After the valve plate of the gate valve falls off, it should be repaired
For the rising stem wedge gate valve, 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, and the valve core falls off every year. After the valve is closed, it cannot be opened. 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. To
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 it has been sealed by the medium, 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 reopened. After the bonnet is disassembled, except for special valves, the wedge angle of the valve core is within the friction angle region. No matter how the pressure on the two ends of the valve core changes, the valve core will not be squeezed 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 valve seat through the handwheel to ensure the two sealing surfaces of the valve core and the valve seat. This is the prerequisite for the application of 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 closing 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 the seal between the valve core and the two sealing surfaces of the valve seat. Whether it is sealed or not, if the sealing is not tight and there is medium leakage, as long as the amount is not large, and the on-site construction process will not be affected in a short time, all the nuts on the bolts can be completely unscrewed, and the upper part of the valve cover and the valve can be removed. Exposed 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 formulate 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 connection between the valve stem and the valve core is restored by welding. This method is well applied to the water line, wind line and steam where the valve core is easy to fall off. Online, even if the valve core and valve seat are 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 first and then 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, and matching 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, the valve stem will bend and the switch will be difficult when the valve is opened after the repair.
(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 screw in. The sealing gasket may 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.
This method does not need to cut out of the system and repair it online. When repairing, 2 to 3 people will operate, and the work can be completed within 1.5 hours. The cost is mainly for the construction and material costs of disassembly, welding, bonding or drilling, generally 200 to 1,000 yuan. After the repair, the valve switch is normal.
3. Examples
The steam-stabilizing cooler (cold 304/1.2) cooling water inlet valve (DN150) and the fractionation tower top cooler (cold 202/1.2) cooling water inlet valve (DN200) of the catalytic device were found to have fallen off the valve core after the installation was started. The two valves were repaired in a short period of time by the above method, and the loss of production shutdown was avoided. The two applications alone have directly reduced the loss by 30,000 yuan and indirectly recovered the loss by 180,000 yuan. These valves have been in good operating condition until now, and they are still opening and closing normally, which proves the feasibility of the above-mentioned repair methods.