Melting of this
plug allows the gas to exert its pressure against a thin copper diaphragm,
this diaphragm bursting under the gas pressure and allowing the oxygen to
escape into the air.
The hand wheel and upper end of the valve mechanism are protected during
shipment by a large steel cap which covers them when screwed on to the end
of the cylinder. This cap should always be in place when tanks are received
from the makers or returned to them.
[Illustration: Figure 14.--Regulating Valve]
_Regulating Valves._--While the pressure in the gas containers may be
anything from zero to 1,800 pounds, and will vary as the gas is withdrawn,
the pressure of the gas admitted to the torch must be held steady and at a
definite point. This is accomplished by various forms of automatic
regulating valves, which, while they differ somewhat in details of
construction, all operate on the same principle.
The regulator body (Figure 14) carries a union which attaches to the side
outlet on the oxygen tank valve. The gas passes through this union,
following an opening which leads to a large gauge which registers the
pressure on the oxygen remaining in the tank and also to a very small
opening in the end of a tube. The gas passes through this opening and into
the interior of the regulator body. Inside of the body is a metal or rubber
diaphragm placed so that the pressure of the incoming gas causes it to
bulge slightly.
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