Check Valve Deceleration / Dynamic Studies

..."Pump Non-Return Valves

The analysis has shown the pump non-return valves must be capable of matching a rate of flow decay of 2.45 m/s (based on nominal 400mm i.d. Ductile Iron pipework) to zero in 0.21 seconds. This equates to a flow deceleration of 11.60 m/s

With a typical flow velocity of 2.00 m/s, i.e. a deceleration rate of 1.33m/s*2, a standard swing check valve is normally capable of closure in approximately 1.5 seconds from a fully open position. As a result of the analysis a rapid acting spring assisted type check valve was recommended on all pumps.

Calculations

Initial flow rate of 2.45 m/s (8.04 fps) will decelerate to zero in 0.21 seconds
Deceleration of 11.6 m/s*2 (38.1 ft/s*2).

According to the dynamic characteristic curves below, the Surgebuster should only allow about 0.6 fps of reverse flow before closing. Projecting the curve out for the standard Swingflex indicates that it would allow about 2.6 fps of reverse flow before closing."...

With reference to the above table:

Flow Deceleration at 38 fps*2 Ξ 2.6 fps (high into ‘severe slam’)

Time to Closure:

Reverse Velocity at Time of Closure / Deceleration + Initial Time of Flow Decay = Time to Closure

2.6 fps / 38 fps*2 + 0.21s = 0.28 s

From the Joukowski equation, Pressure Surge:

h= av/g

a – pipe wave velocity
v – reverse velocity
g – gravity 9.8m/s*2 (32.2 fps*2)

h = 3714 x 2.6/32.2 = 299.9
299.9 x 0.4335 = 130.0 psi = 9.0 Bar*

https://www.mgacontrols.com/a-worked-example-check-valve-slam-prediction/

https://www.epj-conferences.org/articles/epjconf/pdf/2017/12/epjconf_efm2017_02036.pdf

https://awwa.onlinelibrary.wiley.com/doi/abs/10.1002/j.1551-8833.2007.tb07888.x

I like this old school simple explanation. Anyway, thanks for posting these amazing articles.

Improper sizing of check valves results in check valve slam, a phenomenon that produces undue increase in pressure head due rapid decrease in reverse flow velocity associated with check valve closure. Check valves are placed in pipe systems to prevent flow reversal. However, most check valves require a finite time to activate after sensing flow reversal and the flow could develop significant velocity in the reverse direction before the valve is completely closed. This reverse flow velocity is brought to rest when the valve is closed completely. The rapid change in reverse flow velocity produces a rapid increase in pressure head. The reverse flow velocity at the time of complete closure depends on several factors including the pump inertia, steady state head and flow values in the pipe system, length of liquid column to the source of major wave reflection such as a reservoir, friction losses in piping systems, slope of pipeline, and wave celerity.