Valve Type for Prevention of Flow Reversal – Check Valves
axial check valve permit flow in one direction and prevent flow in the reverse direction. This is achieved through linear or rotary (angular) motion of a closure member that is kept open by the kinetic energy of the flowing fluid. When the flow is reduced towards zero or reversed the valve is automatically closed against its seat by gravity, the effect of supplementary springs, back pressure or combinations of these effects. Check valves are intended to prevent gross back flow of fluid and should not be relied on to provide effective isolation.
Check valves do not normally have shafts which breach the pressure containment except where this is necessary to provide mechanical override, position indication, or external damping or disk balancing. These features are usually only available on large swing check valves for critical applications. Shafts which penetrate the pressure containment should normally be avoided
Check valve types
Characteristics vary considerably and should be considered when selecting valves for particular applications.
Designs may be broadly categorised as follows:
Lift check (linear motion of the obturator in direction transverse to pipe axis.
Swing check (angular motion of the obturator).
Axial flow nozzle check (linear motion of the obturator along the pipe axis).
Plate check (linear motion of flexible metal or polymer plate along the pipe axis).
Diaphragm check (flexing of a membrane).