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Assume Gravity Flow. About 6f/s flow velocity, also suction side of pump |
Assume Average Pressure. (20-100PSI) About 12f/s flow velocity |
Assume "High Pressure" PEAK flow. About 18f/s flow velocity* |
| Sch 40 Pipe Size |
ID
(range) |
OD |
GPM
(with minimal pressure loss & noise) |
GPH
(with minimal pressure loss & noise) |
GPM
(with minimal pressure loss & noise) |
GPH
(with minimal pressure loss & noise) |
GPM
(with significant pressure loss & noise) |
GPH
(with significant pressure loss & noise) |
| 1/2" |
.50-.60" |
.85" |
7 gpm |
420 gph |
14 gpm |
840 gph |
21 gpm |
1,260 gph |
| 3/4" |
.75-.85" |
1.06" |
11 gpm |
660 gph |
23 gpm |
1,410 gph |
36 gpm |
2,160 gph |
| 1" |
1.00-1.03" |
1.33" |
16 gpm |
960 gph |
37 gpm |
2,220 gph |
58 gpm |
3,510 gph |
| 1.25" |
1.25-1.36" |
1.67" |
25 gpm |
1,500 gph |
62 gpm |
3,750 gph |
100 gpm |
5,940 gph |
| 1.5" |
1.50-1.60" |
1.90" |
35 gpm |
2100 gph |
81 gpm |
4,830 gph |
126 gpm |
7,560 gph |
| 2" |
1.95-2.05" |
2.38" |
55 gpm |
3300 gph |
127 gpm |
7,650 gph |
200 gpm |
12,000 gph |
| 2.5" |
2.35-2.45" |
2.89" |
80 gpm |
4800 gph |
190 gpm |
11,400 gph |
300 gpm |
17,550 gph |
| 3" |
2.90-3.05" |
3.50" |
140 gpm |
8400 gph |
273 gpm |
16,350 gph |
425 gpm |
25,650 gph |
| 4" |
3.85-3.95" |
4.50" |
240 gpm |
14,400 gph |
480 gpm |
28,800 gph |
700 gpm |
42,000 gph |
| 5" |
4.95-5.05" |
5.563" |
380 gpm |
22,800 gph |
750 gpm |
45,000 gph |
1100 gpm |
66,000 gph |
| 6" |
5.85-5.95" |
6.61" |
550 gpm |
33,000 gph |
1100 gpm |
66,000 gph |
1700 gpm |
102,000 gph |
| 8" |
7.96" |
8.625" |
950 gpm |
57,000 gph |
1900 gpm |
114,000 gph |
2800 gpm |
168,000 gph |
Below is another data set we've run across. What is shows is how much flow you will get across a stainless metal ball valve of the length specified with a 1PSI pressure drop from one side of the valve to the other.
| Size (ID, inches) | Length (inches) | Flow (GPM) |
| 1/2 | 4.25 | 26 |
| 3/4 | 4.62 | 50 |
| 1 | 5.00 | 94 |
| 1-1/2 | 6.50 | 260 |
| 2 | 7.00 | 480 |
| 2-1/2 | 7.50 | 750 |
| 3 | 8.00 | 1300 |
| 4 | 9.00 | 2300 |
| 6 | 15.50 | 5400 |
Note: The data is for water through the valve only, and does not take into account the rest of the system. It does not give flow velocity, so there is some question as to the applicability of the data. The data comes from a book for industrial piping and probably assumes a massive pump, high flow velocities and metallic pipes. (Ie, where water hammer and noise are less of a concern than with PVC pipe.) As always, "you mileage may vary."
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GPM/GPH Flow based on PVC Pipe Size
In the chart to the left is a general guideline for how much liquid a pipe of specific size can flow in GPM (Gallons Per Minute) & GPH (Gallons Per Hour.) There are three columns. (Well there are really six, but each colum is shown in Gallons per minute, and then again as Gallons per Hour.) The first set of columns would be the minium you would expect for the pipe size shown using nothing but gravity to power the flow. The 2nd set of columns show what you can expect using an average pump with a pressure from 20 to 100psi. The 3rd set of columns is the peak, maximum would could get. This is a very general guide and is subject to many variables. Pressure, noise allowance, bends, fittings, viscosity, etc. affect how much liquid will flow through a pipe of given size. If you can accept more noise and have higher pressure, you can pump more. If you have a lot of bends and fittings you will flow less. The flow rates shown should not produce unacceptable noise, however, many variables affect noise, so this is no guarantee that the system will be noiseless. Sometimes experimentation is the only sure way to know if a system will be noisy or not. The flow rates shown are for water, with viscosity of 1. Higher viscosity liquids will flow less, lower viscosity liquids may flow more.
Note: One of the benefits of using Flex PVC pipe is being able to make long gradual bends instead of using fittings which will allow more flow with less noise, less back pressure, and less load on the pump. In other words, a more efficient system.
*"High Pressure" is a general and non-specific figure. What might be "high pressure" for 1/2" pipe (600psi) may not be "high pressure" for 2" pipe (280psi). There are just too many variables to consider to give a real world number. The fact of the matter is, on a pressurized system, the pump will dictate the flow and pressure as much as the pipe used. To achieve the flow figures in the peak column, it's assuming there are no bends and a short straight flow path. If your system has bends and T's, Wyes, etc, you should go to a larger pipe to achieve the flow desired. Also feed pressure effects the system. If the feed pressure is too low, you can get cavitation and you'll damage the pump and flow very little.
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