Wenzhou Unique Valve Co., Ltd.
Points for Attention for Disassembly of Valves
Apr 26, 2021
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Installation of valves can be used as a criteria for general matters needing attention for disassembly of valves. However, confirm that there is no pressure inside the pipeline and valve, or replace the medium with inert gas before disassembling.
Disassembly of valves with flange connections
Disassembly of valves with flange connections
- In principle, bolts should be removed with a wrench.
- In order to protect the sealing surface of the valve flange, you can remove the flange piping on both sides before disassembling the valve according to the situation.
Disassembly of welded valves
- When gas cutting is used, it is necessary to cut at the position of the welding seam.
- After cutting, the cutting residue inside the pipe and the valve should be removed.
Reinstallation of valves
Directions and locations
Many valves are directional, such as globe valves, throttle valves, pressure reducing valves, check valves, etc. If they are installed reversely, their use effect and service life will be affected, for example, throttle valves; some will not work at all like pressure reducing valves, or even cause danger, for example, check valves. Generally, there are directional signs on the valve body; if not, they should be correctly identified according to the working principle of the valve. The valve cavity of the globe valve is asymmetrical, and the fluid should pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape). The opening is labor-saving, because the medium pressure is upward, and the medium does not press the packing after closing, which is convenient for maintenance. This is the reason why the globe valve cannot be installed reversely. Other valves also have their own characteristics.
The location of the valve's installation must be convenient for operation; even if the installation is temporarily difficult, it is necessary to consider the long-term maintenance for the operator. It is best to keep the valve handwheel align with the chest, which is usually 1.2 meters away from the operating floor and is easier to open and close the valve. Valves that are close to walls or equipment should reserve some space for an operator to stand.
Do not install the gate valve upside down, that is, the handwheel is downward. Otherwise, the medium will remain in the valve bonnet for a long time, which will easily corrode the valve stem. It is also forbidden in certain process requirements. Meanwhile, it is extremely inconvenient to replace the packing. Gate valves with rising stems should not be installed underground, or the exposed stem will be corroded because of moisture.
When installing the lift check valve, make sure that its valve disc is vertical so that it can be lifted and moved flexibly. For swing check valves, ensure that their pin shafts are horizontal when they are installed so that they can swing flexibly.
The pressure reducing valve should be installed vertical on a horizontal pipe, and it should not be tilted in all directions.
Construction
The operators must be careful with the installation. Valves in brittle materials must not be hit. Before installation, check the valve well; check the specifications, and identify whether there is any damage, especially the valve stem. Rotate it a few times to see if it is skewed, because the valve stem is most likely to be skewed during transportation. Also, remove the debris in the valve. When the valve is hoisted, the rope should not be tied to the handwheel or valve stem to avoid damaging these parts. It should be tied to the flange. The pipeline connected to the valve must be cleaned. Compressed air can be used to blow iron oxide filings, mud sand, welding slags and other debris. These debris are not only easy to scratch the sealing surface of the valve, the large particles of debris such as welding slags can also block the small valve and make it not work.
When installing valves with threaded ends, the packing should be wrapped on the pipe thread, and do not let the packing get into the valve so as to avoid the accumulation in the valve, affecting the flow of the medium.
When installing valves with flange connections, pay attention to tighten the bolts symmetrically and evenly. The valve flange and pipe flange must be parallel with reasonable clearance to avoid excessive pressure or even cracking of the valve. Special attention should be paid to valves that are in brittle materials and whose strength is low. Valves that need to be welded to the pipe should be spot welded first, then the closing part should be fully opened, and then welded them well.
Protective facilities
Some valves also need external protection, which is heat preservation and cold preservation. Sometimes heat tracing steam lines are added in the insulation layer. What kind of valve should be kept warm or cold depending on the production requirements. In principle, if the temperature reduces too much for the medium in the valve, it will affect production efficiency or freeze the valve, then heat preservation or even hear tracing is required. Cold preservation is needed for exposed valves which are unfavorable to production or cause frost and other undesirable phenomena. Materials used for heat preservation are asbestos, slag wool, glass wool, perlite, diatomite, vermiculite, etc. Materials used for cold preservation include cork wood, perlite, foam and plastics. Stagnant water in the water and steam valves that have not been used for a long time must be drained.
