A practical example from tires

In the following simple example, we can calculate the leak in an automotive tire when we lose 2 PSI or 0.136092 atmosphere in 60 days. (In this example, we consider that the volume of the tire does not vary/diminish because of the pressure).

With the tire having a volume of 30 liters and a pressure of 32 PSIG or 2.177471 atmosphere, we calculate that the tire contains 30 * 2.177471 = 65.32413 NL.

A loss of 2 PSI or 0.136092 atmosphere equals a volumetric loss of 30 * 0.136092 = 4.08276 NL equals 4082.76 Normal Cubic Centimeter.

60 days converts to 5184000 seconds. So we can now express this leak in atm.cc/sec being 4082.76 / 5184000 = 0.00078757 atm.cc/sec or scientifically notated as 7.8757E-4 atm.cc/sec. This is equal to 7.95 * 10-4 mbar.l/s or 0.805 mm3/s

(The unit mm3/s is generally used for larger leaks and is most common in the automotive industry. The unit g/year is often used for smaller leak rates and is widely used in the refrigeration industry).


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