Heating or cooling of a vacuum seal enables testing over a wide temperature range.

The figure schematically depicts a portable microleak-detection system that has been built especially for use in testing hydrogen tanks made of polymer-matrix composite materials. (As used here, “microleak” signifies a leak that is too small to be detectable by the simple soap-bubble technique.) The system can also be used to test for microleaks in tanks that are made of other materials and that contain gases other than hydrogen. Results of calibration tests have shown that measurement errors are less than 10 percent for leak rates ranging from 0.3 to 200 cm³/min.

The Portable Microleak-Detection System includes components in common with prior microleak-detectionsystems, plus a seal-heating/cooling subsystem that enables testing over a wide temperature range.

The flexibility of the chamber makes it adaptable to test objects having a variety of simple or complex shapes. The flexible vacuum chamber includes an aluminized polyethylene terephthalate vacuum membrane that is sealed to the outer surface of the test object by a flexible, adhesive seal material. A scrim is placed between the inner surface of the membrane and the outer surface of the test object to maintain a gap to accommodate the flow of any leaking gas. A capillary tube that passes through the seal connects the gap volume with the plumbing that leads to the mass spectrometer, the vacuum pump, and a control volume described next.