- Remove the fixing bolts of the upper frame of the bonnet; unscrew the nuts of the four bolts on the bonnet and turn the stem nut counterclockwise to separate the valve frame from the valve body. Then use a lifting tool to lift the frame down to the right place. The stem nut is to be disassembled for inspection.
- Take out the retainer ring at the sealing part of the valve body, and press the bonnet with a special tool to make a gap between the bonnet and quadruple ring. Then take out the sealing ring containing four parts one by one. Finally, use a lifting tool to lift the valve body by the valve bonnet together with the valve stem and valve disc. Put it on the maintenance site, and pay attention to prevent damage to the joint surface of valve discs.
- Clean the inside of the valve body; check the joint surface of the valve seat, and determine the maintenance method. Cover the disassembled valve with a special cover plate or cover, and seal it.
- Loosen the hinge bolts of the packing box on the valve bonnet. Loosen the packing gland and unscrew the valve stem.
- Remove the upper and lower splints of the disc frame. Take out the left and right discs, and keep the internal universal top and gasket well. Measure the total thickness of the gasket and make a record.
2. Repair of various parts of gate valves
- The joint surface of the gate valve seat should be ground with a special grinding tool, for example, a grinding gun. Abrasive sand or sandcloth can be used for grinding. The sandcloth with a rough surface should be adopted and then a smooth surface. Finally, polishing should be adopted.
- The joint surface of the valve disc can be ground by hand or a grinding machine. If the surface has a deep pit or groove, it can be sent to a lathe or grinder for slightly processing, and it should be polished after it is flat.
- Clean the bonnet and sealing packing. Remove the rust and dirt on the inner and outer walls of the packing pressing ring, so that the pressing ring can be smoothly inserted into the upper part of the bonnet, which is convenient for pressing the sealing packing.
- Clean the inner packing of the packing box of the valve stem. Check whether the inner packing seat ring is intact. The gap between the inner hole and stem should meet the requirements, and the outer ring and the inner wall of the packing box should not be jammed.
- Clean the rust on the packing gland and pressing plate, and the surface should be clean and intact. The gap between the inner hole of the gland and the stem should meet the requirements, and the outer wall and packing box should be free from jams. Otherwise, repairs should be carried out.
- Loosen the hinge bolts. Check whether the threaded part and nut are intact. Sightly screw the root of the bolt by hand, and the pin can rotate flexibly.
- Clean up the rust on the surface of the valve stem; check whether or not the stem bends, and straighten it if necessary. The trapezoidal thread part should be intact, no breakage and damage, and be applied with lead powder after cleaning.
- Clean the ring made up of four parts and the surface should be smooth. The plane must not have burrs or curling edges.
- All fastening bolts should be cleaned; the nuts should be complete and flexible, and the threaded parts should be coated with lead powder.
3. Cleaning the stem nut and internal bearing
① Remove the fixing screw between lock nuts of stem nuts and housings, and unscrew the lock screw in a counterclockwise direction.
② Take out the stem nut and bearing, disc spring, and clean them with kerosene. Check whether the bearing rotates flexibly and the disc spring has cracks.
③ Clean the valve stem nut; check whether the inner bushing trapezoidal screw is intact, and the fixing screw for the shell should be firm and reliable. The wear of the bushing should meet the requirements. Otherwise, it should be replaced.
④ Coat the bearing with grease. Disc springs are assembled based on requirements in sequence. Finally, tighten it with a lock nut, and then fix it firmly with a screw.
4. Assembly of gate valves
① Remove the fixing screw between lock nuts of stem nuts and housings, and unscrew the lock screw in a counterclockwise direction.
② Take out the stem nut and bearing, disc spring, and clean them with kerosene. Check whether the bearing rotates flexibly and the disc spring has cracks.
③ Clean the valve stem nut; check whether the inner bushing trapezoidal screw is intact, and the fixing screw for the shell should be firm and reliable. The wear of the bushing should meet the requirements. Otherwise, it should be replaced.
④ Coat the bearing with grease. Disc springs are assembled based on requirements in sequence. Finally, tighten it with a lock nut, and then fix it firmly with a screw.
4. Assembly of gate valves
- Put the qualified left and right discs on the clamp ring of the stem and fix them with the upper and lower clamps.
- Insert the valve stem together with the valve disc into the valve seat for test inspection. After the valve disc and sealing surface of the valve seat are in full contact, it should be ensured that the sealing surface of the valve disc is higher than that of the valve seat and meets the quality requirements. Otherwise, the thickness of the gasket at the top should be adjusted, and the retainer gasket is used to seal and prevent it from falling off.
- Clean the valve body, valve seat and disc. Then put the valve stem along with valve disc in the valve seat, and install the valve bonnet.
- Install sealing packing as required on the self-sealing part of the bonnet. The packing specification and number of turns should meet the standard. The upper part of the packing is pressed tightly with a pressing ring and finally closed with a cover plate.
- Assemble four parts of rings in sequence. Use a retaining ring to prevent it from falling off; tighten the valve bonnet and raise the nut of the bolt.
- Fill the sealing packing box of the valve stem with the packing as required; insert the packing gland and pressing plate, and tighten with a hinge screw.
- 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.
- Assemble the valve's electric drive device; the top wire of the connection part should be tightened to prevent falling off, and manually check whether the opening and closing buttons are flexible.
- The valve's nameplate should be clear, intact, and correct. The repair records are complete and clear with acceptance.
- The pipelines and valves have complete insulation, and the maintenance site should be cleaned.
Next: Maintenance and Quality Standards of Gate Valves
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