990 CLD Autoline™ Leak Detector
DR
AFT 2/2/04
6-3
Facts about Leak Rates
Sizes of Leaks in
Man-Made joints
Studies indicate that almost all leaks at joints are about
5 x 10
-7
std cc/sec (about 1 cc/month) or larger. This is true
of ceramic-to-metal, plastic-to-metal seals, welded, soldered
and brazed joints. Some long-path leaks may be slightly smaller.
Diffusion of helium through glass may be as high as 10
-8
std cc/sec
per square centimeter of surface area.
Variation in Leak Sizes Leaks unintentionally
built-in
at joints during manufacture
may vary from hour to hour and day to day. Breathing on a
10
-6
std cc/sec leak provides enough moisture to close it
temporarily, perhaps for several days. Atmospheric particles
can close a leak of this size. Never depend on an
accidentally
made
leak to remain constant. Manufacturing standard leaks
for calibration purposes requires special techniques.
Visualizing Leaks in
Everyday Terms
10
−
5
std cc/sec:
10
−
7
std cc/sec:
Approximately 1 cc/day
Approximately 3 cc/year
Audible or Visual
Detection by
Observer
Bubbles rising in water: 10
−
4
std cc/sec or larger
Audible Leaks:
10
−
1
std cc/sec or larger
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