# How sensitive is downstream pressure to flow diverted through an upstream branch?

1. Dec 11, 2012

### yaboynate

I have a somewhat theoretical question based on a real world problem regarding a gravity-fed domestic water system:

I have a very large tank (~10,000 gal) at 300' elevation supplying water to a piping system consisting of a 6" line coming down from the tank to a tee at 100' elevation. Branch 1 from the tee has a varying demand on the system in a 2" line. Branch 2 runs down to a closed valve at 80' and is also a 2" line. What is the static pressure at the closed valve when the Branch 1 demand is 5 gpm? 10 gpm? 20 gpm?

The real world basis is that I have these 50 psi swings (40 - 90 psi) in system pressure at my closed valve. I'm trying to determine if upstream demands could cause this and if so, how much.

Any help would be greatly appreciated.

Thanks,

Nathan

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