7.2.3 Bubbler devices
Figure 4.31 shows the two different types of bubbler which are used for tube leak detection.
Figure 4.31 (a), the conventional bubbler, monitors the flow of air through a hole when the leaking tube is under vacuum. The method will detect leaks down to 175 ml/h, and an arrangement is adopted where 10 tubes are monitored simultaneously, enabling 700 tubes/hour to be checked. Two operators are required for this method which is suitable for off-load use providing a vacuum of 330 mbar can be obtained.
Figure 4.31 (b), the MEL bubbler, is similar in prin¬ciple to the conventional bubbler except that the suspect tube is evacuated with atmospheric pressure on the outside of the tube. This method can locate leakage rates of only 35 ml/h, the test rate being up to 200 tubes/hour.