enters the mixing chamber, being driven by its own pressure.

The acetylene enters the head in an annular space surrounding the oxygen
tube. The space between oxygen jet and mixing chamber opening is at one end
of this acetylene space and the stream of oxygen seizes the acetylene and
under the injector action draws it into the mixing chamber, it being
necessary only to have a sufficient supply of acetylene flowing into the
head to allow the oxygen to draw the required proportion for a proper
mixture.

The volume of gas drawn into the mixing chamber depends on the size of the
injector openings and the pressure of the oxygen. In practice the oxygen
pressure is not altered to produce different sized flames, but a new nozzle
is substituted which is designed to give the required flame. Each nozzle
carries its own injector, so that the design is always suited to the
conditions. While torches are made having the injector as a permanent part
of the torch body, the replaceable nozzle is more commonly used because it
makes the one torch suitable for a large range of work and a large number
of different sized flames. With the replaceable head a definite pressure of
oxygen is required for the size being used, this pressure being the one for
which the injector and corresponding mixing chamber were designed in
producing the correct mixture.

_Adjustable Injectors._-Another form of low pressure torch operates on
the injector principle, but the injector itself is a permanent part of the
torch, the nozzle only being changed for different sizes of work and flame.
The injector is placed in or near the handle and its opening is the largest
required by any work that can be handled by this particular torch. The
opening through the tip of the injector through which the oxygen issues on
its way to the mixing chamber may be wholly or partly closed by a needle