Valves are installed in various piping systems to control the pressure, flow rate, and direction of flow. Because the medium pressure, flow, temperature ,physical and chemical properties are different, the control requirements and use requirements for the fluid system are not the same, so the valve type and structure of the valve are not the same too.

Therefore, how to select the valve correctly is the key to realize the sealing performance, strength performance, control performance, movement performance and flow performance of the valve.For most of valves, valve sealing problem is the primary problem. The external leakage or internal leakage due to poor sealing performance or sealing life , will cause environmental pollution and economic losses;

The leakage of medium with toxic ,harmful , corrosive ,flammable and explosive performance may cause great economic losses and even personal injury.  For high pressure gas valves and safety valves, valve safety and reliability is very important.

Therefore, great attention must be paid to the correct selection of valves.