Use the graph or tables below to determine the range of air leakage you can test with the Cobra using our standard orifice plates.

Note that the data is based on laboratory tests with short lengths of hard pipe attached to the duct leakage tester. Actual field performance will likely result in reduced performance due to: (1) amount of flexible duct used; (2) number of bends in flexible duct; (3) size of duct system; (4) line voltage. To account for flexible duct and 90 degree bends, use our program that takes these in-line losses into account.

12.5 mm Orifice Plate

System Static Pressure (Pa)Min Leakage with Cobra Tester (L/s)Max Leakage with Cobra Tester (L/s)
2500.54.7
5000.54.7
7500.54.3
10000.53.8
12500.53.5
15000.53.3
20000.51.9

25 mm Orifice Plate

System Static Pressure (Pa)Min Leakage with Cobra Tester (L/s)Max Leakage with Cobra Tester (L/s)
2504.221
5004.220
7504.218
10004.217
12504.215
15004.214
20004.29

50 mm Orifice Plate

System Static Pressure (Pa)Min Leakage with Cobra Tester (L/s)Max Leakage with Cobra Tester (L/s)
2501680
5001678
7501671
10001666
12501660
15001654
20001635

75 mm Orifice Plate

System AStatic Pressure (Pa)Min Leakage with Cobra Tester (L/s)Max Leakage with Cobra Tester (L/s)
25039198
50039194
75039184
100039177
125039157
150039137
20003992

100 mm Orifice Plate

System Static Pressure (Pa)Min Leakage with Cobra Tester (L/s)Max Leakage with Cobra Tester (L/s)
25083307
50083304
75083297
100083283
125083257
150083219
200083165

Min Leakage is the recommended minimum flow rate based on a 100 Pa pressure drop across the orifice plate. For example, approximately 39 L/s through the 75 mm orifice plate results in a 100 Pa pressure drop so 39 L/s is the recommended minimum leakage. Although it is possible to measure an orifice plate pressure differential lower than 100 Pa, the accuracy of the resulting flow rate is decreased. Unit of L/s is equal to liters per second.