Collection of gate valve maintenance process regulations

Gate valves belong to the type of shut-off valves, which are usually installed on pipelines with a diameter greater than 100mm, and are used to cut off or connect the flow of media in the pipeline. Because the valve disc is of the gate type, it is commonly known as the gate valve. Gate valves have the advantages of less effort on and off, and less flow resistance. However, the sealing surface is easy to wear and leak, the opening stroke is large, and the maintenance is difficult. Gate valves cannot be used as control valves and must be in the fully open or fully closed position. The working principle is as follows: when the gate valve is closed, the valve stem moves downward, relying on the sealing surface of the gate valve and the sealing surface of the valve seat to be smooth and smooth, and the sealing surface is consistent with each other, and the top wedge is relied on to increase the sealing effect. The closure moves perpendicular to the centerline. 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 ram and double ram.

The gate valve body is self-sealing. The connection between the bonnet and the valve body is to use the upward pressure of the medium in the valve to compress the sealing packing to achieve the purpose of sealing. The gate valve seal packing is sealed with high-pressure asbestos packing with copper wire.

The gate valve structure is mainly composed of valve body, valve cover, frame, valve stem, left and right valve discs, 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, the valve installed in the superheated steam system is above 450°C t> and the valve body is made of alloy material, such as boiler exhaust valve. The valve installed in the water supply system or the medium temperature t≤450°C pipeline, the valve body material can be carbon steel.

Gate valves are generally installed on DN≥100mm steam pipes. There are three types of nominal diameters of gate valves in Zhangshan Phase I WGZ1045/17.5-1 boiler: DN300, DNl25 and DNl00.

2.1.1 Remove the fixing bolts of the upper frame of the bonnet, unscrew the nuts of the four bolts on the poppet bonnet, rotate the stem nut in the counterclockwise direction to make the valve frame detach from the valve body, and then use a lifting tool to hang the frame down and put it to a suitable part. The stem nut part is to be disassembled and inspected.

2.1.2 Take out the retaining ring at the sealing ring of the valve body, and press down the valve cover with a special tool to create a gap between the valve cover and the four rings. Then take out the quadruple ring in sections. Finally, use a lifting tool to lift the valve cover out of the valve body together with the valve stem and disc. Place it in the maintenance site to prevent damage to the valve disc joint surface.

2.1.3 Clean the inside of the valve body, check the joint surface of the valve seat, and determine the maintenance method. Cover the dismantled valve with a special cover plate or covering, and affix the seal.

2.1.4 Loosen the hinge bolts of the packing box on the valve cover. The packing gland is loosened and the stem is unscrewed.

2.1.5 Disassemble the upper and lower splints of the valve disc frame, take out the left and right valve discs, and keep the internal universal roof and gasket. Measure the total thickness of the gasket and record it.

2.2.1 The joint surface of the Leflow gate valve seat should be ground with special grinding tools (grinding guns, etc.). Grinding can be done with abrasive sand or abrasive cloth. The method is also from coarse to fine, and finally polished.

2.2.2 The valve disc joint surface can be ground by hand or grinding tools, if there are deep pits or grooves on the surface, it can be sent to the lathe or grinder for micro-processing, and all are leveled and polished.

2.2.3 Clean the valve cover and sealing packing, remove the rust on the inner and outer walls of the packing pressure ring, so that the pressure ring can be smoothly inserted into the upper part of the valve cover, which is convenient for pressing and sealing the packing.

2.2.4 Clean the packing inside the valve stem packing box, check whether the internal packing seat ring is intact, the gap between the inner hole and the felling rod should meet the requirements, and the outer ring and the inner wall of the packing box should be free of jamming.

2.2.5 Clean the rust and scale of the packing gland and pressure plate, and the surface should be clean and intact. The gap between the inner hole of the gland and the felling rod should meet the requirements, and the outer wall and the packing box should be free of jamming, otherwise it should be repaired.

2.2.6 The hinge bolt is loose, the thread part should be intact, the nut should be complete, the root of the bolt can be gently screwed by hand, and the pin should rotate flexibly.

2.2.7 Clean the rust on the surface of the valve stem, check whether there is bending, and straighten it if necessary. The trapezoidal thread part should be intact, free of buckle and damage, and coated with lead powder after cleaning.

2.2.8 Clean the quadruple ring, and the surface should be smooth. The flat surface must not have burrs or curls.

2.2.9 The fastening bolts should be cleaned, the nuts should be complete and rotate flexibly, and the thread buckle part should be coated with lead powder.

2.2.10 Clean the stem nut and internal bearing:

(1) Remove the lock nut of the stem nut and the fixing screw of the housing, and unscrew the locking screw in the counterclockwise direction.

(2) Take out the stem nut and bearing, disc spring, and clean with kerosene. Check whether the bearing rotates flexibly and whether there are cracks in the disc spring.

