Calculating closure time for check valves

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A WORKED EXAMPLE – CHECK VALVE SLAM PREDICTION The information that follows is based on an application where the potential for damaging surge conditions within a Sewage Pumping Station was determined by a surge analysis report: 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^2 With a typical flow velocity of 2.00 m/s, i.e. a deceleration rate of 1.33 m/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.

Please Note – actual application data for the above example is considered confidential. For further information and an introduction to the relevant water authority please contact MGA Controls Limited referring to the above Application Reference.


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