【Weekly Topic】What are the installation considerations for valves? ? (20110725--20110731)

General requirements for valve installation: (1) Valves should be installed in locations that are easily accessible and convenient for operation and maintenance. Valves on rows of pipes (such as those in inlet and outlet devices) should be arranged centrally, with consideration given to providing operation platforms and ladders. For valves on pipes arranged in parallel, their centerlines should be aligned as much as possible. The clear distance between the handwheels should not be less than 100 mm; to reduce the spacing between the pipes, the valves can be arranged offset from each other ； (2) The installation position of valves that are operated frequently should be convenient for operation, with the most suitable installation height being around 1.2 meters from the operating surface. When the height of the center of the valve handwheel exceeds 2 m above the operating surface, platforms shall be provided for centrally arranged valve groups, individually installed valves that are frequently operated, and safety valves. Appropriate measures (such as sprockets, extension rods, movable platforms, and portable ladders) shall also be taken for individually installed valves that are rarely operated. The chain of the sprocket should not obstruct passage. Valves on pipelines and equipment handling hazardous media must not be installed at a height level with a person’s head, so as to prevent head injuries or direct facial injuries in the event of valve leakage ； (3) The valves used for isolation equipment should be connected directly to the equipment’s pipe outlets or located near the equipment. Valves on the pipes connected to equipment that handles extremely hazardous or highly hazardous toxic substances should be connected directly to the equipment’s outlets, and such valves must not be operated using sprockets ； (4) Accident handling valves, such as valves for fire-fighting water and valves for fire-fighting steam, should be arranged dispersedly, taking into account safe operation during emergencies. Such valves should be installed behind the control room, behind the safety wall, outside the plant building, or in a location that provides a sufficient safety distance from the site of an accident, so that operators can operate them safely in the event of a fire ； (5) Unless the process has special requirements, valves on the pipelines at the bottom of equipment such as towers, reactors, and vertical vessels shall not be installed within the skirt ； (6) The isolation valve of the horizontal branch pipe leading off from the main pipe should be located on the horizontal section near its root ； (7) Lift check valves shall be installed on horizontal pipelines; vertical lift check valves shall be installed on vertical pipelines where the medium flows from bottom to top. Swing check valves should be installed preferentially in horizontal pipes; they can also be installed in vertical pipes where the medium flows from bottom to top ； The foot valve should be installed at the vertical pipe end of the centrifugal pump’s suction pipe ； To reduce the installation height of the pump outlet shut-off valve, a butterfly check valve can be used ； When the diameter of the pump outlet does not match that of the connected pipe, a reducing check valve can be used ； (8) The distance from the center of the handwheel of valves arranged around the operating platform to the edge of the platform should not exceed 450 mm. When the valve stem and handwheel extend above the platform and their height is less than 2 m, they must not impede the operator’s movements or passage ； (9) Valves for underground pipelines should be installed in pipe trenches or valve chambers; when necessary, valve extension rods should be provided. The fire water valve well should have clear markings ； (10) For valves on horizontal pipes, the direction of the valve stem can be determined in the following order: vertically upward ； Horizontal ； 45° upward tilt ； Incline downward at 45° ； It must not be directed vertically downward ； (11) For globe valves with horizontally installed valve stems, when the valve is open, the valve stem must not obstruct passage.

You need to understand the types and installation methods of ordinary valves, and also pay attention to the arrows on the valves, which indicate the flow direction. For special cases, please refer to the instructions

The installation location of a valve is determined by the type of valve and the actual conditions at the site. As for the stress exerted by a valve on the pipeline, I understand this to include not only the weight of the valve itself but also the impact force exerted by large pneumatic valves on the pipeline when they are opened or closed.

When installing valves, the following should be noted: a) Before installation, in addition to verifying the product certificate and test records, the valve model must be checked against the design requirements, and its installation direction must be determined based on the flow direction of the medium. b) Before installation, the valve should be cleaned and kept in a closed state. When installing and moving valves, the handwheel must not be used as a lifting point, nor should it be rotated arbitrarily. c) Stop valves, check valves, and throttle valves shall be installed correctly in accordance with the design specifications. When there are no flow direction indicators on the valve casing, the following principles shall be followed for determination: 1) Globe valves and check valves: The medium should flow upward from beneath the valve disc ； 2) Single-seat throttle valve: The medium flows from below the valve disc upward ； 3) Two-seat throttle valve: The side of the valve core that is visible in the closed state is the inlet side of the medium. d) All valves shall be connected naturally; forced fitting or external gravitational loads shall not be applied. The tension around the flange should be even to prevent damage to the valve due to additional stress. e) The installation of the valve actuation mechanism shall meet the following requirements: 1) The universal joint must rotate smoothly ； 2) The angle between the transmission rod and the valve stem axis should not exceed 300° ； 3) For valves with thermal displacement, their actuation mechanisms should incorporate compensating measures. f) For valve installation, the handwheel should not face downward, and it must be easy to operate and maintain. g) Valves with flange or threaded connections shall be installed closed. h) The connection of butt-welded valves to pipes should be carried out after heat treatment of the adjacent welds; TIG welding should be used for the root layer of the weld to ensure cleanliness inside. The valve should not be closed during welding to prevent overheating and deformation. The welding process shall comply with the relevant provisions of DL/T 869-2004 “Technical Regulations for Welding in Thermal Power Plants”. i) For imported valves, it is essential to refer to their installation instructions and carry out the installation in accordance with those requirements. For some valve models that are identical, but have valve tag numbers on them, it is necessary to check the tag numbers on the drawings in order to install them correctly.

