Check valve at pipe closes slower than check valve at pump


I am running tow different scenarios. A pump shutdown with a pump check valve and a pump shutdown and startup with a pipe check valve and the check valve at the pipe closes slower than the check valve at the pump every time. I know that Hammer models the pipe check valve at the midpoint in the pipe so I would have assumed that the pipe check valve would be the first to close since both types of valves are programmed to close at the first detection of reverse flow. I tried to model the pump shutdown pattern as similar to the ramp down driven by the inertia. 

But, no matter how I change the pattern for the pump shutdown and startup, the check valve at the pipe always closes after the pump speed has reached zero. So, for example under my first pattern, the pump would reach a speed of zero after 12 seconds and the check valve would close at 12.6 When I change the pattern to have the pump speed reach zero after 8 seconds now the check valve closes at 11.7 s. But when I use a pump check valve, the check valve closes after 11 s when the pump speed is still 190 rpm. 

Any idea what's going on?



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