THE CONDITIONS OF PERFECT OPERATION
=General Care.=--Gas-engines, as well as most machines in general,
should be kept in perfect condition. Cleanliness, even in the case of
parts of secondary importance, is indispensable. Unpainted and polished
surfaces such as the shaft of the engine, the distributing cam-shafts,
the levers, the connecting-rod and the like, should be kept in a
condition equal to that when they were new. The absence of all traces of
rust or corrosion in these parts affords sufficient evidence of the care
taken of the invisible members such as the piston, the valves, ignition
devices, and the like.
=Lubrication.=--The rubbing surfaces of a gas-engine should be regularly
and perfectly lubricated. The absence of lost motion and backlash in the
bearings, guides, and joints is of particular importance not only
because of its influence on steady and silent running, but also on the
power developed and on the consumption. As we have already seen in the
chapter on lubrication, a special quality of oil should be employed for
the lubrication of the cylinder. The feed of the lubricator supplying
this most vital part of the engine is so regulated that it meets the
actual requirements with the utmost nicety possible. In a subsequent
chapter, in which faulty operation will be discussed, it will be shown
how too much and too little oil may cause serious trouble.
=Tightness of the Cylinder.=--The amount of power developed depends
principally on the degree of compression to which the explosive mixture
is subjected. The economical operation of the engine depends in general
upon perfect compression. It is, therefore, necessary to keep those
parts in good order upon which the tightness of the cylinder depends.
These parts are the piston, the valves, and their joints, and the
ignition devices whether they be of the hot-tube or electrical variety.
In order to prevent leakage at the piston, the rings should be protected
from all wear. It is of the utmost importance that the surfaces both of
the piston and of the cylinder, be highly polished so that binding
cannot occur. In cleansing the cylinder, emery paper or abrasive powder
should not be employed; for the slightest particle of abrasive between
the surfaces in contact will surely cause leakage. The oil and dirt,
which is turned black by friction and which may adhere to the piston
rings, should be washed away with petroleum. Similarly the other parts
of the cylinder should be cleaned to which burnt oil tends to adhere.
=Valve-Regrinding.=--The valves should be regularly ground. Even in
special cases where they may show no trace of rapid wear they should be
removed at least every month. In order to avoid any accident, care
should be taken in adjusting the valves after the cap has been unbolted
not to introduce a candle or a lighted match either in the
valve-chambers or in the cylinder, without first closing the gas-cock.
Furthermore, a few turns should be given to the engine, in order to
drive out any explosive mixture that may still remain in the cylinder or
the connected passages. The exhaust-valve, by reason of the high
temperature to which the disk and the seat are subjected, should receive
special attention. The valve should be ground on its seat every two or
three months at least, depending upon the load of the engine.
=Bearings and Crosshead.=--The bushings of the engine shaft should
always be held tightly in place. The looseness to which they are liable,
particularly in gas-engines on account of the sharp explosions, tends to
unscrew the nuts and to hasten the wear of the brass, which is the
result of frequent tightening. The slightest play in the bearings of the
engine-shaft as well as in the bearings of connecting-rods increases the
sound that engines naturally produce.
=Governor.=--The governor should receive careful attention so far as its
cleanliness is concerned; for if its operation is not easy it is apt to
become "lazy" and to lose its sensitiveness. If the governor be of the
ball type, or of the conical pendulum type operated by centrifugal
force, it is well to lubricate each joint without excess of oil. In
order to prevent the accumulation and the solidification of oil, the
governor should be lubricated from time to time with petroleum. If the
governor is actuated by inertia, which is the case in most engines of
the hit-and-miss variety, it needs less care; still, it is advisable to
keep the contact at which the thrust takes place well oiled.
The operation of any of these governors is usually controlled by the
tension of a spring, or by a counterweight. In order to increase the
speed of the engine, or in other words, to increase the number of
admissions of gas in a given time, all that is usually necessary is to
tighten up the spring, or to change the position of the counterweight.
It should be possible to effect this adjustment while the engine is
running in such a manner that the speed can be easily changed.
=Joints.=--In most well-built engines the caps of the valve-chests and
other removable parts are secured "metal on metal" without interposing
special joints. In other words, the surfaces are themselves sufficiently
cohesive to insure perfect tightness. In engines which are not of this
class, asbestos joints are very frequently employed, particularly at the
exhaust-valve cap and the suction-valve.
In some engines, where for any reason it is necessary frequently to
detach the caps, certain precautions should be taken to protect the
joints so that they may not be exposed to deterioration whenever they
are removed. For this purpose, they are first immersed in water in order
to be softened, then dried and washed with olive or linseed oil on the
side upon which they rest in the engine. On the cap side they are dusted
with talcum or with graphite. Treated in this manner, the joint will
adhere on one side and will be easily released on the other.
Joints that are liable to come in contact with the gases in the
explosion-chamber should be free from all projections toward the
interior of the cylinder; for during compression these uncooled
projections may become incandescent and may thus cause premature
ignition. As a general rule when the cap is placed in position the joint
should be retightened after a certain time, when the surfaces have
become sufficiently heated. In order to tighten the joints the bolts and
nuts should not be oiled; otherwise the removal of the cap becomes
difficult.
=Water Circulation.=--In a previous chapter, the importance of the water
circulation and the necessity of keeping the cylinder-jacket hot, have
been sufficiently dwelt upon. As the cylinder tends to become hotter
with an increase in the load, because of the greater frequency of
explosions, it is advisable to regulate the flow of the water in order
to prevent its becoming more than sufficient in quantity when the engine
is lightly loaded; for under these conditions the cylinder will be cold
and the explosive mixture will be badly utilized. A suitable temperature
of 140 to 158 degrees F. is easily maintained by adjusting the
circulation of the water. This can be accomplished by providing the
water-inlet pipe leading to the cylinder with a cock which can be opened
more or less, as may be necessary. The temperature of 140 to 158 degrees
F., which has been mentioned, may, at first blush, seem rather high
because it would be impossible to keep the hand on the outlet-pipe. The
cylinder, however, will not become overheated so long as it is possible
to hold the hand beneath the jacket near the water-inlet. This relates
only to engines having a compression of 50 to 100 lbs. per square inch.
For engines of higher compression, a lower running temperature will be
safer. On this matter the instructions of the engine maker should be
carried out.
=Adjustment.=--Gas-engines, at least those which are built by
trustworthy firms, are always put to the brake test before they are sent
from the shops, and are adjusted to meet the requirements of maximum
efficiency. But since the nature and quality of gas necessarily vary
with each city, it is evident that an engine adjusted to develop a
certain horse-power with a gas of a certain richness, may not fulfil all
expectations if it is fed with a gas less rich, less pure, hotter, and
the like. The altitude also has some influence on the efficiency of the
engine. As it increases, the density of the mixture diminishes; that is
to say, for the same volume the engine is using a smaller amount. From
this it follows that a gas-engine ought to be adjusted as a general rule
on the spot where it is to be used.
The fulfilment of this condition is particularly important in the case
of explosion-engines, because an advancement or retardation of only
one-half a second in igniting the explosive mixture will cause a
considerable loss in useful work. From this it would follow that
gas-engines should be periodically inspected in order that they may
operate with the highest efficiency and economy. As in the case of
steam-engines, it is advisable to take indicator records which afford
conclusive evidence of the perturbations to which every engine is
subject after having run for some time.
Most gas-engine users either have no indicating instruments at their
disposal or else are not sufficiently versed in their employment and the
interpretation of their records to study perturbations by their means.
For this reason the advice of experts should be sought,--men who
understand the meaning of the diagrams taken and who are able by their
means to effect a considerable saving in gas.