Check Valves allow medium to flow in one direction only, stop medium which flow in opposite direction .usually these valve work automatically. Under the action of pressure of fluid which flow in one direction, the disc open. When fluid flow in opposite direction .the fluid is cut down by the pressure of fluid and self-gravity
The check valve include swing type and lift type . Swing check valve have an articulated mechanism and a disc which leant on surface of slop seat freely . The disc is connected with articulated mechanism to make sure disc can reach right place on seat every time .so that disc have enough space to swing and can contact with seat veritably in full-scale . According to the requirement , disc can be made from metal , metal embed in leather or rubber or compound .when check valve open completely ,fluid pressure have little resistance, therefore the pressure drop through valve is relative small.
Disc of lift check valve is on the seal face of seat .It?ˉs disc can up and down freely . fluid pressure make disc rise from seal face of seat , the backflow of medium make disc back to seat and the fluid can be cut down .so it like globe valve except moving type of disc . According to the using requirement , disc can be made from metal , metal embed in rubber insert or rubber ring .
Just like globe valve ,lift check valve have narrow channel ,so pressure of fluid in lift check valve is bigger than swing check valve . swing check valve have fewer restrictions in flow rate.
Check valve with different materials can be used in pipe with various medium. Check valve become one of fluid parts of the complete pipeline when check valve is installed. The state of valve will be influenced by transient flow state of system it work .while, state of valve can affect transient flow state of system.
Check valve is also called reflux valve , inverted valve , counterbalance valve , non return valve, this kind of valve open and close by power caused by fluid in pipeline .usually these valve work automatically. Welding lift angle check valves in pipe system is used to prevent backflow of medium and rollback of pump and bleed of medium in vessel. It also used in pipe which provide supplies to supporting system.

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