Helium, Hydrogen
and sensitivity
Because the Hydrogen must be used mixed at 5 % concentration with
an inert gas to be safe, the sensitivity of the test drops by a factor of
20 compared to 100 % Hydrogen concentration.
Theoretical example
Reject point of the part to be tested: 5 x10
-5
mbar.l/s.
H
2
concentration: 100 %
Leak to be found: 5 x10
-5
mbar.l/s.
H
2
concentration: 10 %
Leak to be found: 5 x10
-6
mbar.l/s.
H
2
concentration: 5 %
Leak to be found: 2,5 x10
-6
mbar.l/s.
Air conditioning example
The working pressure of the system to be tested is 50 bar and the
allowed loss is 2,5 g per year.
If the system is filled with R410 refrigerant gas, the maximum allowed
leak in R410 at 50 bars is 2,63 x10
-5
mbar.l/s.
Calculation for equivalent leak with substitute gas
Pressure test: 8 bar, gas concentration 100 %
Equivalent leak in Hydrogen (H
2
): 3,32 x 10
-5
mbar.l/s.
Equivalent leak in Helium (He): 1,66 x10
-5
mbar.l/s.
Because Hydrogen is not a safe gas, the maximum concentration of
H2 in N2 is 5 % to be non-flammable.
With a such concentration, the leak to be found becomes 20 times
lower at 1,66 x10
-6
mbar.l/s.
Conclusion
To control an air conditioning system and validate with a substitute
gas that the system is tight you need for the Hydrogen method a leak
detector 10 times more sensitive than a Helium leak detector.
To compare sensitivity between Helium and Hydrogen, you have to
compared the following information:
Leak to be found Gas used Leak to be displayed
5.10
-5
mbar.l/s Helium 5.10
-5
mbar.l/s
Hydrogen mixture
95 % N2 + 5 % H2
5.10
-6
mbar.l/s
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