virtual leak

virtual leak

[′vər·chə·wəl ′lēk]
(engineering)
The semblance of the vacuum system leak caused by a gradual desorptive release of gas at a rate which cannot be accurately predicted.
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References in periodicals archive ?
The IR radiation will heat the internal surfaces and desorb the adsorbed contaminants, especially water vapor, and provide enough heat to drive contaminants out of the surface oxide layer, pores, cracks, and virtual leak traps.
For example, a blind-tapped-hole virtual leak can be relieved by providing a drilled-through hole along the screw's longitudinal axis.
The ball valve has never been considered a good choice because of inherent virtual leak possibilities, stem leaks, and gas entrapment.
2] filling virtual leak voids and barring water diffusion into those voids due to the small [N.
2] instead of air is more a function of pre-filling the virtual leak voids with water-free gas.
In this situation, a leaking front seat could create a virtual leak.
A virtual leak is caused by entrapped air within the vacuum system, commonly between two mating metal surfaces that are not welded or brazed.
Thermal effects create virtual leaks that must be compensated for by test methods to achieve the failsafe leak test standard.
Pockets of gas trapped within the confines of the vacuum chamber are usually referred to as virtual leaks, but this term is used only because they can easily be mistaken for real leaks.
Internal virtual leaks also provide a useful example in that pockets of active gas can result in gas-process reactions that are never detected by the gauges.
Although this problem is avoided with UV energy, which will flood the whole chamber, the UV energy will not penetrate into the trapped volume of virtual leaks or reach the surfaces of O-rings recessed between flanges.

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