Measuring and testing – With fluid pressure – Leakage
Patent
1982-12-16
1984-10-23
Goldberg, Gerald
Measuring and testing
With fluid pressure
Leakage
G01N 320
Patent
active
044779860
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of, and apparatus for, detecting leaks. It is particularly, though not exclusively, concerned with detecting leaks that arise in the manufacture of assembled vehicles in the course of production.
According to one aspect of the present invention, there is provided a method of detecting the presence of a leakage path leading to the surface of a fabrication comprising the steps of: fabrication; a leakage path leading to the surface; outflow of air from the sampler, the curtain serving with the sampler and the surface to define a sampling volume; curtain to stabalise the air curtain and to maintain the gas pressure in the sampling volume at a level such that gas adjacent the surface passes to the sampler; probe incorporated in the sampler; and is present or absent.
According to a second aspect of the present invention there is provided an apparatus for detection of a leakage path leading to the surface of a fabrication, the apparatus comprising a sampler which has: withdrawn from a sampling volume adjacent an end of the body; in the sample; said end of the body; body to determine the relative axial positions thereof; and the continuous gap to establish an air curtain around the sampling volume.
An exemplary embodiment of the invention will now be described with reference to the accompanying drawings in which:
FIG. 1 is a sectional view of a sampler according to this invention; and
FIGS. 2 to 4 show the sampler of FIG. 1 in use.
FIG. 1 shows a shrouded sampler 10 with a body 11 disposed concentrically within a shroud 12 to define an annular gap 17 therebetween. The position of the shroud 12 is adjustable with respect to the body 11 to permit variation, where necessary, in the setting of a margin D between the end of the shroud 12 and an end face 13 of the body 11. In use, values of D of up to 25 mm have been used. The body 11 is circular in cross-section and has extending through it a probe tube 14 by means of which samples of gas in the vicinity of the end face 13 can be withdrawn for passage to a gas sensor 18. The gas sensor 18 is a mass spectrometer adjusted to respond to traces of helium. A plenum chamber 15 between the body 11 and the shroud 12 is supplied with air under pressure by an inlet manifold 16. The passage of air through annular gap 17 from the chamber 15 provides an air curtain C (see FIG. 2) around the end face 13 the use of which will be described hereafter in connection with FIGS. 2 to 4. Gas pressure in the vicinity of the end face 13 is controlled by regulating the rate of diffusion from the air curtain but can also be controlled by means of a vacuum source acting through a duct 19 and a passage 20 in the body 11. The pressure in this area is maintained at a level lower than that causing the gas to be driven along any leak path in a fabrication under test to the vicinity of end face 13. A flexible line 21 couples the sampler 10 to a work station which houses the gas sensor 18.
FIGS. 2 to 4 show the use of the sensor shown in FIG. 1 for detecting a leak in a car body. The car body is generally shown by the designation B and a leak path, which may for example be through a window or door seal, is shown by the designation L. The sampler is initially mounted adjacent the car body B and an air curtain C is established by pressurising air in the chamber 15 so that air is driven out of the annular gap 17. The air curtain C, the end face 13 and the upper surface of the car body B serve to define a sampling volume S. The sampler is driven across the car body surface in the direction shown by arrow 22. FIG. 2 shows the air curtain C about to pass over the upper end of a leak path L in the body B. In this position, the leak path L does not communicate with the sampling volume S.
Prior to the application of the sampler, helium gas was introduced into the car body and diffused thoughout the interior thereof by a fan-type system. The interior is slightly pressurised to ensure that the resulting mixture of air and helium within the car body passes along any leak paths, s
REFERENCES:
Rogal, Jet Probe of a Halide Leak Detector, Nov. 1976.
Marshall Peter E. G.
Piper Francis R.
Wilson John F.
BL Technology Limited
Goldberg Gerald
Williams Hezron
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