(3) Clean the valve stem nut, check whether the trapezoidal thread of the inner bushing is in good condition, and the fixing screw of the shell should be firm and reliable. The bushing wear should meet the requirements, otherwise it should be replaced.

(4) Coat the bearing with butter and insert it into the stem nut. The disc springs are combined according to the requirements and reinstalled in turn. Finally, it is locked with a lock nut and then fixed firmly with screws.

2.3.1 The grinding qualified left and right valve discs are reinstalled on the valve stem clamp ring and fixed with upper and lower splints, and the universal top and adjusting gasket should be placed inside according to the maintenance situation.

2.3.2 Insert the valve stem together with the valve disc into the valve seat for test and inspection, and the valve disc and the valve seat sealing surface should be in contact with all the valve seat sealing surface to ensure that the valve disc sealing surface is higher than the valve seat sealing surface, and meet the quality requirements, otherwise the thickness of the universal top gasket should be adjusted until it is suitable, and sealed with a check gasket to prevent disconnection.

2.3.3 Clean the valve body, wipe the valve seat and valve disc. Then place the stem and disc into the seat and reinstall the bonnet.

2.3.4 Seal packing is added as required in the self-sealing part of the valve cover, the packing specifications and the number of turns should meet the quality standards, the upper part of the packing is pressed with a pressure ring, and finally closed with a cover plate.

2.3.5 The quadruple ring is assembled in turn, and the retaining ring is used to increase the anti-disconnection, and the nut of the valve cover lifting bolt is tightened.

2.3.6 Fill the packing material with the valve stem and seal the packing box as required, put it into the material gland and pressure plate, and check it tightly with hinge screws.

2.3.7 Assemble the bonnet frame, rotate the upper stem nut to make the frame fall on the valve body, and fasten it with connecting bolts to prevent it from falling off.

2.3.8 install a compound valve electric drive device; The top screw of the connection part should be tightened to prevent it from falling off, and the manual test is whether the door switch is flexible.

2.3.9 The valve sign is clear, intact and correct. The maintenance record is complete and clear; And the experience is qualified.

2.3.10 The insulation of pipelines and valves is complete, and the maintenance site is clean.    

3.1.1 The valve body should be free of defects such as sand holes, cracks and scouring, and should be dealt with in time after discovery.

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

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

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

3.2.2 The trapezoidal thread part of the valve stem should be intact, without defects such as broken buckle and bite buckle, and the amount of wear should not be greater than 1/3 of the trapezoidal thread thickness.

3.2.3 The surface is smooth and clean, no rust scale, and the sealing contact parts shall not have flake corrosion and surface delamination, and the uniform corrosion point depth ≥ more than 0.25 mm should be replaced. The finish should be guaranteed to be above ▽6.

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

3.2.5 After the combination of the cutting rod and the cutting rod nut, it should rotate flexibly, without jamming in the whole stroke, and the thread should be coated with lead powder lubrication protection.

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

3.3.2 The packing specifications should meet the size requirements of the sealed box, and should not be replaced by packing of too large or too small size, and the packing height should meet the requirements of the valve size, and should leave a thermal tight margin.

3.3.3 The packing interface should be cut into an oblique shape, the angle is 45 ° angle, the interface of each circle should be staggered by 90 °-180 °, the length of the cut packing should be appropriate, and there should be no gap or superposition at the interface in the packing box.

3.3.4 The packing seat and packing gland should be intact and free of rust and scale, the packing box should be clean and smooth, the gap between the door stem and the seat should be 0.1-0.3 mm, and the maximum should not exceed 0.5 mm, and the gap between the packing gland, the outer part of the seat ring and the inner wall of the packing box should be 0.2-0.3 mm, and the maximum should not exceed 0.5 mm.

3.3.5 After the hinge bolt is tightened, the pressing plate should be kept flat and the tightening force should be uniform. The packing gland and the inner hole of the pressure plate should be consistent with the gap around the valve stem. The packing gland should be pressed into the packing chamber at l/3 of its height size.

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

3.4.2 Assemble the test disc, and after the disc is inserted into the valve seat, ensure that the valve core is 5-7 mm higher than the valve seat to ensure that it is tightly closed.

3.4.3 When assembling the left and right valve discs, the self-adjustment should be flexible, and the anti-off device should be intact and reliable.

3.5.1 The internal bushing thread buckle should be in good condition, and there should be no broken buckle or random buckle, and the fixation with the shell should be reliable and no loosening.

3.5.2 The bearing parts should be in good condition and rotate flexibly. There are no defects such as cracks, rust and heavy skin on the surface of the inner and outer coat and steel balls.

3.5.3 The disc spring should be free of cracks and deformation, otherwise it should be replaced. 3.5.4 The surface fixing screws of the lock nut shall not be loose. The stem nut rotates flexibly and has an axial clearance of no more than 0.35 mm.