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71
tanks. Open the oxygen valve slightly and then wait while the high pressure
gauge on the regulator stops rising. Then open the valve fully, until it stops
turning. This is a back stop valve. Turning the valve all of the way out
prevents leakage through the packing of the valve.
Open the fuel valve also. Only open an acetylene valve one quarter
turn. This helps prevent the acetylene from being drawn off too quickly. If
acetylene 'bubbles' too rapidly from the acetone, it might become unstable.
Open the valve on a LPG tank out completely as on an oxygen tank and for
the same reasons.
If there are any leaks in the connections, regulators or torch, or any
other faults with the equipment, a safety hazard exists. The equipment should
not be used.
Never oil an oxygen regulator. It will cause a fire or explosion — solid
brass regulators can be blown apart from the force. Keep oxygen away from
all combustibles.
After this preparation, set the regulators at the desired pressure. For
acetylene, this should never be more than 103 kPa (15 lbf/in²). To prevent a
large yellow, sooty flame when first lighting the torch, open both the fuel and
the oxygen valves (more fuel than oxygen), and light a flame with a 'striker'
or by some other means. After the flame is adjusted to the proper size, open
the oxygen valve and adjust it to give the desired balance of fuel and oxygen.
Usually a neutral flame is used: this is a flame where the fuel and oxygen
supplied to the torch tip are both completely combined with each other. An
oxidizing flame has an excess of oxygen and a reducing flame has an excess
of fuel (carbon). An oxidising flame is used for cutting and a reducing flame
is used for annealing e.g. to soften steel sheet metal.
An acetylene flame (as is characteristic of most fuel/oxygen flames)
has two parts; the light blue to white colored inner cone and the blue colored
outer cone. The inner cone is where the acetylene and the oxygen combine.
The tip of this inner cone is the hottest part of the flame. The outer cone is
where hydrogen and carbon monoxide from the breakdown of the acetylene
and partial combustion of the inner cone combine with the oxygen in the
surrounding air and burns.
A neutral flame has a well defined inner cone. A reducing flame has a
feathery inner cone. An oxidizing flame has a smaller inner cone that is
sharply defined and is pale blue. The welder observes this while adjusting the
fuel and oxygen valves on the torch to get the correct balance for the job at
hand. There is also a difference in the noise the flame makes. Adjusting the
flame is not a hard thing to do after a little experience and practice.
The size of the flame can be adjusted to a limited extent by the valves
on the torch and by the regulator settings, but in the main it depends on the
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