（1） Direction and location



Many valves have directionality, such as globe valve, throttle valve, pressure reducing valve, check valve, etc. if they are installed reversely, the service effect and service life will be affected (such as throttle valve), or they will not work at all (such as pressure reducing valve), or even cause danger (such as check valve). For general valves, there is a direction mark on the valve body; in case there is no direction mark, it should be correctly identified according to the working principle of the valve. The valve cavity of the stop valve is asymmetric, and the fluid should be allowed to pass through the valve port from bottom to top. In this way, 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 why the stop valve cannot be reversed. Other valves also have their own characteristics.



The valve installation position must be convenient for operation: even if the installation is temporarily difficult, the long-term work of the operator should be considered. It's better to make the valve handwheel flush with the chest (generally 1.2m away from the operation floor), so that the opening and closing of the valve is less effort. The hand wheel of the floor valve should be upward, not inclined, so as to avoid the operation. The valve of wall machine and equipment should also leave room for operators to stand. To avoid the sky operation, especially acid-base, toxic media, etc., otherwise it is not safe. Do not install the gate upside down (i.e. the hand wheel is downward), otherwise the medium will remain in the valve cover space for a long time, which is easy to corrode the valve stem, and is taboo for some process requirements. It is very inconvenient to change the packing at the same time. Do not install the rising stem gate valve underground, otherwise the exposed stem will be corroded due to moisture. Lift check valve, installation to ensure that its disc vertical, in order to lift flexible. Swing check valve, installation to ensure its pin level, in order to swing flexible. The pressure reducing valve shall be installed vertically on the horizontal pipeline, and shall not be inclined in all directions.



（2） Construction operation



During installation, care must be taken to avoid hitting the valve made of brittle materials.



Before installation, the valve shall be inspected to check the specification and model and identify whether it is damaged, especially for the valve stem. Also rotate a few times to see if it is askew, because during transportation, it is easy to bump the valve stem askew. Also remove the debris in the valve.



When lifting the valve, the rope should not be tied on the hand wheel or stem to avoid damaging these parts, but should be tied on the flange.



The pipeline connected to the valve must be cleaned. Compressed air can be used to blow away iron oxide chips, mud sand, welding slag and other debris. These debris, not only easy to scratch the sealing surface of the valve, in which large particles of debris (such as welding slag), but also block the small valve, making it ineffective. When installing the screw valve, the sealing packing (thread hemp, aluminum oil or polytetrafluoroethylene raw material belt) should be wrapped on the pipe thread. Do not get it into the valve, so as to avoid accumulation in the valve and affect the medium circulation.



When installing the flange valve, pay attention to tighten the bolts symmetrically and evenly. Valve flange and pipe flange must be parallel with reasonable clearance to avoid excessive pressure and even cracking of the valve. For brittle materials and low strength valves, special attention should be paid. For valves to be welded with pipes, spot welding shall be carried out first, then the closing parts shall be fully opened, and then the welding shall be completed.



（3） Protective measures



Some valves must also have external protection, which is insulation and cold insulation. Sometimes, hot steam pipeline is added in the insulation layer. What kind of valve should be heat preservation or cold insulation, according to production requirements.



In principle, if the temperature of the medium in the valve is too low, which will affect the production efficiency or freeze the valve, heat preservation or even mixing is needed; if the valve is exposed, which is unfavorable to the production or causes frosting and other adverse phenomena, cold preservation is needed. Thermal insulation materials include asbestos, slag cotton, glass wool, perlite, diatomite, vermiculite, etc. cold insulation materials include cork, perlite, foam, plastic and so on.



（4） Bypass and instrumentation



Some valves, in addition to the necessary protection facilities, also have bypass and instrument. Bypass is installed. Convenient for maintenance of drain valve. Other valves are installed with bypass. Whether to install bypass depends on valve condition, importance and production requirements.



（5） Packing replacement



Inventory valve, some packing has been difficult to use, and some do not match the use of media, which requires replacement of packing.



Valve manufacturers can not consider the use of thousands of different types of media, stuffing box is always filled with ordinary packing, but when using, must make the packing adapt to the media.



When changing the packing, press it in circle by circle. The joint of each circle should be 45 degrees, and the circle should be 180 degrees apart. The packing height should consider the space for the gland to continue to press. At present, the lower part of the gland should be allowed to press the packing chamber to an appropriate depth, which can generally be 10-20% of the total depth of the packing chamber. For highly demanding valves, the joint angle is 30 degrees. The joints between the rings are staggered by 120 degrees. In addition to the above fillers, rubber O-ring (natural rubber resistant to weak alkali below 60 ℃, NBR resistant to oil crystal below 80 ℃, fluororubber resistant to various corrosive media below 150 ℃) three piece stacked PTFE ring (resistant to strong corrosive media below 200 ℃) nylon bowl ring (resistant to ammonia and alkali below 120 ℃) and other forming fillers can be used according to specific conditions. A layer of polytetrafluoroethylene raw material belt is wrapped outside the ordinary asbestos packing, which can improve the sealing effect and reduce the electrochemical corrosion of the valve stem.



When pressing the seasoning, turn the valve stem at the same time to keep it even all around and prevent it from being too dead. Tighten the gland evenly and do not tilt.