Wondering if there was equation to solve for pressure surges for gases (natural gas in my case) on slow closing valves. 
As the only ones I have found is for imcompressible fluids: P = 0.07VL / t + P1, where P1 is the inlet pressure, V is the flow velocity in ft/sec, t is the Globe valve closing time in seconds and L is the upstream pipe length in feet.
It may be correct o say dry natural gas under stable conditions may not give rise to surges. You can get surges from slugs of liquids in gas pipelines. That is why they invented "slug catchers".
Two phase flow will give you surges. This is a very complex subject.
The original posting said the gas was "natural gas". Until processed natural gas contains liquids. I was just trying to warn the original poster of issues that may have not been considered.

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