After selecting the valve correctly, it’s also crucial to install, maintain, and operate it properly in order to fully harness its performance.

　　Section 1: Installation: The quality of valve installation directly affects its performance, so it must be carefully attended to.

　　1) Direction and Position

　　If installed in the wrong direction, it can affect performance and service life—for example, with a throttling valve—or render the valve completely ineffective—for example, with a pressure-reducing valve—or even pose a safety hazard—for example, with a check valve. In most cases, valves will have directional markings on their bodies; if no such markings are present, you should correctly identify the correct flow direction based on the valve’s operating principle.

　　The valve cavity of a globe valve is asymmetric left and right. To minimize fluid resistance (determined by its shape), the fluid must flow upward through the valve port from bottom to top. This design also makes it easier to open (since the medium pressure acts upward) and prevents the medium from pressing against the packing when the valve is closed, thus facilitating maintenance. That’s precisely why a globe valve must not be installed backward. Other types of valves each have their own unique characteristics as well.

　　The installation location of valves must be convenient for operation. Even if initial installation is somewhat challenging, it’s important to consider the long-term convenience of operators. Ideally, the valve handwheel should be at chest level (typically about 1.2 meters above the operating floor), making it easier and less strenuous to open and close the valve. For floor-mounted valves, the handwheel should face upward rather than tilting, to prevent awkward or uncomfortable operation. For valves located against walls or near equipment, sufficient standing space for operators must be provided. Avoid operating valves while looking upward—especially when handling corrosive, alkaline, or toxic media—otherwise, it could pose serious safety risks.

　　Do not install the gate valve upside down (i.e., with the handwheel facing downward), as this could cause the medium to remain trapped in the valve bonnet space for extended periods, easily leading to corrosion of the valve stem and violating certain process requirements. Additionally, replacing the packing would become extremely inconvenient.

　　Do not install rising stem gate valves underground; otherwise, the exposed valve stem will corrode due to moisture.

　　For lift-type check valves, ensure that the valve disc is installed vertically during installation to allow for smooth lifting and lowering.

　　For swing check valves, ensure that the pin shaft is horizontal during installation to allow for smooth and flexible swinging motion.

　　The pressure relief valve must be installed vertically on a horizontal pipe, with no inclination in any direction.

　　Valve installation work

　　Installation and construction must be carried out with care; avoid any impact on valves made of brittle materials.

　　Before installation, the valve should be inspected to verify its specifications and model number and to check for any damage—especially to the valve stem. Also, turn the valve several times to see whether it is bent or skewed, as the valve stem is most likely to become bent during transportation. Additionally, remove any debris from inside the valve.

　　When lifting the valve, do not tie the rope to the handwheel or valve stem, as this could damage these components. Instead, tie the rope to the flange.

　　The pipelines connected to the valve must be thoroughly cleaned. Compressed air can be used to blow away iron oxide chips, silt, welding slag, and other debris. Such debris not only easily scratches the sealing surfaces of the valve but can also clog small valves with larger particles (such as welding slag), rendering them inoperable.

　　When installing screw-type valves, wrap the sealing packing (such as hemp fiber with lead oil or PTFE raw tape) around the pipe threads, but be careful not to let any of it get inside the valve, as accumulation inside the valve could impede the flow of the medium.

　　When installing flanged valves, be sure 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, which could even cause it to crack. This is especially important for valves made of brittle materials or those with low strength.

　　Valves that need to be welded to pipes should first be tack-welded, then the closure member should be fully opened, and finally welded shut.

　　Valve protection devices

　　Some valves also require external protection—namely, thermal insulation and cryogenic insulation. Sometimes, heating steam lines are even installed within the insulation layer. Which valves should be insulated or cryogenically insulated depends on the specific production requirements. As a general rule, any valve whose internal medium experiences excessive temperature reduction and thereby affects production efficiency or risks freezing the valve itself must be thermally insulated—and may even require auxiliary heating. Conversely, any valve that is exposed and adversely affects production or causes undesirable phenomena such as frost formation must be cryogenically insulated. Thermal insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, and vermiculite; cryogenic insulation materials include cork, perlite, foam, and plastics. Water and steam valves that are not used for extended periods must have any accumulated water drained completely.

　　Valve bypass and instrumentation

　　Some valves, in addition to the necessary protective devices, should also be equipped with bypass lines and instrumentation. The installation of a bypass facilitates maintenance and inspection of the drain valve. Other valves may also be fitted with bypass lines. Whether or not to install a bypass depends on the condition of the valve, its importance, and the requirements of the production process.

　　Valve packing replacement

　　Some of the valves in stock have packing that’s no longer effective, while others are incompatible with the medium being used—this necessitates replacing the packing.

　　Valve manufacturers cannot account for the wide variety of media used by different end users. Therefore, standard packing rings are always installed in the stuffing box; however, during actual use, the packing must be compatible with the medium being handled.

　　When replacing the packing, it should be pressed in layer by layer. The joints between each layer should ideally be at a 45-degree angle, and the joints of adjacent layers should be staggered by 180 degrees. The height of the packing should allow sufficient room for the gland follower to continue tightening; at the same time, the lower part of the gland follower should press the packing chamber to an appropriate depth, typically ranging from 10% to 20% of the total depth of the packing chamber.

　　For valves with high requirements, the joint angle is 30 degrees. The joints between adjacent rings are staggered by 120 degrees.

　　In addition to the packing materials mentioned above, depending on specific conditions, you can also use rubber O-rings (natural rubber is suitable for weak alkaline environments below 60°C; nitrile rubber is suitable for oils below 80°C; fluororubber is resistant to a variety of corrosive media below 150°C), three-layer stacked PTFE rings (suitable for strong corrosive media below 200°C), and nylon bowl-shaped rings (suitable for ammonia and alkalis below 120°C) as molded packing materials. Furthermore, wrapping a layer of PTFE raw tape around the exterior of conventional asbestos packing can enhance the sealing performance and reduce electrochemical corrosion of the valve stem.

　　When tightening the packing, rotate the valve stem simultaneously to ensure even pressure around the circumference and prevent it from becoming too tight. Tighten the gland nut with even force, avoiding any tilting.