Selection of valves and design of pipes shall comply with the following principles:
1. In terms of locations and purposes of valves, the suitable valves can be selected after knowing relevant specification, size,standards, principle and permission.
2. Need to specify the working condition, applicable medium, working pressure and working temperature of media.
3. Need to specify the nominal diameter to match the pipeline: DN（mm）
4. Need to specify the connecting type of the pipeline, including flange type, inside&outside screwed type, welded type, wafer type, clip type, groove type,and union type, etc.
5. Need to specify the operating type of the valve, including lever, worm gear, pneumatic actuator, hydraulic actuator, electromagnetic actuator and electromagnetic-hydraulic actuator, etc.
6. Need to specify the model of the valve, including gate valve, globe valve, ball valve, butterfly valve, and check valve, etc.
7. Need to specify the working type of valve, including on-off type, adjusting type, safety type, etc.
8. Need to specify material of body and trim, including grey iron, ductile iron, carbon steel, alloy steel, stainless steel, monel alloy,copper alloy, aluminum alloy, etc.
9. Need to specify the requirements on seal performance and grade or leakage.
10. Need to specify the requirements on coating, packing and transportation.
11. Need to specify face to face dimension, height, outline sizes, flow resistance, drainage ability, flow characteristic, protected grade, anti-explosive performances, etc.
12. Need to specify the installed position and direction for the valve.