.

2. There should be no debris in the valve body and pipeline, and the entrance and exit are unblocked.

3. The thread plug at the bottom of the valve body should ensure reliable sealing and no leakage.

Stem of gate valve:

1. The curvature of the valve stem should not be greater than 1/1000 of the total length, otherwise it should be straightened or replaced.

2. The trapezoidal thread part of the valve stem should be intact, without breakage, snapping and other defects, and the amount of wear should not exceed 1/3 of the thickness of the trapezoidal thread.

3. The surface is smooth and free of rust, and there is no flake corrosion and surface delamination on the sealing contact with the packing. Those with a uniform corrosion point depth ≥0.25 mm should be replaced with a new one. The finish should be guaranteed above ▽ 6.

4. The connecting thread should be intact and the pin fixed reliably.

5. The cutting rod and the cutting rod nut should be combined to rotate flexibly, without jamming during the whole stroke, and the thread should be coated with lead powder for lubrication protection.

Packing seal:

1. The pressure and temperature of the packing used should meet the requirements of the valve medium, and the product should be accompanied by a certificate of conformity or necessary test identification.

The working principle and maintenance process of the gate valve have a standard, and the quality of the general gate valve is to be guaranteed, just worry

2. Packing specifications should meet the size requirements of the sealed box, and should not be replaced with oversized or undersized packings. The height of the packing should meet the valve size requirements, and the thermal tightness should be set aside.

3. The filler interface should be cut into an oblique shape with an angle of 45 °. The interface of each circle should be staggered by 90 ° -180 °. The length of the filler after cutting should be appropriate. There should be no gaps or superpositions in the interface of the filler box. .

4. Packing seat ring and packing gland should be intact, no rust, the packing box should be clean and smooth, the gap between the door rod and seat ring should be 0.1-0.3 mm, the maximum is not more than 0.5 mm, the outer periphery of packing gland and seat ring The gap with the inner wall of the stuffing box is 0.2-0.3 mm, and the maximum is not more than 0.5 mm.

5. After tightening the hinge bolt, the pressure plate should be kept straight and the tightening force is even. The packing gland and the inner hole of the pressure plate should be consistent with the gap around the valve stem. The packing gland pressed into the packing chamber should be 1/3 of its height dimension.

Sealing surface:

1. After repairing, the sealing surface of the valve disc and valve seat should be free of spots and grooves, the contact part should account for more than 2/3 of the valve flap width, and the surface finish should reach more than ▽ 10.

2. Assemble the test valve flap. After the valve flap is inserted into the valve seat, the valve core should be 5-7 mm higher than the valve seat to ensure the tightness.

3. When assembling the left and right flaps, the self-adjustment should be flexible and the anti-off device should be intact and reliable. 3.5 Valve stem nut:

4. The inner bushing screw should be intact, and there should be no broken or disordered buckles, and the fixing with the outer shell should be reliable and free of looseness.

5. All bearing components should be intact and flexible to rotate. No cracks, rust, heavy skin and other defects on the surface of the inner and outer shells and steel balls.

6. Disc springs should be free of cracks and deformation, otherwise they should be replaced with new ones. 3.5.4 The fixing screws on the surface of the lock nut shall not be loose. The stem nut rotates flexibly, and the axial clearance is guaranteed but not greater than 0.35 mm.