Calculate Faircloth Skimmer® Size & Print Detail Drawing
Use the following calculator to create a detail drawing in PDF format. You can then print or save the PDF document and easily add it to your plan set. Note: You can calculate multiple skimmer basins with this tool! — simply click “Add Row” to add a basin to the detail.
Calculate Faircloth Skimmer® Size
Basin Volume Calculator
If you do not know the basin’s volume but you do know the dimensions and depth of a square or rectangular basin, use this calculator to estimate the volume.
Important!
The calculator does not take into consideration Common Sense. For example, if the volume entered is even one cubic foot greater that the maximum calculated capacity of a skimmer the next larger size will be given as the answer.
In reality, a reasonable judgment would be that the smaller size is adequate given the room for error in the assumptions that go along with the design and sizing process.
For example: using the entire volume of the basin to determine the skimmer size assumes that the basin fills during every rain event, which is usually not the case (therefore, the basin will drain somewhat quicker); it also assumes inflow to the basin stops when the basin is full, which may not be the case (inflow may continue, lengthening the drain time); or another rain event may occur before the basin drains.
Therefore it is recommended that the following flow capacities chart be used together with the calculator.
FLOW CAPACITIES (in ft 3 ) FOR THE Faircloth Skimmer®
| Skimmer size | 1.5″ | 2″ | 2.5″ | 3″ | 4″ | 5″ | 6″ | 8″ |
|---|---|---|---|---|---|---|---|---|
| 24 hours | 1,728 | 3,283 | 6,234 | 9,774 | 20,109 | 32,832 | 51,840 | 97,978 |
| 2 day | 3,456 | 6,566 | 12,468 | 19,548 | 40,218 | 65,664 | 103,680 | 195,956 |
| 3 day | 5,184 | 9,849 | 18,702 | 29,322 | 60,327 | 98,496 | 155,520 | 293,934 |
| 4 day | 6,912 | 13,132 | 24,936 | 39,096 | 80,436 | 131,328 | 207,360 | 391,912 |
| 5 day | 8,640 | 16,415 | 31,170 | 48,870 | 100,545 | 164,160 | 259,200 | 489,890 |
| 6 day | 10,368 | 19,698 | 37,404 | 58,644 | 120,654 | 196,992 | 311,040 | 587,868 |
| 7 day | 12,096 | 22,981 | 43,638 | 68,418 | 140,763 | 229,824 | 362,880 | 685,846 |
DETERMINING SKIMMER SIZE
- Eight sizes available, ranging from 1½” for small sediment traps to 8” for very large basins.
- Size refers to the maximum diameter of the inlet. For example, a 4” Faircloth Skimmer® has a 4” maximum orifice size.
- Each Faircloth Skimmer® includes a plug and adjustable cutter for making an orifice (hole) smaller than the inlet to customize the flow rate for the particular basin.
Method Used
The flow rates used in the calculator and listed in the chart are theoretical rates calculated using the orifice equation and the head on the inlet for each size skimmer. (Note that the head is different for each size skimmer.)
Also, the head may vary slightly when the skimmer is in use, plus or minus, depending upon the depth of water and the position of the skimmer. The actual flow rate for the installed skimmer may be slightly less than calculated, especially when the barrel has a flat or low slope.
Any variation in flow rate is considered insignificant enough to appreciably affect the drain time considering the number of variables involved. Therefore, the theoretical rates are used to simplify the orifice sizing process.
The calculation is rounded to the nearest 10th of an inch because that is as close as the cutter can be adjusted and the orifice cut.