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 (cmh)Max Leakage with Cobra Tester (cmh)
2501.717
5001.713.6
7501.713.6
10001.711.9
12501.711.9
15001.710.2
20001.75.1

25 mm Orifice Plate

System Static Pressure (pa)Min Leakage (cmh)Max Leakage with Cobra Tester (cmh)
2501565
5001562
7501556
10001551
12501545
15001536
20001516

50 mm Orifice Plate

System Static Pressure (Pa)Min Leakage (cmh)Max Leakage with Cobra Tester (cmh)
25055265
50055255
75055250
100055230
125055215
150055170
20005560

75 mm Orifice Plate

System Static Pressure (Pa)Min Leakage (cmh)Max Leakage with Cobra Tester (cmh)
250140705
500140700
750140665
1000140640
1250140580
1500140495
2000140195

100 mm Orifice Plate

System Static Pressure (Pa)Min Leakage (cmh)Max Leakage with Cobra Tester (cmh)
2502951115
5002951095
7502951070
10002951020
1250295925
1500295790
2000295340

Min Leakage is the recommended minimum flow rate based on a 100 Pa pressure drop across the orifice plate. For example, approximately 140 cmh through the 75 mm orifice plate results in a 100 Pa so 140 cmh 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 cmh is equal to cubic meters per hour.