Coefficient of Discharge for Sharp-edged Orifices.
| Head in ft. | Form of Orifice. | |||||||
| Circular. | Square. | Rectangular Ratio of Sides 4:1 | Rectangular Ratio of Sides 16:1 | Tri- angular. | ||||
| Sides Vertical. | Diagonal Vertical. | Long Sides Vertical. | Long Sides hori- zontal. | Long Sides Vertical. | Long Sides Hori- zontal. | |||
| 1 | .620 | .627 | .628 | .642 | .643 | .663 | .664 | .636 |
| 2 | .613 | .620 | .628 | .634 | .636 | .650 | .651 | .628 |
| 4 | .608 | .616 | .618 | .628 | .629 | .641 | .642 | .623 |
| 6 | .607 | .614 | .616 | .626 | .627 | .637 | .637 | .620 |
| 8 | .606 | .613 | .614 | .623 | .625 | .634 | .635 | .619 |
| 10 | .605 | .612 | .613 | .622 | .624 | .632 | .633 | .618 |
| 12 | .604 | .611 | .612 | .622 | .623 | .631 | .631 | .618 |
| 14 | .604 | .610 | .612 | .621 | .622 | .630 | .630 | .618 |
| 16 | .603 | .610 | .611 | .620 | .622 | .630 | .630 | .617 |
| 18 | .603 | .610 | .611 | .620 | .621 | .630 | .629 | .616 |
| 20 | .603 | .609 | .611 | .620 | .621 | .629 | .628 | .616 |
The orifice was 0.196 sq. in. area and the reductions were made with g = 32.176 the value for Montreal. The value of the coefficient appears to increase as (perimeter) / (area) increases. It decreases as the head increases. It decreases a little as the size of the orifice is greater.
Very careful experiments by J. G. Mair (Proc. Inst. Civ. Eng. lxxxiv.) on the discharge from circular orifices gave the results shown on top of next column.
The edges of the orifices were got up with scrapers to a sharp square edge. The coefficients generally fall as the head increases and as the diameter increases. Professor W. C. Unwin found that the results agree with the formula
c = 0.6075 + 0.0098 / √ h − 0.0037d,
where h is in feet and d in inches.
Coefficients of Discharge from Circular Orifices. Temperature 51° to 55°.
| Head in feet h. | Diameters of Orifices in Inches (d). | ||||||||
| 1 | 11⁄4 | 11⁄2 | 13⁄4 | 2 | 21⁄4 | 21⁄2 | 23⁄4 | 3 | |
| Coefficients (c). | |||||||||
| .75 | .616 | .614 | .616 | .610 | .616 | .612 | .607 | .607 | .609 |
| 1.0 | .613 | .612 | .612 | .611 | .612 | .611 | .604 | .608 | .609 |
| 1.25 | .613 | .614 | .610 | .608 | .612 | .608 | .605 | .605 | .606 |
| 1.50 | .610 | .612 | .611 | .606 | .610 | .607 | .603 | .607 | .605 |
| 1.75 | .612 | .611 | .611 | .605 | .611 | .605 | .604 | .607 | .605 |
| 2.00 | .609 | .613 | .609 | .606 | .609 | .606 | .604 | .604 | .605 |
The following table, compiled by J. T. Fanning (Treatise on Water Supply Engineering), gives values for rectangular orifices in vertical plane surfaces, the head being measured, not immediately over the orifice, where the surface is depressed, but to the still-water surface at some distance from the orifice. The values were obtained by graphic interpolation, all the most reliable experiments being plotted and curves drawn so as to average the discrepancies.