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Compressed Air Discharge through an Orifice
 

The following table gives the discharge values expressed as a volumetric flow in litres per second (l/s) Free Air Delivered (F.A.D.). Note that this table is prepared for a downstream pressure of 1 bar abs.

Strictly the figures will depend on the type orifice, (rounded or sharp edges) but they can be generalised for the purpose of analysing the flow through any valve or control device.

This table is based on a 100% coefficient of flow. For well rounded entrance, multiply values by 0.97 and for sharp edged orifice multiply by 0.65 for approximate results.

Gauge pressure before orifice in bar Diameter of Orifice (mm)
0.5 1 2 3 4 5 7 10 15 20 25
Discharge of air in litres per second at 1 bar abs. and 15°C
0.5 0.054 0.217 0.869 1.956 3.477 5.433 10.65 21.73 48.90 86.83 135.8
1.0 0.076 0.303 1.213 2.729 4.851 7.579 14.86 30.32 68.21 121.3 189.5
2.0 0.114 0.455 1.819 4.093 7.276 11.37 22.28 45.48 102.3 181.9 284.2
3.0 0.152 0.606 2.425 5.457 9.702 15.16 29.71 60.64 136.4 242.5 379.0
4.0 0.189 0.758 3.032 6.821 12.13 18.95 37.14 75.79 170.5 303.2 475.5
5.0 0.227 0.910 3.638 8.186 14.55 22.73 44.57 90.59 204.6 363.8 568.5
6.0 0.265 1.061 4.244 9.550 19.98 26.53 51.99 106.1 238.8 424.4 663.2
7.0 0.303 1.213 4.851 10.91 20.40 30.32 59.42 121.3 272.9 485.1 757.9
8.0 0.341 1.364 5.457 12.28 21.83 34.11 66.85 136.4 307.0 545.7 852.7
9.0 0.379 1.516 6.063 13.64 24.25 37.90 74.28 151.6 341.1 606.3 947.4
10.0 0.417 1.667 6.670 15.01 26.68 41.69 81.71 166.7 375.2 667.0 1042
12.0 0.493 1.971 7.882 17.74 31.53 49.27 96.56 197.1 443.4 788.2 1232
15 0.606 2.426 9.702 21.83 38.81 60.64 118.8 242.6 545.7 970.2 1516
20 0.796 3.183 12.73 28.65 50.93 79.58 156.0 318.3 716.3 1273 1990

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Duncan Rogers (Engineering) Ltd, 396 Hillington Road, Glasgow, G52 4BL  Scotland

Tel: +44 (0) 141 882 6211   Fax: +44 (0) 141 882 5818   Email: info@duncanrogers.com