How to choose the correct pipe size

How To Choose The Correct
Pipe Size

A common mistake many homeowners and inexperienced contractors make is using too small of a pipe for the flow rate of their pump.  Always use the same size pipe, or even larger as the discharge port on the pumps.  

     Maximum  Water Flow Rates For Pipe

Pipe Size

Gallons Per Hour (GPH)
Gallons Per Minute (GPM)
1/2"
480
8
3/4"
900
15
1"
1,500
25
1 1/4"
2,700
45
1 1/2"
3,600
60
2"
5,400
90
3"
13,500
225
4"
21,000
350
6"
42,000
700

Head Loss (in feet) per 10 Feet of PVC Pipe

GPH
1"
1¼"
1½"
2"
3"
4"
6"
1,200
2.18
.56
.26
.08
-
-
-
1,800
-
1.19
.55
.16
.02
-
-
2,400
-
2.02
.94
.28
.04
-
-
3,000
-
-
1.05
.43
.07
.01
-
3,600
-
-
2.0
.58
.09
.03
-
4,200
-
-
-
.78
.11
.03
-
4,800
-
-
-
.99
.14
.04
-
5,400
-
-
-
1.24
.18
.05
-
6,000
-
-
-
1.50
.22
.06
.01
7,500
-
-
-
-
.33
.10
.01
9,000
-
-
-
-
.46
.13
.02
10,500
-
-
-
-
.62
.18
.02
12,000
-
-
-
-
.79
.21
.03

 

Head pressure is most often calculated in terms of actual vertical lift - the height water is being lifted. But, for a complete and accurate measurement of Total Dynamic Head Pressure, we have to also add in the Head Pressure or Loss created by the pipe itself. As water passes through pipe, friction reduces flow rate. The diameter and length of pipe can have a significant effect on the Total Dynamic Head Pressure.


How to choose the correct size pipe for your pump, pond, and waterfalls.Total Dynamic Head Pressure is the feet of Head (vertical rise) added to the friction loss created by the pipe. In most water features with relatively small runs (length of pipe), as long as you use pipe no smaller than the pump's discharge you will be fine. In larger installations with higher flow rates, taller heights and longer runs, the friction loss from the pipe can drastically reduce the flow rate that you may be trying to achieve.

To calculate Total Dynamic Head, add the Head (vertical lift) AND the horizontal Head Loss of the pipe diameter and length of the run.

For example, a 5,400 gph pump pushing water with vertical lift of 6 feet and a distance run of 75 feet would have a Total Dynamic Head of 15.30 Feet with 2" pipe, but would only have 7.35 Feet of Head with 3" pipe.


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