For soft-sealed gate valves, the connection between the valve stem and the valve core fails due to corrosion, wear or improper operation during the opening and closing of the valve. The valve core will fall off every year. After the valve is closed, it cannot be opened, and it can only be replaced after being cut out from the system; if it cannot be cut out from the system, only another process or device shutdown is required.

1. Repair method

When the valve core falls off and cannot be cut out, the valve body, valve core and valve seat can be changed under the condition that the sealing medium is sealed, and the valve cover, valve stem, copper sleeve, packing and gland can be changed. After the assembly method, the valve core is exposed, and then the valve stem and the valve core are restored by the conventional method, so that the three parts of the valve can be continuously sealed and the valve can be opened again. After the bonnet is disassembled, except for special valves, the wedge angle of the valve core is within the friction angle range. No matter how the pressure on the two ends of the valve core changes, the valve core will not squeeze out of the valve seat by itself under the self-locking condition. For the valve core, there is no squeeze out.

2. Operation steps

1) Take the rising stem wedge gate valve as an example. When the connection between the valve stem and the valve core fails, the handwheel can still be rotated. The valve core can be pushed back to the seat through the handwheel to ensure the sealing surface between the valve core and the valve seat This is a prerequisite for applying this repair method. First unscrew the valve packing gland nut, loosen the packing, and then loosen the nuts on all the bolts on the valve cover a few times, but not completely unscrewing it yet.

2) Continue to turn the handwheel in the closed direction. At this time, the valve stem will no longer move, but the whole part above the valve cover is separated from the valve body. This operation is to observe whether the seal between the valve core and the valve seat is sealed. Seal, if the sealing is not tight and there is medium leakage, as long as the amount is not large, the on-site construction processing will not be affected in a short time, you can completely unscrew all the nuts on the bolts, and remove the upper part of the valve cover and the valve stem , Expose the top of the valve core in the valve seat, check the original connection method of the valve stem and the valve core, and the reason for the failure, and develop solutions.

3) Gently rotate the valve stem in the upper part of the bonnet to withdraw from the stem nut and stuffing box. At the same time, unscrew the lock nut of the stem nut and remove the handwheel and stem nut. It can rotate freely without limit.

4) Reconnect the removed valve stem with the valve core separately. Generally, the valve stem and the valve core are restored by welding. This method is well applied to the water line, wind line and steam line where the valve core is easy to fall off. Above, even if the valve core valve seat is not tightly sealed and there is medium leakage, it can be used as long as it does not affect the construction. When repairing oil and gas medium valves, it is not safe to weld directly. The end of the valve stem can be taken out and processed into the required special form. The connection contact surface of the valve stem and the valve core is bonded with high strength during installation. Healing agent treatment, or on-site drilling and tapping on the top of the valve core, additional threads on the connecting end of the valve stem, and then connecting. It should be noted that after the valve stem and the valve core are reconnected and installed, the installation plane of the valve stem and the valve cover should be vertical, and the neutrality should be good. Otherwise, when the valve is opened after repair, the valve stem will bend and it will be difficult to switch.

5) After the valve stem is connected, put the valve cover, part of the packing and gland, and the valve stem nut on the valve stem in turn, and the sealing gasket can be replaced according to the situation to prevent leakage after the sealing surface is put into use. After the valve cover is in place, align the screw holes of the valve body and tighten the bolts symmetrically. If necessary, add part of the packing to the stuffing box, and press the packing gland properly. Finally, put the stem nut on the handwheel and tighten the lock nut. The repair work is over.