After selecting the valve correctly, it must also be installed, maintained, and operated properly in order to fully utilize its efficiency. The quality of valve installation has a direct impact on its performance, so it must be given careful attention. The following points should be noted: 1. Direction and position. Many valves are directional, such as globe valves, throttle valves, pressure relief valves, check valves, etc. If installed in the wrong direction, it will affect their performance and lifespan (as in the case of throttle valves), or they may not function at all (as in the case of pressure relief valves), or it could even pose a danger (as in the case of check valves). For general valves, there are direction indicators on the valve body ； In the event that it is not present, it should be correctly identified based on the working principle of the valve. 2 Construction operations: Installation work must be carried out with care; avoid striking valves made of brittle materials. Before installation, the valve should be inspected to verify its specifications and model, and to check for any damage, especially to the valve stem. The debris inside the valve also needs to be removed. The valve should be tied to the flange when lifting it. The piping connected to the valve must be thoroughly cleaned. When installing threaded valves, the sealing packing should be wrapped around the pipe threads, not inside the valve, to prevent accumulation there and avoid affecting the flow of the medium. When installing flanged valves, be careful to tighten the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with an appropriate gap, to prevent excessive pressure on the valve and even cracking. Special attention should be paid to brittle materials and valves with low strength. For valves that need to be welded to pipes, spot welding should be performed first, followed by fully opening the closing element, and then performing a full weld. 3 For protective facilities, some valves also require external protection, namely insulation and heat retention. 4. For some valves in bypass lines and instrumentation, in addition to the necessary protective measures, bypass lines and instrumentation are also required. A bypass has been installed to facilitate the maintenance of the steam trap. Other valves also have bypasses for installation. Whether to install a bypass depends on the condition of the valve, its importance, and the requirements of production. 5 Replace the packing on the valves; some of the packing is no longer functional, and some is not suitable for the medium being used, so it is necessary to replace the packing.

