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