21
on the fuel again and proceed as before. We have divided the subject of "Backfiring" into two general classes
.
It may
happen when the fire is just coming on, or it may happen when the fire is shutting off, or as under the heads of B and
C on the chart, it may happen either way.
WHEN FIRE IS COMING ON
Any cracks in the burner grate are pretty sure to cause backfire. A backfire is apt to occur accompanied by
slight explosions as the gas ignites back to the nozzle. If there is a suspicion that the burner is cracked, It is best to
take it down and examine it carefully. The crack can be plastered over with fire clay, allowing it to dry, or it can be
dried quickly by the flame of a blowtorch. In case the burner is taken down it is a good thing to see that it is perfectly
clean and that there is no mud or loose dirt contained in the base of the burner.
Sometimes a backfire will occur in firing up, if the raw fuel is
turned on too rapidly. When first admitting
fuel to the burner, care should be exercised that the vaporizer is
hot enough to vaporize the fuel properly. For the first
thirty seconds the fuel should be turned on and off at intervals of about two seconds, preventing too great a rush
through the comparatively cold vaporizer. It is characteristic of the Bunsen system that the richer the mixture the
lower the flame lies upon the burner. If the fuel is too "raw", the mixture is so rich that the flame lies directly on the
burner slots, giving a good chance for the ignition to occur below the grate, thus causing a backfire.
If the pilot light is turned too low, the vaporizer may not be kept sufficiently hot to vaporize properly, giving
the effect of turning on the raw fuel too fast. Again the gas may accumulate around the back side of the burner before
the low pilot light flame reaches it, and when it ignites it may puff back through the burner grate and catch on the
vaporizer nozzle.
If there is any leaking around the edge of the burner, especially on some of the older model cars, the flame
from the inside may shoot out and ignite the gas at the vaporizer tip.
If too much air is being admitted through the mixing tube, giving a high fluffy fire, the mixture may be so
thin that it will not ignite rapidly and accumulate enough, so that when ignition does occur it may puff back and cause
the gas to catch at the vaporizer tip.
A split vaporizer may cause a backfire, either coming on or shutting off. To cause this the split would
probably be on the lower side of the vaporizer. The jet of flame, by striking the burner slots, might force through
enough to ignite the gas below. A split vaporizer is usually caused by being overheated or partly clogged and
overheated at the same time. The new style vaporizers issued by the White Co. in the fall of 1908 have almost entirely
eliminated any troubles from clogging or splitting. These vaporizers are very light, are perfectly smooth inside, and
heat very quickly.
A slow gas leak through the flow motor fuel valve or the hand valve may accumulate the gas at the back side
of the burner, which may cause a backfire when the fire comes on and the flame may catch back when shutting off,
owing to the lack of velocity of the gas which is leaking through. A slow leak should never be tolerated. It causes the
car to smell of vaporized fuel, besides causing back-firing.
WHEN FIRE SHUTS OFF
Red-hot coils may radiate enough heat downward to cause the gas to ignite below the burner grate owing to
the radiation overheating the top of the burner.
If the fire is on continuously (caused, for instance, by wet steam), the burner grate may become overheated to
such an extent as to cause the gas to ignite below.
If the vaporizer nozzle is not central to the mixing tube, one part of the burner may receive too much gas and
also too rich a quality thereby causing a hot spot on the burner grate, which would cause ignition below. Aside from
the fact that it causes backfiring, a crooked vaporizer nozzle may very greatly decrease the economy of the car on
fuel. A good way to line up the vaporizer nozzle properly is to watch the jets of gas when first turning on the fuel in
steaming up. The points where the different jets strike the side of the mixing tube may be located exactly and the
nozzle can be set accordingly to a very accurate degree. This subject of having the vaporizer nozzle central is much
more important than the average operator thinks.