Precautions for the installation and use of valves: 1. For high-temperature valves operating at temperatures above 200°C, since they are installed at room temperature, the temperature rises during normal operation, causing the bolts to expand due to heat and resulting in increased gaps. Therefore, it is necessary to tighten them again; this process is known as \"thermal tightening\". Operators must pay attention to this step, as failure to do so can lead to leaks. 2. When the weather is cold and the water valve remains closed for a long time, any accumulated water behind the valve should be drained. After the steam valve is closed, condensate must also be drained. At the bottom of the valve, there is a plug similar to a pipe plug; it can be opened to drain water. 3. Non-metallic valves: some are hard and brittle, while others have lower strength. When operating them, the force used for opening and closing should not be too great, especially forceful actions should be avoided. Be careful to prevent the object from being bumped. 4. When using a new valve, do not compress the packing too tightly – just enough to prevent leakage. This is to avoid excessive pressure on the valve stem, which could accelerate wear and make it difficult to open and close the valve. The quality of valve installation directly affects their performance; therefore, great care must be taken regarding the orientation and positioning of the valves, as well as valve installation work, protective measures for valves, bypasses and instruments, and the replacement of valve packing. (1) Direction and position: Many valves are directional, such as globe valves, throttle valves, pressure relief valves, check valves, etc. If installed in the wrong direction, it will affect their performance and lifespan (as in the case of throttle valves), or they may not function at all (as in the case of pressure relief valves), or it could even pose a danger (as in the case of check valves). For general valves, there are direction indicators on the valve body ； In the event that it is not present, it should be correctly identified based on the working principle of the valve. The valve chamber of the globe valve is asymmetrical on the left and right sides. The fluid must flow from bottom to top through the valve opening; this results in low fluid resistance (determined by its shape), easy operation when opening (due to the upward direction of the medium pressure), and no pressure exerted on the packing after closure, thus facilitating maintenance. This is why a stop valve must not be installed backwards. Other valves also have their own characteristics. The valve must be installed in a location that facilitates operation ； Even if installation is somewhat difficult temporarily, it’s important to consider the operators’ long-term work conditions. It is best for the valve handwheel to be at chest level (generally 1 above the operating floor). 2 meters), which makes it easier to open and close the valve. The handwheel of the floor valve should face upward and not be tilted, to avoid awkward operation. For wall-mounted units, space must also be left next to the device’s valves for the operator to stand. It is necessary to avoid working with the head raised, especially when dealing with acids, bases, toxic substances, etc., as it is very unsafe. The gate valve should not be installed upside down (with the handwheel facing downward), as this will cause the medium to remain in the space above the valve cover for an extended period, leading to corrosion of the valve stem; it is also prohibited by certain process requirements. It is also very inconvenient to replace the packing at the same time. Straight-through gate valves should not be installed underground, as moisture can cause corrosion of the exposed valve stem. For lift-type check valves, it is necessary to ensure that their valve discs are vertical during installation, so as to allow for smooth lifting and lowering. For swing check valves, it is necessary to ensure that their pin shafts are horizontal during installation, so as to allow for smooth swinging. The pressure relief valve must be installed vertically on a horizontal pipe, without any tilt in any direction. (II) Care must be taken during the installation of valves; it is essential to avoid impacting valves made of brittle materials. Before installation, the valve should be inspected to verify its specifications and model, and to check for any damage, especially to the valve stem. It needs to be turned a few more times to check if it is skewed, as the valve stem is most likely to become misaligned during transportation. The debris inside the valve also needs to be removed. When lifting the valve, do not tie the rope to the handwheel or valve stem, as this may damage those components; instead, it should be tied to the flange. The pipeline connected to the valve must be thoroughly cleaned. Compressed air can be used to blow away iron oxide filings, sediment, slag, and other debris. These debris not only easily scratch the sealing surfaces of the valves, but large particles of debris (such as weld slag) can also block small valves, rendering them ineffective. When installing threaded valves, the sealing filler (flax mixed with lead grease or PTFE tape) should be wrapped around the pipe threads, avoiding contact with the inside of the valve, so as to prevent accumulation there and interference with the flow of the medium. When installing flanged valves, be careful to tighten the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with an appropriate gap, to prevent excessive pressure on the valve and even cracking. Special attention should be paid to brittle materials and valves with low strength. For valves that need to be welded to pipes, spot welding should be performed first, followed by fully opening the closing element, and then performing a full weld. (III) Valve protection facilities: Some valves also require external protection facilities, namely insulation and heat retention. Heating steam pipelines are sometimes also added inside the insulation layer. It depends on the production requirements to determine which types of valves should be insulated or kept cold. In principle, whenever the temperature of the medium inside the valve drops too much, it can affect production efficiency or cause the valve to be damaged by freezing; in such cases, insulation, or even heating, is necessary ； When valves are exposed, which is detrimental to production or can cause problems such as frosting, insulation is required. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc ； Insulation materials include cork, perlite, foam, plastic, etc. Water and steam valves that have not been used for a long time must have any accumulated water drained. (IV) For some valves in the bypass and instrumentation systems, in addition to the necessary protective devices, bypasses and instrumentation are also required. A bypass has been installed to facilitate the maintenance of the steam trap. Other valves also have bypasses for installation. Whether to install a bypass depends on the condition of the valve, its importance, and the requirements of production. (5) Replace the packing in the valves; some of the packing is no longer functional, and some is not suitable for the medium being used, so it is necessary to replace the packing. Valve manufacturers cannot take into account the wide variety of different media used by end-users; ordinary packing is always installed in the stuffing box, but it is necessary to ensure that the packing is suitable for the specific medium being used. When replacing the packing, press it in circle by circle. The seams between each loop should be at a 45-degree angle, with the seams between loops offset by 180 degrees. The packing height must take into account the amount of additional compression that the gland can apply. At the same time, it is necessary to allow the lower part of the gland to compress the packing chamber to an appropriate depth; this depth is generally 10-20% of the total depth of the packing chamber. For high-demand valves, the joint angle is 30 degrees. The seams between the circles are offset by 120 degrees. In addition to the fillers mentioned above, shaped fillers such as rubber O-rings (natural rubber is resistant to weak alkalis at temperatures below 60 degrees Celsius, nitrile rubber is resistant to oils at temperatures below 80 degrees Celsius, and fluororubber is resistant to various corrosive agents at temperatures below 150 degrees Celsius), triple-layered polytetrafluoroethylene rings (resistant to highly corrosive agents at temperatures below 200 degrees Celsius), and nylon bowl-shaped rings (resistant to ammonia and alkalis at temperatures below 120 degrees Celsius) can also be used depending on the specific circumstances. Wrapping a layer of PTFE tape around the ordinary asbestos packing can improve the sealing effect and reduce the electrochemical corrosion of the valve stem. When compressing the packing, turn the valve stem at the same time to ensure even compression throughout and to prevent it from being too tight; apply even force when tightening the gland, without tilting it.

While meeting the installation requirements for the valves, the actual site location should be taken into consideration as much as possible to facilitate operation and maintenance, as well as to avoid obstacles in the passageways. For high- and low-temperature valves, it is important to ensure proper insulation to prevent heat or cold loss, as well as to avoid any risk of injury to personnel.

The installation location of valves that are used frequently should be convenient for operation; the optimal installation height is around 1.2 meters above or below the operating surface. Thank you