Repair after Core Falling off
For rising stem wedge gate valve, connection between stem and core loses efficacy which caused by corrosion, abrasion or improper operation during valve on-off, then, the core falls off. If the valve cannot be opened after being closed, the valve only can be cut out from the system and replaced. If the valve cannot be cut out from the system, it should be connected with other fluid system or stopped.
When the core falls off while cannot be cut out, change the assemble method of bonnet, stem, cooper bush and expose core, under the situation that the media having been sealed. Then, recover the connection between stem and core, so that can ensure three sealing on valve and open the valve again. After disassembling the bonnet, wedge angle of core is in friction area. No matter how change the pressure on two ends of core is, the core cannot be squeezed out from the seat by itself under self-locking.
2. Operating sequence
(1) When the connection between stem and core loses efficacy while the hand wheel still can be rotated, push the core back to seat through hand wheel, maintaining the sealing between core and seat. It is the precondition that using the repairing method. Firstly, screw gland nut and loose packing. Then unscrew all of nuts on bonnet while do not unscrew them completely.
(2) Continue rotating hand wheel to the direction of closing. Then, stem does not move any more while total part on bonnet relatively separate from the body. The operation is used observe whether the sealing between core and seat is realized or not. If the sealing is not rigorous and the media leak out, it cannot influence site operation in short time with less leakage. Then unscrew all of nuts completely and take down the top part on bonnet and stem. Expose the top of core on seat. Check the original connection between stem and core and failure cause. Formulate solution.
(3) Gently rotate the stem in top part of bonnet. Retreat it from nut of stem and packing. Meanwhile, nuts of stem and locknuts also should be unscrewed. Take down hand wheel and nuts of stem.
(4) Reconnect the stem with core solely. In general, the reconnection between stem and core usually adopts welding. The method is quit suitable for waterline, wind line and steam line where core easily falls off. For oil or gas media, is dangerous for directly welding. Firstly, take out tip of stem and then, process into required special form. The contact surface between stem and core can be dealt with by using high strength adhesive during installation. Also can drill on the top of core. The connection end of stem can be added with other matched treads, then, connect them. What should be noticed that stem should be vertical with bonnet after connecting stem and core.
(5) After connecting stem, put bonnet, part of packing and gland, nuts of stem on stem successively and screw them. Sealing gasket can be replaced based on situation, in case of leakage after sealing face coming into use. After bonnet in place, symmetrically tighten bolts, aiming at screw holes of body. Compress gland of packing properly. Lastly, put nuts of stem on hand wheel and tighten nuts. The repairing is finished.
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