Construction of a Check Valve
Advantages of Check Valves
Disadvantages of Check Valves
Types of Check Valves
Swing Check Valve
|Fig. A: Swing check valve|
Lift Check Valve
|Fig. B: Lift check valve|
|Fig. G: Wye-pattern lift check valve|
Tilting Disc Check Valve
|Fig. C: Tilting-disc check valve|
Folding Disc Check Valves
|Fig. D: Folding-disc check valve|
Vertical or In-Line Check Valve
Stop Check Valve
|Fig. E: Swing-disc stop check|
|Fig. F: Wye-pattern stop check|
The flow velocity of the fluid through the valve has a significant effect on the life of the check valve. The valve should be sized such that the fluid velocity under normal conditions is sufficient to keep the disc fully open and pressed against the stop. This minimizes disc fluttering, which is the primary cause of valve failure. Also, a check valve should not be located immediately downstream of a source of turbulence, such as a pump, elbow, control valve, or a tee-branch connection.
It is recommended that manufacturer’s recommendations be followed to provide the required straight run of pipe upstream of the check valve. Some manufacturers recommend 8-to-10 pipe-diameter length of straight run of pipe upstream of the valve. Sometimes, the layout and the space available may not allow compliance to manufacturer’s recommendations. Alternatives must be evaluated and the most reasonable and feasible approach be implemented.
A swing check valve may be used in the vertical run of a pipe only when the flow is upward. In addition, the flow velocity and the fluid pressure must be adequate to overcome the disc weight and swing it to the fully open position. In-line ball check valves are suitable for application in horizontal or vertical lines.
When the flow is suspected to be pulsating and low, use of a swing check valve is not recommended. Due to the continuous flapping of the swing disc against the seat, valves suffer considerable damage, and at times the swing discs can come loose.
|Table 1: Application of Check Valves|