According to DIN EN 1330, the unit [Pa*m³/s] is defined for determining the leak rate.
1 Pa*m³/s corresponds to a pressure change of one Pa in a closed volume of one m³ within one second.
In practice, however, the units [mbar*l/s] or [cm³/min] are more commonly used.
The conversion from [Pa*m³/s] to [mbar*l/s] is a simple unit conversion:
100 Pa = 1 mbar
1 m³ = 1,000 l
Therefore,
1 mbar *l/s = 0.1 Pa*m³/s
With a leak rate of 1 mbar*l/s, the pressure in one liter of volume therefore changes by 1 mbar within one second.
For example, from a volume of 1,000 cm³ under 1,000 mbar pressure, 1 Ncm³ flows out per second. (Ncm³ is 1 cm³ under standard conditions, i.e., at 1013.25 mbar air pressure / 0°C)
Therefore, under manufacturing conditions, it approximately holds:
1 mbar*l/s corresponds to 1 cm³/s or 60 cm³/min
A leak rate of 1 x 10-3 mbar*l/s therefore corresponds to a volume flow of 0.06 cm³/min.
If this value is now compared with an air-under-water test, the volume of the rising air bubbles must be calculated.
An air bubble with a diameter of 1 mm has a volume of 0.52 mm³ or 0.00052 cm³.
With a leak rate of 10-3 mbar*l/s, 114 air bubbles with a 1 mm diameter therefore rise per minute in a liquid.
If the diameter of the air bubbles is 2 mm, however, an air bubble has a volume of 4.16 mm³, and their number reduces to 14.4.
It should be noted, however, that due to the water hardnesses and surface tensions common in Germany, the diameter of a "real" air bubble in an air-under-water test is even more likely to be 2.5 to 3 mm.
