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Friction loss due to pvc pipe fittings
Friction loss through a fitting is expressed in equivalent "feet of head pressure."
Average Friction Loss for PVC and CPVC Fittings in Equivalent Feet of Straight Run Pipe
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Fitting |
PVC Nominal Pipe Size |
|
1/2" |
3/4" |
1" |
1 1/4" |
1 1/2" |
2" |
2 1/2" |
3" |
4" |
6" |
8" |
10" |
12" |
14" |
16" |
18" |
20" |
24" |
Tee Run |
1.0 |
1.4 |
1.7 |
2.3 |
2.7 |
4.0 |
4.9 |
6.1 |
7.9 |
12.3 |
14.0 |
17.5 |
20.0 |
25.0 |
27.0 |
32.0 |
35.0 |
42.0 |
Tee Branch |
3.8 |
4.9 |
6.0 |
7.3 |
8.4 |
12.0 |
14.7 |
16.4 |
22.0 |
32.7 |
49.0 |
57.0 |
67.0 |
78.0 |
88.0 |
107.0 |
118.0 |
137.0 |
90° Ell |
1.5 |
2.0 |
2.5 |
3.8 |
4.0 |
5.7 |
6.9 |
7.9 |
11.4 |
16.7 |
21.0 |
26.0 |
32.0 |
37.0 |
43.0 |
53.0 |
58.0 |
67.0 |
45° Ell |
.8 |
1.1 |
1.4 |
1.8 |
2.1 |
2.6 |
3.1 |
4.0 |
5.1 |
8.0 |
10.6 |
13.5 |
15.5 |
18.0 |
20.0 |
23.0 |
25.0 |
30.0 |
For example, if you had 50' of straight 1" pipe, then a 1" 90, then another 50' of pipe, your total feet of pipe would be 50' + 2.5' + 50' or 102.5' of pipe equivalent.
For example, if you had 10' of 2" pipe, going to a 2" Tee, and another 10' along the run of the Tee and 20' along the branch, your total would be 10' + 4' + 10' + 12' + 20' or 56' of pipe equivalent.
Now that you have the total equivalent feet of pipe, you can estimate the loss of flow as a percentage. In the first example, you'd have 100' divided by 102.5' or 97.56%. So if the charts show you can flow 50gph, you'd multiple that by .9756 and you'd get 48.78 gph. In the 2nd example you'd take 40' of pipe, divided 56' of equivalent pipe and you'd get 71%. So your flow would be .71 times what you would expect to get from just 40' of pipe. The flow charts on the flow chart page are per 100' of pipe. So if you look up 2", you'd see 3300gph through 100' of 2" pipe if just flowed by gravity. In his situation you'd multiple 3300gph x 71% (.71) and get 2357 gph per 100' of pipe when flowed by gravity alone. Since are using less than 100' of pipe total, you'd stop there. But if you had say 1000' of pipe. you'd have to do a friction loss calculation for the other 900' of pipe to get your total loss. (Or use the chart.)
Now you see why calculating flow through a pipe is so complicated. :-)
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