(I) direction and position


Many valves have directionality, such as stop valve, throttle valve, pressure reducing valve and check valve. If they are installed reversely, the service effect and life (such as throttle valve) will be affected, 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; if not, it shall be correctly identified according to the working principle of the valve. The valve cavity of the stop valve is not symmetrical. The fluid should be allowed to 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 (due to the upward pressure of the medium), and the medium is not pressurized after the closing, which is convenient for maintenance. This is the reason why the stop valve cannot be reversed. Other valves have their own characteristics.


The installation position of the valve must be convenient for operation: even if the installation is temporarily difficult, the long-term work of the operator should also be considered. It is better to make the hand wheel of the valve flush with the chest (generally 1.2m away from the operating floor), so that the opening and closing of the valve is more economical. The hand wheel of landing valve shall face up, and do not tilt to avoid awkward operation. The valve of the wall leaning machine and the equipment shall also leave room for the operator to stand. It is not safe to operate in the sky, especially in acid and alkali, toxic media, etc. Do not install the gate upside down (i.e. the hand wheel is downward), otherwise, the medium will be left in the valve cover space for a long time, which is easy to corrode the valve stem, and is forbidden by some process requirements. At the same time, it is inconvenient to change the packing. Open stem gate valve shall not be installed underground, otherwise exposed stem will be corroded due to humidity. When installing the lift check valve, make sure that the valve disc is vertical, so that the lift is flexible. The swing check valve shall be installed with its pin shaft horizontal so that it can swing flexibly. The pressure relief valve shall be installed vertically on the horizontal pipeline and shall not be inclined in all directions.


(II) construction


The installation and construction must be careful to avoid hitting the valve made of brittle materials.


Before installation, check the valve, check the specification and model, and identify whether there is any damage, especially for the valve stem. Also rotate a few times to see if it is skewed, because in the process of transportation, it is most likely to hit the skewed stem. Also remove the debris from the valve.


When lifting the valve, the rope shall not be tied on the hand wheel or stem, so as to avoid damage to these parts, and it shall be tied on the flange.


The pipeline connected to the valve must be cleaned. Compressed air can be used to blow away iron oxide scraps, mud sand, welding slag and other sundries. These sundries are not only easy to scratch the sealing surface of the valve, but also can block the small valve and make it invalid. When installing the screw valve, the sealing packing (thread hemp and aluminum oil or polytetrafluoroethylene raw material belt) shall be wrapped on the pipe thread, and shall not be put into the valve, so as to avoid the accumulation in the valve and the influence of medium circulation.


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


(III) protection measures


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


In principle, if the medium in the valve reduces the temperature too much, which will affect the production efficiency or freeze the valve, it needs to keep warm, or even mix with heat; if the valve is exposed, which is adverse to production or causes frost and other adverse phenomena, it needs to keep cold. Thermal insulation materials include asbestos, slag cotton, glass wool, perlite, diatomite, vermiculite, etc. cold insulation materials include cork, perlite, foam, plastic and so on.


(IV) bypass and instrument


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


(V) packing replacement


Inventory of valves, some packing has been difficult to use, some with the use of media is not consistent, which requires the replacement of packing.


The valve manufacturer can't consider using different media of thousands of doors and thousands of types. The stuffing box is always filled with ordinary packing, but when using, the packing must be suitable for the media.


When replacing the packing, press it in circle by circle. Each circle of joint should be 45 degrees, and the circle and the circle should be 180 degrees apart. The packing height should consider the space for the gland to continue to press. At present, it is necessary to make the lower part of the gland press the packing chamber to a proper depth, which can generally be 10-20% of the total depth of the packing chamber. For valves with high requirements, the joint angle is 30 degrees. The joints between the rings shall be staggered by 120 degrees. In addition to the above fillers, according to the specific conditions, three pieces of laminated polytetrafluoroethylene ring (resistant to strong corrosive media below 200 ℃) nylon bowl ring (resistant to ammonia and alkali below 120 ℃) and other shaped fillers can also be used (resistant to weak alkali below 60 ℃, oil crystal below 80 ℃, and various corrosive media below 150 ℃). A layer of polytetrafluoroethylene raw material tape is wrapped outside the ordinary asbestos packing, which can improve the sealing effect and reduce the electrochemical corrosion of the valve rod.