GOVERNOR-BURNERS.
[Sidenote: Effects of excessive pressure with Argand and flat-flame
burners.]
Throughout this treatise, much has been said of the relation which the
pressure of gas, at the point of its delivery from the burner, bears
to the illuminating power of the flame yielded--sufficient to show
that the maintenance of a low and equable pressure in the gas supply
is one of the conditions most imperative to be observed for the
attainment of economy in combustion. Ordinarily, however, this
condition does not obtain at the consumers' burners. The exigencies of
distribution require that, in order to maintain a sufficient supply
wherever gas is needed, a much higher pressure should be kept in the
mains than is requisite for developing, at the burner, the best
results from the gas consumed. Moreover, the pressure at any one point
is subject to continual fluctuations from the variations in the
consumption of gas going on in the neighbourhood. For instance, where
a number of burners are in operation in a house, consuming about the
exact quantities of gas for which they have been constructed, when
part of them are shut off the gas supply to the remainder is in excess
of what is required; and, consequently, the burners do not develop the
same proportion of light from the gas consumed as formerly. Where a
large consumption of gas is suddenly discontinued (as in the business
parts of a town, when the shops and warehouses are closed), the
increase of pressure that is experienced at the burners which remain
in operation is very manifest. The effect of this increase in the
pressure of the gas supply is seen in different directions in Argand
and flat-flame burners. In the former, it causes the flame to smoke,
by permitting more gas to pass through the burner than can be properly
consumed; in the latter, by cooling the flame below the temperature
required for effective combustion, it reduces, in proportion to the
extent to which it is higher than the original pressure, the
illuminating power developed per cubic foot of gas consumed.
[Sidenote: The gas regulator.]
Seeing that economy in combustion can only be attained under the
conditions of an equable pressure, it becomes necessary to subdue the
fluctuations above referred to, or at least to prevent their reaching
the burner. To this end the regulator, or governor, is employed. In
this instrument, a bell dipping into, and sealed in liquid--or else a
flexible leather diaphragm--is actuated by the pressure of the
entering gas, and so connected with a valve as to reduce the area of
the opening which permits gas to enter the instrument in proportion to
the pressure of gas at the inlet; by which means an equable pressure
is maintained at the outlet, no matter what the quantity of gas which
is being consumed, or how the pressure may vary in the inlet-pipe. By
the aid of a governor, fixed on the service-pipe at the entrance to a
building, the pressure of gas at the various burners is rendered
fairly uniform; yet, even then, perfect equality of pressure is not
obtained. The slight friction which the gas experiences in flowing
through the pipes causes the burners to be supplied at somewhat lower
pressures, the farther they are removed from the burner. And, again,
owing to its low specific gravity, gas tends to gain in pressure with
an increased elevation; each rise of 10 feet adding about 1-10th of an
inch to its pressure. From this cause a higher pressure is experienced
in the upper than in the lower rooms of a building. This peculiarity
was observed at an early period in the history of gas lighting; as
Clegg mentions that, in cotton-mills, check-taps were employed to
regulate the pressure of gas at each floor.[12] In order, therefore, to
obtain the desired regularity of pressure in the gas supply, governors
must be employed for each storey; or, what is better still, each
burner must have its own separate governor. And this brings us back to
the subject with which we are more closely concerned.
[12] Clegg's "Treatise on Coal Gas," 1st Ed., p. 197.
The governor-burner, as its name implies, consists of a governor, as
described above (but, of course, on a smaller scale) combined with a
gas-burner; the governor being adjusted so as, whatever excess of
pressure there may be in the gas-supply pipes, to permit only the
quantity of gas to pass which the burner is intended to consume.
Obviously, the principle herein contained is capable of receiving
numerous applications. It can be, and is applied with equal success to
Argand and flat-flame burners; while the modifications which obtain in
the manner of constructing the regulating portion of the apparatus are
almost as numerous and as varied as are the burners themselves. As the
main features exhibited by one are common to all, it is unnecessary to
go into the details of their several constructions. It will suffice to
take two or three of the most successful, or the best known, as
representatives of the whole.
[Sidenote: Giroud's Rheometer.]
