Page 156 - Valve Selection Handbook

4

CHECK VALVES

FUNCTION OF CHECK VALVES

Check valves are automatic valves that open with forward flow and
close against reverse flow.
This mode of flow regulation is required to prevent return flow, to
maintain prime after the pump has stopped, to enable reciprocating
pumps and compressors to function, and to prevent rotary pumps and
compressors from driving standby units in reverse. Check valves may
also be required in lines feeding a secondary system in which the pres-
sure can rise above that of the primary system.

Grouping of Check Valves

Check valves may be grouped according to the way the closure member
moves onto the seat. Four groups of check valves are then distinguished:

1. Lift check valves. The closure member travels in the direction nor-
mal to the plane of the seat, as in the valves shown in Figure 4-1
through Figure 4-7.
2. Swing check valves. The closure member swings about a hinge,
which is mounted outside the seat, as in the valves shown in Figure
4-8 through Figure 4-10.

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