Ten seconds is a slow closing time but keep in mind that the majority of the actual closure occurs in a small final percentage of that total time.

In that 2L/c calculation, L is the distance to a major reflection point such as the upstream source or major change in flow area. L is not the length of the run between an elbow-elbow pair.

On hammer analyses, start with the longest run between elbows first. These runs have the longest imbalance and the longer imbalances excite the lower modes of system vibration which should have the larger system participation in the event. The event in that 20 meter run is probably over too quick to get your system excited.

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