Isolator Leak Rate Calculator (ISO 10648-2)
Turn a pressure decay reading into an hourly leak rate and ISO 10648-2 leak-tightness class, with temperature correction. Enter your start and end pressure, the measurement time and the chamber temperature.
Engineering estimate only. Confirm by testing and validation for your equipment and load.
How the calculation works
ISO 10648-2 classifies containment enclosures by their hourly leak rate Tf: the volume of gas that leaks in one hour divided by the volume of the enclosure. Because the enclosure volume is fixed, the fraction of gas lost (or gained) during a pressure decay test can be found from the ideal gas law using absolute pressures and absolute temperatures:
P = absolute pressure (atmospheric + gauge), T = absolute temperature in K, t = measurement time in minutes, Tf in h−1
The result is compared with the class limits:
| ISO 10648-2 class | Hourly leak rate Tf |
|---|---|
| Class 1 | ≤ 5 × 10−4 h−1 |
| Class 2 | ≤ 2.5 × 10−3 h−1 |
| Class 3 | ≤ 10−2 h−1 |
| Class 4 | ≤ 10−1 h−1 |
Why temperature matters so much
At around 20 °C, a change of 0.1 °C in the chamber air changes the absolute pressure by roughly 35 Pa. Over a 30-minute test, Class 1 allows a drop of only about 25 Pa. A chamber that is cooling slightly can make a leaking isolator look tight under positive pressure; one that is warming can make a tight isolator fail. That is why the calculator asks for the temperature at both ends, and why a stabilisation period before the measurement is essential.
Limits of this calculator
- It assumes the enclosure volume does not change. Gloves and flexible panels that move during the test add error.
- Gauge readings are relative to atmospheric pressure. A change in barometric pressure during the test is not corrected here.
- It is an engineering check, not a qualification record. Formal testing follows the method, test pressure and acceptance criteria in your URS and protocol.
For the full method see isolator leak testing by pressure decay; gloves are tested separately — see isolator glove integrity testing.
Common questions
How do I calculate isolator leak rate from a pressure decay test?
Convert the start and end gauge pressures to absolute pressure, apply the ideal gas law with the start and end temperatures, take the fraction of gas lost and scale it to one hour: Tf = |1 − (P2·T1)/(P1·T2)| × 60 / t, with t in minutes.
What leak rate does ISO 10648-2 Class 2 allow?
Class 2 allows an hourly leak rate up to 2.5 × 10⁻³ h⁻¹. Over a 30-minute test at about 500 Pa this is a drop of roughly 127 Pa.
Why does the calculator need temperature?
Because a temperature change shifts the pressure of the enclosed air. A 0.1 °C change is about 35 Pa, which is larger than the whole Class 1 allowance over 30 minutes.
Can I use the calculator for a negative pressure test?
Yes. Enter the gauge pressures as negative values. The calculator uses the magnitude of the change in gas quantity, so the result is valid for both positive and negative tests.
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