1. The verticality of the flange surface and the center line of the piping and the error of the flange bolt hole should be within the allowable value. After the valve and the center line of the piping are consistent, it will be installed. 

 2. When tightening bolts, use a wrench that matches the nut. When using hydraulic and pneumatic tools for fastening, be careful not to exceed the specified torque. 

 3. When connecting the two flanges, first of all, the flange sealing surface and the gasket should be evenly pressed, so as to ensure that the flange is connected by the same bolt stress. 

 4. The tightening of flanges should avoid uneven force, and should be tightened in the order of symmetry and intersection. 

 5. After the flange is installed, make sure that all bolts and nuts are evenly fastened. 

 6. For the fastening of bolts and nuts, washers should be used to prevent loosening caused by vibration. In order to avoid the adhesion between the threads at high temperature, anti-stick agent should be applied to the thread part during installation. 

 7. For high-temperature valves above 300℃, flange connection bolts, valve cover fastening bolts, pressure seals and packing cover bolts must be tightened again after the temperature rises. 

 8. When the low temperature valve is installed, it is in the state of atmospheric temperature. Due to the formation of temperature difference, flanges, gaskets, bolts and nuts shrink, and because the materials of these parts are different. 

 9. The respective line expansion coefficients are also different, forming environmental conditions that are very easy to leak. From this objective situation, when tightening the bolts at atmospheric temperature, the moment that takes into account the shrinkage factors of each component at low temperature must be adopted.