Inflow/Outflow Pipe Size
First, choose your pump carefully. Make sure that it is large enough to accomodate your needs. You can easily decrease pressure, but you cannot increase pressure if your pump is too small. Buy the largest pump you can afford for your system. The absolute minimum size pump to buy is one that recirculates your water once every two hours. Now for the pipe size. In order to get the most out of your pump, you need to fit it properly. The larger the pipe the more water pressure you will have. You lose pressure for each bend and each foot of lift (how high you go). Here are the friction loses for different size pipe. These are from a pipefitter manual.
a. First, find the equivalent loss from each joint. These numbers are in equivalent foot lenghts of straight pipe.
1" pipe: 90 bend 3', 45 bend 2', T-thru 3', T-bend 3', valve 1'.
1.5" pipe: 90 bend 4', 45 bend 2', T-thru 4', T-bend 4', valve 1'.
2" pipe: 90 bend 5', 45 bend 3', T-thru 3', T-bend 5', valve 2'.
2.5" pipe: 90 bend 7', 45 bend 3', T-thru 4', T-bend 7', valve 2'.
3" pipe: 90 bend 8', 45 bend 4', T-thru 5', T-bend 8', valve 2'.
b. Add up the total equivalent feet from all the joints and the total length of pipe.
c. Look up the right value from this list.
The numbers are for 0.75", 1', 1.25", 1.5", 2", 2.5", 3" pipe.
High numbers mean lots of drag and low numbers mean low drag.
0300 gph: 6.3, 1.9, 0.5, 0.3, xx, xx, xx
0600 gph: 23.1, 6.5, 1.8, 0.8, 0.1, xx
1200 gph: 73.5, 22.8, 6.2, 3.0, 0.8, 0.4, 0.1
1800 gph: xx, 48.1, 12.7, 6.3, 1.8, 0.8, 0.3
2400 gph: xx, 82.0, 21.6, 10.2, 3.0, 1.3, 0.4
3000 gph: xx, xx, 32.6, 15.4, 4.7, 1.9, 0.7
3600 gph: xx, xx, 45.6, 21.6, 6.4, 2.7, 0.8
4200 gph: xx, xx, xx, xx, 9.2, 4.0, 1.3
d. To find the losses in lift equivalent, look up the right value from the table and then compute B x C/100.
e. Add D to waterfall and/or stream height to get the total lift (head) equivalent drag on the pump.
f. Look at the performance table from the pump instructions to see the amount of water that will be delivered at the head computed in step f.
g. Repeat a-f for each pipe size under consideration. A preliminary c check is to see the pipe size where the high numbers for your pump size suddenly go low. Also compute the materials cost for each pipe size!
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