Example: Integral leak test on a heat-exchanger

Heat exchanger
Volumes around the tube:
Volume in the tubes:
Effective pumping speed
3.750 l
3.176 l
17 l/s

The effective pumping speed is the speed at the flange A of the heat exchanger (total pumping speed of the two pumps, reduced by the flow resistance of the pumping line).

The response time in this case is:

\tau = \frac{3760 \, l}{17 \, l/s} = 220,6 sec = 3 \, min \, 40,6 \, sec

For the leak rate signal to reach almost its end value, a waiting time of 5 time constants is recommended. (see the following table). Therefore, after the volume under the foils is filled with 100% helium, a waiting time of around 18 minutes and 23 seconds is necessary, before the leak rate reading can be taken.