Calculating GPH
 

I hopefully have a simple question. If I have a 1 foot run of 1” pipe followed by 1 foot run of ¾” pipe followed by another 1 foot run of 1” pipe do I calculate the GPH by using the smallest diameter pipe, or do I calculate it for each and add them together?
Example:
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What gets me confused is in this case wouldn’t the friction loss be less than if the whole pipe is ¾”?

If you want an exact answer, you'd figure out the pressure drop for each section and add it up. For over-designing, just use the 3/4" to figure out the pressure drop and just know that your flow will actually be higher. HOWEVER, you are going to have to take into account those reducers. There is a pretty decent headloss calculator floating around out there that can do all that for you. I can't find the site at the moment but I think it was an excel sheet in an article by Sanjay.

Thanks Steve! After googling his name I found this:
http://www.advancedaquarist.com/issu.../featurejp.htm

I good read plus the Excel is near the bottom.

No problem! That's the one I was remembering. Pretty all out spreadsheet huh? Super handy!