Abstract: A leak detector has a dual sensitivity due to two thresholds, a first established by a standard leak of the test gas representing the smallest leak to be detected, and the second as a fraction of the first one. A variable autozero level is used to compensate for background but is limited in its range to prevent masking of the leak by the autozero level. When measured gas concentration in excess of the autozero level exceeds the second threshold, the autozero value is held at a fixed value and an annuciator produces a signal as a function of the concentration so that the maximum concentration and the leak site can be found. When the leak site is found, the operator selects the first threshold for comparison with the gas concentration in excess of the held autozero value to determine whether the leak exceeds the rejection level.

Abstract: A method of self-pressurizing a piston-and-rod type hydraulic damper by means of an internally generated gas including the steps of positioning in the damper a volatile condensed phase of the pressurizing gas contained under pressure within a rupturable capsule and replacing the capsule after the damper is filled and sealed. Heat softenable capsules containing Freon, or the like, are disclosed.