Check Valves

Description

Check valves are self activating safety and flow sensitive devices, which allow flow of fluid through them in a single direction only; thus they automatically prevent the reverse flow. These valves are also referred as non return valves, clack valves and one way valves. The valves consist of guard cage, spring, valve disc, retaining ball, seat and two port valves (one for fluid entry and other for fluid exit). Usually the diameter of ball that sits on the seat is larger than the through-hole. The operation of check valves is that the flow of liquid in valve is allowed only when pressure below the seat exceeds that of above the ball; once pressure above the ball exceeds that of below the seat, the ball returns to the seat, thus forming a seal and preventing the reverse flow.

Types

Check valves are classified as: 

• Ball check valves
• Diaphragm check valves
• Swing check valves
• Clapper check valves
• Stop check valves
• Lift check valves
• Wafer check valves
• Disc check valves
• Split disc check valves

Advantages 

• Relief of vacuum conditions
• Prevents fluid reverse flow when system is off and thus protects equipment like control valves and flow meters
• Prevents flooding and flow under gravity
• Checks pressure surge accompanied by hydraulic forces as in water hammer

Applications

Check valves are used in many fluid based industries such as chemical, power plants and are most often used in pumps such as diaphragm driven pumps. Pumps for chromatography use ball check valves. Drip irrigation system and irrigation sprinklers use check valves to keep lines from draining when the system is off. Check valves are also part of common house hold items. Check valves are installed in individual gas sources to prevent mixing of gases. Check valve applications also include vacuum breakers, cooling towers, boilers, pressure pumps and nitrogen purge lines.