Inspection before installation
There are many types, models and specifications of commonly used valves. The type of valve to use should be selected according to the purpose of the valve, the characteristics of the medium, the maximum working pressure, the maximum temperature, the flow rate and flow rate of the medium or the nominal diameter of the pipe.
Before installation, carefully check whether the models and specifications of all valves meet the design requirements. According to the valve model and factory instructions, check whether they can be used under the required conditions, and conduct water or air pressure tests if necessary. In addition, check whether the packing is in good condition, whether the gland bolts have sufficient adjustment margin, and check whether the valve stem and valve disc are flexible, whether there are jams or distortions. The sealing surface of the valve disc must be tightly closed. For valves connected with threads, the thread quality should be checked. Unqualified valves cannot be installed and should be stacked separately or marked.& nbsp;
Precautions when installing valves
Open stem valves cannot be laid directly underground, to prevent corrosion of the valve stem, it can only be installed in a covered trench, and the valve should be installed in a position convenient for operation, inspection, disassembly, maintenance and operation.
Do not throw the valve casually when handling it to avoid damage and deformation.When stacking, carbon steel valves should be separated from stainless steel valves and non-ferrous metal valves. When lifting the valve, the steel wire rope should be tied to the connecting flange between the valve body and the bonnet. Do not tie it to the handwheel or valve stem to prevent damage to the valve stem and handwheel.& nbsp; The valve installation position should not hinder the disassembly, maintenance and operation of equipment, pipelines and the valve itself.The installation height should be convenient for operation and maintenance. Generally, the valve operating handle should be 1-1.2m away from the ground. For valves with many operations, when they must be installed more than 1.8m away from the operating surface, a fixed operating platform should be installed. When they must be installed above or below the operating surface, an extension rod should be installed or the valve stem should be installed horizontally, and at the same time, a handwheel with a transmission device or a remote operating device should be installed. The included angle between the axis of the valve transmission device should not exceed 30°, and the joint should be flexible to rotate, flexible and easy to use during operation, and accurate instructions. For valves with thermal displacement, the transmission device shall have compensation measures.
In horizontal pipes, it is best to have the valve vertically upwards or the valve stem installed within the upper semicircle, but the valve stem must not be installed downward.Valve stems and handwheels on vertical pipes must be installed in the direction of the operation circuit line. When conditions permit, valves should be installed as centrally as possible for easy operation. Valves on pipelines in the tower area above 4 meters above the ground should not be placed outside the platform for ease of installation and operation.
For directional valves, the installation direction should be determined according to the medium flow direction of the pipeline during installation. For example, when installing a stop valve, the medium should flow from below the cabinet plate to above, commonly known as low inlet and high outlet.When installing cocks and gate valves, allow medium to flow out from either end. When installing a check valve, special attention must be paid to the flow direction of the medium to ensure that the valve disc can automatically open. On important occasions, arrows must be clearly marked outside the valve body to indicate the direction of medium flow. For swing check valves, ensure that the rotating pivot of the insert plate is installed in a horizontal position. For lifting check valves, ensure that the center line of the valve disc is perpendicular to the horizontal plane.
For valves with special requirements, be familiar with installation requirements.如安装杠杆式安全阀和减压阀时，必须使阀盘中心线与水平面相互垂直，发现倾斜时必须进行校正。
When installing threaded valves on pipes, be sure to install a union near the valve for easy disassembly.
Shut-off valves shall be set up for auxiliary system pipes entering the workshop. When the workshop is shut down for maintenance, they can be cut off from the main pipe.These valves are generally installed at a high height and should be arranged together as much as possible to allow for a fixed operating platform.
Install flanged valves to ensure that the two flange end faces connected to them are parallel and coaxial with the valve flange.Especially when installing valves with brittle materials such as cast iron, valve damage caused by incorrect installation position and uneven stress should be avoided. When tightening the flange bolts, a symmetrical or cross-crossing method should be used and gradually tightened in several times.
安装高压阀门前，必须复核产品合格证和试验记录。高压阀门多为角阀，使用时常为两只串联，开启时启动力大，必须设置阀架以支承阀门和减少启动应力，其安装高度以0.6-1.2m为宜。
机泵、换热器、塔和容器上的管接口不应承受阀门和管道的重量，公称直径dn>80mm的阀门应加设支架。
衬里、喷涂及非金属材质问门本身质量大，强度较低，除考虑工艺要求外，应尽可能做到集中布置，便于阀架设计。即便是单独一个阀门也应固定在阀架上。水平管道上安装重型阀门时，要考虑在阀门的两侧装设支架。
安装螺纹连接的阀门应保证螺纹完整无缺，要根据工作条件选用填料，拧紧到位时阀杆的位置应符合安装要求。拧紧时，必须用扳手咬牢拧人管子一端的阀门六方体上，以保证阀体不致拧变形和损坏。法兰或螺纹连接的阀门应在关闭状态下安装。
Argon arc welding should be used for the back sealing of the connection seam between the valve and the pipeline to ensure that the interior is smooth and smooth.The valve should not be closed during welding to prevent overheating and deformation of the sealing surface. If the sealing material is not resistant to high temperatures, the sealing material must be removed before welding to prevent the welding temperature from damaging the sealing material.
For valves on side-by-side pipelines, the clear distance between handwheels shall not be less than 100mm,In order to reduce pipe spacing, it is best to staggered valves arranged side by side.
Before positioning, the cryogenic valve should be opened and closed as much as possible in cold conditions, and it is required to be flexible and free from jamming.
安全阀的连接处应有弯头（或者三通之类的配件）Avoid fluid directly impacting the valve; in addition, ensure that the safety valve is not frosted during operation to avoid failure during operation.
It is strictly prohibited to use the valve stem as a scaffold to climb during valve installation.
High temperature valves above 200℃Since the valve is installed at room temperature, but after normal use, the temperature rises, the valve bolt expands by heat, and the gap increases, so it must be tightened again, which is called "hot tightening". Operators should pay attention to this work, otherwise valve leaks will easily occur.
In cold winter, if the water valve is closed for a long time, the accumulated water behind the valve should be drained.After the steam valve is stopped, the condensate must also be drained. The bottom of the valve is like a drain switch that can be turned on to drain water.
Non-metallic valves, some are hard and brittle, and some are low in strength. When operating, the opening and closing force should not be too large, especially not violent.Also pay attention to avoid bumping objects.
The flow direction of the stop valve during installation should be consistent with the arrow marked on the valve body (it cannot be installed backwards), so that when the valve is closed, pressure is applied to the cone at the top of the valve, and the packing is not under load. However, for valves (such as heating valves) that are not frequently opened and closed but need to be strictly ensured that there is no leakage in the closed state, they can be consciously reversed according to needs to make them tightly closed with the help of medium pressure.
大规格的闸阀（DN200-500MM)、气动调节阀应该竖装，以免因阀芯的自重较大而偏向一方，增加阀芯与衬套之间的机械磨损，造成泄漏。
在拧紧压紧螺钉时，阀门应处于微开状态，以免压坏阀顶密封面。
所有阀门就位后，应再作一次启闭，灵活无卡住现象为合格。
After naked cooling of a large air separation tower, pre-tighten the connecting valve flange once in the cold state,Prevent the valve from leaking at normal temperature but leaking at low temperature.
When using the new valve, do not press the packing too tightly,The principle of no leakage is to prevent the valve stem from being under too much pressure, causing accelerated wear, and making it difficult to open and close.