Bypasses and instruments
In addition to the necessary protection facilities, some valves also have bypasses and instruments. A bypass is installed to facilitate the maintenance of the steam trap. Whether to install the bypass depends on the valve's condition, importance and production requirements.
Replacement of packing
For valves in stock, some packing is no longer good, or some do not match the medium, which require replacement of packing. The valve manufacturer cannot consider various types of media. The stuffing box is always filled with ordinary packing, but when the packing is used, it must be compatible with the medium.
Directions and locations
Many valves are directional, such as globe valves, throttle valves, pressure reducing valves, check valves, etc. If they are installed reversely, their use effect and service life will be affected, for example, throttle valves; some will not work at all like pressure reducing valves, or even cause danger, for example, check valves. Generally, there are directional signs on the valve body; if not, they should be correctly identified according to the working principle of the valve. The valve cavity of the globe valve is asymmetrical, and the fluid should pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape). The opening is labor-saving, because the medium pressure is upward, and the medium does not press the packing after closing, which is convenient for maintenance. This is the reason why the globe valve cannot be installed reversely. Other valves also have their own characteristics.
The location of the valve's installation must be convenient for operation; even if the installation is temporarily difficult, it is necessary to consider the long-term maintenance for the operator. It is best to keep the valve handwheel align with the chest, which is usually 1.2 meters away from the operating floor and is easier to open and close the valve. Valves that are close to walls or equipment should reserve some space for an operator to stand.
Do not install the gate valve upside down, that is, the handwheel is downward. Otherwise, the medium will remain in the valve bonnet for a long time, which will easily corrode the valve stem. It is also forbidden in certain process requirements. Meanwhile, it is extremely inconvenient to replace the packing. Gate valves with rising stems should not be installed underground, or the exposed stem will be corroded because of moisture.
When installing the lift check valve, make sure that its valve disc is vertical so that it can be lifted and moved flexibly. For swing check valves, ensure that their pin shafts are horizontal when they are installed so that they can swing flexibly.
The pressure reducing valve should be installed vertical on a horizontal pipe, and it should not be tilted in all directions.
Construction
The operators must be careful with the installation. Valves in brittle materials must not be hit. Before installation, check the valve well; check the specifications, and identify whether there is any damage, especially the valve stem. Rotate it a few times to see if it is skewed, because the valve stem is most likely to be skewed during transportation. Also, remove the debris in the valve. When the valve is hoisted, the rope should not be tied to the handwheel or valve stem to avoid damaging these parts. It should be tied to the flange. The pipeline connected to the valve must be cleaned. Compressed air can be used to blow iron oxide filings, mud sand, welding slags and other debris. These debris are not only easy to scratch the sealing surface of the valve, the large particles of debris such as welding slags can also block the small valve and make it not work.
When installing valves with threaded ends, the packing should be wrapped on the pipe thread, and do not let the packing get into the valve so as to avoid the accumulation in the valve, affecting the flow of the medium.
When installing valves with flange connections, pay attention to tighten the bolts symmetrically and evenly. The valve flange and pipe flange must be parallel with reasonable clearance to avoid excessive pressure or even cracking of the valve. Special attention should be paid to valves that are in brittle materials and whose strength is low. Valves that need to be welded to the pipe should be spot welded first, then the closing part should be fully opened, and then welded them well.
Protective facilitiesSome valves also need external protection, which is heat preservation and cold preservation. Sometimes heat tracing steam lines are added in the insulation layer. What kind of valve should be kept warm or cold depending on the production requirements. In principle, if the temperature reduces too much for the medium in the valve, it will affect production efficiency or freeze the valve, then heat preservation or even hear tracing is required. Cold preservation is needed for exposed valves which are unfavorable to production or cause frost and other undesirable phenomena. Materials used for heat preservation are asbestos, slag wool, glass wool, perlite, diatomite, vermiculite, etc. Materials used for cold preservation include cork wood, perlite, foam and plastics. Stagnant water in the water and steam valves that have not been used for a long time must be drained.
Bypasses and instruments
In addition to the necessary protection facilities, some valves also have bypasses and instruments. A bypass is installed to facilitate the maintenance of the steam trap. Whether to install the bypass depends on the valve's condition, importance and production requirements.
Replacement of packing
For valves in stock, some packing is no longer good, or some do not match the medium, which require replacement of packing. The valve manufacturer cannot consider various types of media. The stuffing box is always filled with ordinary packing, but when the packing is used, it must be compatible with the medium.
