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Old 01/10/2008, 07:50 PM   #30
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Join Date: Dec 2002
Location: Maumee, OH
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Originally posted by not_sponsored
If you're pumping 1200 gph in the pipe, the difference between a 1.5" pipe and a 3" pipe is 2.5 feet of head per 100 feet of pipe. In this case you'll be working with less than 10 feet of pipe or .25 feet less head by switching from a 1.5" pipe to a 3" pipe, TWICE THE DIAMETER.

On the other hand, lets say we have 5 90 degree fittings, for 1.5" pipe that would add 4 feet of head for every 90, or 20 feet of head.

Using 3" pipe we would add 7.9 feet of head for every 90 or 39.5 feet of head.

This is a difference of 19.5 feet for the different sized pipes, for MINOR head loss. Compare this with the .25 feet of head loss caused by decreasing the pipe size in MAJOR head loss.
Sorry to say but you are rading the equivalent lenght of fittings table wrong.
The table of equivalents will give you the equivalent in lenght of stright pipe not of feet of head loss.

A 3" 90* elbow is equivalent to 7.9 feet of stright 3"pipe and a 2" 90* elbow is equivalent to 5.7 feet of stright 2" pipe, a 11/2" 90* elbow is equivalent to 4 feet of stright 11/2" and so on.

Eventhough the equivalent straight pipe is higher the pressure loss is lower.
At a flow of 1200 gph .
7.9 feet of 3" pipe will have 0.0079 ft of head pressure drp
5.7 feet of 2" pipe will have 0.0456 ft of head pressure drop
4 feet of 11/2" pipe will have 0.104 ft of head pressure drop.

So in other words a 90* 11/2" elbow will have a head pressure loss that is 2.3 times larger than a 2" elbow.

If you drop the diameter to 1" that difference comes to that a 1" 90* elbow (2.5 ft equivalent) will have a pressure drop of 0.53 ft of head which is 11.6 times higher than the pressure drop across a 2" elbow eventhough its equivalent lenght is only 2.5 ft compared to the 5.7 feet of 2" elbow.

Did I write what I wrote? What the heck am I talking about! Well..... Nevermind.

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