Skimmer Sizing

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.

Technical Sizing Instructions

To read “Determining the Skimmer Size and the Required Orifice for the Faircloth Skimmer®   Surface Drain” click here .

Online Sizing Calculator

Detailed instructions can be found here .

Instructions: 

  1. Download the Sizing Calculator. Microsoft Excel is required.
  2. Enter Volume (in cubic feet) of basin to be drained and Number of Days in the green boxes
  3. Hit ENTER to run the spread sheet. The skimmer size and the orifice radius and diameter will appear in the blue box*. 
    *Caution  :   This 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. Therefore it is recommended that the following chart be used together with the spread sheet.

Basin Volume Estimator  

If you do not know the basin’s volume but know the dimensions and depth of a square or rectangular basin, enter the dimensions in the Volume Estimator portion of the SIZING CALCULATOR.   

FLOW CAPACITIES (in Cu. Ft.) 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

Important note: The orifice sizing chart in the Pennsylvania Erosion Control Manual DOES NOT APPLY to Faircloth Skimmer® surface drains. It will give the wrong size skimmer. Please use these instructions to choose the size skimmer required for the basin volume and the orifice size.