1. Direction and Position

　　Many valves are directional.

　　For example, shut-off valves, throttling valves, pressure-reducing valves, and check valves: if installed in the wrong orientation, their performance and service life may be compromised (as with throttling valves), they may fail to function altogether (as with pressure-reducing valves), or even pose safety hazards (as with check valves). In general, valves are marked with directional indicators on the valve body; if no such markings are present, the correct orientation should be determined based on the valve’s operating principle.

　　The valve body of a globe valve is asymmetrical left and right; fluid must flow upward through the valve port, which minimizes flow resistance (due to the valve’s design) and makes it easier to open (because the medium pressure acts upward). After closure, the medium does not press against the packing, facilitating maintenance. This is why a globe valve must never be installed in reverse. Other types of valves also have their own specific characteristics.

　　The valve installation location must be convenient for operation.

　　Even if installation is temporarily more challenging, it should be carried out with the long-term convenience of operators in mind. Ideally, the valve handwheel should be aligned with the operator’s chest—typically about 1.2 meters above the operating floor—so that opening and closing the valve requires less effort. For floor-mounted valves, the handwheel should face upward and not be tilted, to prevent awkward or strained operation. For valves on equipment or against walls, sufficient standing space must be provided for operators. Overhead or仰天 (upward-facing) operation should be avoided, especially when handling acidic, alkaline, or toxic media, as this poses significant safety risks.

　　Gate valves shall not be installed upside down (with the handwheel facing downward), as this can result in long-term retention of the process medium in the bonnet space, leading to corrosion of the valve stem and contravening certain process requirements. Moreover, it significantly complicates packing replacement. For rising-stem gate valves, avoid underground installation to prevent corrosion of the exposed stem due to moisture. For lift-type check valves, ensure that the valve disc is installed vertically to allow smooth lifting and lowering. For swing-type check valves, ensure that the pivot pin is installed horizontally to facilitate free swinging. Pressure-reducing valves must be installed upright on horizontal pipelines, with no tilting in any direction.

　　2. Construction Operations

　　Installation and construction must be carried out with care; impact to valves made of brittle materials must be strictly avoided.

　　Before Installation

　　All valves shall be carefully checked to ensure that their model and specifications comply with the design requirements. (Based on the valve model and the manufacturer’s instruction manual, verify that they are suitable for the specified service conditions; where necessary, conduct hydrostatic or pneumatic pressure tests.) In addition, the packing shall be inspected for integrity, the gland bolts shall be checked for adequate adjustment clearance, and the valve stem and disc shall be examined for smooth operation, with no signs of jamming or misalignment.

　　(The valve disc sealing surface must be tightly closed; for valves with threaded connections, the thread quality shall be inspected. Nonconforming valves shall not be installed and must be separately stacked or clearly marked.) Remove any debris inside the valve.

　　Installation Process

　　When lifting the valve, do not attach the sling to the handwheel or stem to avoid damaging these components; instead, secure it to the flange.

　　The piping connected to the valve must be thoroughly cleaned.

　　Compressed air can be used to blow away iron oxide scale, mud, sand, welding slag, and other foreign matter. Such contaminants not only readily abrade the valve’s sealing surfaces, but larger particles—such as welding slag—can also clog small valves, rendering them inoperative.

　　When installing screw-type valves, wrap the sealing packing (hemp thread coated with aluminum grease or PTFE raw tape) around the pipe threads, taking care not to allow it to enter the valve body, as accumulation inside the valve could obstruct the flow of the process medium.

　　When installing flanged valves, ensure that the bolts are tightened symmetrically and evenly. The valve flange must be parallel to the pipe flange, with an appropriate gap, to prevent excessive stress on the valve that could lead to cracking. This is especially important for valves made of brittle materials or with low strength. For valves that are to be welded to the pipe, perform tack welding first, then fully open the closing element before completing the weld.

　　3. Protective Measures

　　Some valves also require external protection, namely thermal insulation and refrigeration. Sometimes, steam tracing lines are installed within the insulation layer. The decision as to which valves should be thermally insulated or refrigerated is based on production requirements.

　　In principle, whenever the temperature of the medium inside a valve drops excessively, thereby reducing production efficiency or causing the valve to freeze and fail, thermal insulation—or even heat tracing—must be provided. Conversely, when valves are exposed and such exposure is detrimental to production or leads to undesirable phenomena such as frost formation, cold insulation is required. Thermal insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, and vermiculite; cold insulation materials include cork, perlite, foam, and plastics.

　　4. Bypass and Instruments

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

　　5. Packing Replacement

　　Some valves in inventory have packing that is no longer effective, while others are incompatible with the service medium; therefore, the packing must be replaced.

　　Valve manufacturers cannot account for the myriad types of media used by end-users; therefore, standard packing is typically installed in the stuffing box. However, during operation, the packing must be compatible with the specific process medium.

　　When replacing the packing, it should be pressed in layer by layer. The joint between each layer is best set at a 45-degree angle, with adjacent layers staggered by 180 degrees. The packing height should allow for continued compression by the gland follower, while also ensuring that the lower portion of the gland bears down on the packing chamber to an appropriate depth—typically 10–20% of the total depth of the packing chamber. For valves with stringent requirements, the joint angle is 30 degrees, and the joints between adjacent layers are staggered by 120 degrees.

　　In addition to the packing materials mentioned above, depending on the specific application, other shaped packings may be used, such as rubber O-rings (natural rubber is suitable for weak alkali at temperatures below 60°C; nitrile rubber is suitable for oil-based fluids at temperatures below 80°C; fluororubber is suitable for a wide range of corrosive media at temperatures below 150°C), three-layer stacked PTFE rings (suitable for highly corrosive media at temperatures below 200°C), and nylon bowl-shaped rings (suitable for ammonia and alkali at temperatures below 120°C). 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 compressing the packing, the valve stem should be rotated simultaneously to ensure uniform compression all around and to prevent over-tightening; the gland follower should be tightened with even pressure and without tilting.