I would like to ask the experts: Can the valve stem nut of a gate valve be replaced while the valve is still in operation?
Thread Content
The medium flowing through the pipeline is crude oil, and the operating pressure is around 16 kilograms. At present, the nut on the valve stem of the gate valve has broken (the copper sleeve), resulting in the valve being able to open only but not to close. I was wondering if it’s possible to replace it online? Is it still necessary to relieve pressure from the pipeline before replacing it?
The fixing pin on the valve wheel is damaged and can be replaced. Any area that is not under pressure can be treated; if in doubt, seek guidance from a professional.
Generally, during design, a upper sealing mechanism is incorporated into the valve stem of gate valves to prevent it from flying out. In emergency situations, it is possible to replace the packing while the valve is still under pressure (the valve must first be fully opened so that the upper sealing pair can provide a seal); however, replacing the packing under pressure is generally not allowed. There are also some manufacturers who design gate valves and globe valves without such a mechanism to prevent the stem from flying out. In your case, since the copper nut was removed and the stem did not fly out during operation, it can be assumed that there is a mechanism in place to prevent the stem from flying out. You can proceed with replacing the packing directly, without the need to relieve pressure in the pipeline – simply install a new copper nut that fits properly. It seems that the valve stem nut in the picture is rusted; it doesn’t appear to be made of copper alloy. With such rust and a lack of lubrication, operating the valve should be quite difficult. Furthermore, if it is necessary to replace the packing while the valve is under pressure, for safety reasons it is essential to first confirm with the manufacturer whether the valve has an upper sealing mechanism to prevent it from flying out; otherwise, a valve lacking such a mechanism could be pushed out by the medium, leading to accidents such as injuries or deaths.
If a matching copper sleeve is used for connection, it will close properly; ask the manufacturer whether it can be repaired. If that doesn’t work, pressure relief is the only option; the valve located ahead of the pipeline needs to be closed and then replaced.
This post was last edited by xlxuiin on 2021-11-13 21:35. It’s okay. Generally, the handwheel bracket and the valve cover are separate; if they are integrated, they cannot be replaced online and pressure must first be released.
What is the sealing structure on the valve stem of gate valves to prevent it from flying out? https://bbs.hcbbs.com/thread-3271051-1-1.html (Source: Haichuan Chemical Industry Forum)
Judging from the handwheel, the valve must be quite large – how much force did you use to operate it? lol. When such a large valve is closed, be sure to reset it; as for how to do this, the poster should consult the manufacturer, after all, it’s a Class A/B system.