[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anything from zero to 1,800 pounds, and will vary as the gas is withdrawn,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. Attached to the diaphragm is a sleeve or an arm tipped
with a small piece of fibre, the fibre being placed so that it is directly
opposite the small hole through which the gas entered the diaphragm
chamber. The slight movement of the diaphragm draws the fibre tightly over
the small opening through which the gas is entering, with the result that
further flow is prevented.

Against the opposite side of the diaphragm is the end of a plunger. This
plunger is pressed against the diaphragm by a coiled spring. The tension on
the coiled spring is controlled by the operator through a threaded spindle
ending in a wing or milled nut on the outside of the regulator body.
Screwing in on the nut causes the tension on the spring to increase, with a
consequent increase of pressure on the side of the diaphragm opposite to
that on which the gas acts. Inasmuch as the gas pressure acted to close the