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Shown below are
the differences between bowed and buldged cylinders,
along with the reasons for inspecting a cylinder with a straight
edge.
Bowed Cylinder
A bowed cylinder
will exhibit an area of the sidewall that is convexed (curved
outward) and also an area, 180° opposite the convex side, that is
concaved (curved inward). A bowed cylinder is sometimes identified
as exhibiting a "banana effect". A bowed cylinder can be verified
by identifying the convexed, humped, side of the cylinder with
a straight edge, then rotating the cylinder 180º and verifying this
side of the cylinder is concaved, recessed from the straight
edge.
A bowed cylinder sometimes occurs due to variations in the manufacturing process.
For a standard 3000
psi, 80 cuft scuba cylinder, Catalina Cylinders considers a bow measured on
the concave side of the cylinder acceptable if .085" or less.
A Bulged Cylinder
A bulged cylinder
will exhibit at least some area of its sidewall being convexed
(curved outward). It is possible for the entire sidewall
of the cylinder to be bulged and curved outward. The bulge
is readily identified as a hump in the sidewall of the cylinder
when checking with a straight edge. A bulged cylinder indicates
that the metal has yielded and is no longer safe for use.
A bulged cylinder should be condemned.
It is very rare for a cylinder to be bulged. A cylinder that is bulged has usually been overheated or overfilled.
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