How to Calculate the Flow If I Know the Pipe ID & the Water Pressure
- 1). Refer to the first link in "Resources" to find the thickness of the pipe's wall. A schedule 10 pipe rated at 8 inches, for instance, has a wall thickness of 0.148 inches.
- 2). Refer to the same table to find the pipe's outer diameter. The schedule 10 pipe rated at 8 inches has an outer diameter of 8.625 inches.
- 3). Divide the outer diameter by 2: 8.625 / 2 = 4.313 inches.
- 4). Subtract the wall thickness from this answer: 4.313 - 0.148 = 4.17 inches. This is the pipe radius.
- 5). Divide the radius by 39.4 to convert it to meters: 4.17 / 39.4 = 0.106 meters.
- 6). Square the radius: 0.106 ^ 2 = 0.0112.
- 7). Multiply this answer by the water pressure drop. If the pressure drops, for instance, by 80,000 Pascals: 0.0112 x 80,000 = 896.
- 8). Multiply the answer to Step 6 by pi: 0.0112 x 3.142 = 0.0352.
- 9). Multiply the answers to Steps 8 and 7: 0.0352 x 896 = 31.54.
- 10
Multiply the pipe's length by 8. With a length, for instance of 100 meters: 100 x 8 = 800. - 11
Multiply this answer by 0.01, the viscosity of water: 800 x 0.01 = 8. - 12
Divide the answer to Step 9 by the answer to Step 11: 31.54 / 8 = approximately 2.9. This is the pipe's flow rate in cubic meters per second.
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