Among the first in order of time--and still retaining no unworthy
position in order of merit--is the "rheometer," or "flow-measurer," of
M. Giroud. In this instrument a light metal bell is sealed in
glycerine contained in a cylindrical case; the bottom of this latter
containing the inlet-pipe, screwed for connecting to the ordinary
fittings, while from the centre of its cover rises a tube leading to
the burner. The bell is pierced by a small hole for the passage of the
gas, and is surmounted by a cone-shaped projection, which constitutes
the valve of the instrument. As the pressure of the entering gas lifts
the bell, it causes this cone-valve to enter the mouth of the tube
leading to the burner; reducing the area of the opening in proportion
to the pressure of gas acting upon the under side of the bell, and so
permitting only the required quantity of gas to pass to the burner. It
might be thought that the presence of liquid would constitute an
objection to the use of the instrument; but, as glycerine does not
evaporate, when once the instrument is fixed and properly adjusted, it
needs no further attention. With an excessive initial pressure, there
is, however, a liability of the gas to bubble through the sealing
liquid, and so destroy the efficiency of the instrument; but this
might be obviated by increasing the depth of the bell, and so giving
it a greater seal. The instrument is very reliable for the purpose
which it is intended to fulfil; delivering, through a considerable
range of pressure beyond that required to raise the bell, the exact
quantity of gas for which it has been adjusted. It may be added that
the rheometer has an advantage over many instruments of its class, in
that it presents so little obstruction to the downward rays of the
flame.
[Illustration: FIG. 16.--GIROUD'S RHEOMETER.]
[Sidenote: Sugg's Christiania governor-burner.]
Mr. William Sugg, in his regulator or governor, adopts an entirely
different arrangement to the foregoing. The valve is placed at the
inlet of the governor; and not at its outlet, as in the instrument
just described. Instead of a metal bell, a diaphragm of thin and very
flexible leather is employed, which is raised by the pressure of the
entering gas, and, in turn, actuates the valve; closing the entrance
to the governor in proportion to the pressure of gas acting upon it.
The orifice communicating between the under and the upper side of
the leather diaphragm is controlled by a screw, whereby the quantity
of gas delivered to the burner can be regulated according to
requirements; but when once it has been adjusted to give any desired
pressure of gas at the burner, this pressure will be strictly
maintained, no matter with what excess of pressure (within reasonable
limits) the gas may be supplied to the instrument. The improved
"London" Argands produced by Mr. Sugg (the details of the construction
of which have been already described) are too delicately adjusted to
be applied with advantage directly to the ordinary consumer's
gas-fittings, or wherever any variation in the pressure of the gas
supply is likely to be experienced. However, with the addition to them
of the above governor, their use becomes as easy and simple as that of
other burners; and thus the gas consumer is enabled to obtain the
benefit of the most improved apparatus without being called upon to
exercise the constant care and attention which, without the aid of the
governor, would be necessitated. Besides being applied to Argands,
this governor is successfully applied by its inventor to his
flat-flame burners. In conjunction with a simple steatite burner of
the latter class, it has received a very extended application, under
the name of the Christiania governor-burner.
[Sidenote: Sugg's Steatite-float governor-burner.]
Recently, however, a new type of governor, for application to burners,
has been brought out by the same manufacturer, the construction of
which is very different to that of the instrument referred to above;
and as it is somewhat simpler in its details, and withal appears to be
cheaper in construction, it seems destined to supersede the former
instrument. In this new governor, instead of a leather diaphragm,
there is a bell (or float) of steatite, which is free to move, in the
manner of a piston, within an inner cylindrical chamber contained
within the outer case of the instrument. Attached to the centre of the
float, and on its upper surface, is a tube sliding within another tube
of somewhat larger area; the latter forming a continuation of the
inner cylindrical chamber. The smaller tube is open at both ends, and
thus communicates from below to above the float; the outer tube is
closed at the top, but has an orifice in its side. The action of the
instrument is as follows:--The gas, entering below the float, passes
through the inner tube to the upper part of the cylindrical chamber,
and thence, through the orifice in the outer tube, to the burner. As
the pressure of the entering gas exceeds that required to overcome the
weight of the float, the latter is raised; the tube which is attached
to it being propelled farther into the outer tube in which it slides,
and, in so doing, partially closes the orifice in the side of the
latter. In this way, according to the pressure of the gas acting upon
the under side of the float, the area of the opening through which it
must flow to get to the burner is reduced; and so the quantity of gas
which issues from the burner remains the same under all pressures
above that required to actuate the float. The instrument appears to be
as reliable as it is simple, and to contain few parts calculated to
get out of order; but, of course, whether or not it will retain its
good qualities after long-continued use can only be proved by
experience.
[Illustration: FIG. 17.--SUGG'S STEATITE-FLOAT GOVERNOR.]
[Sidenote: Peebles's needle governor-burner.]
[Sidenote: Efficiency of the needle governor-burner.]
Another instrument of this class--the last which I shall notice--is
Peebles's needle governor-burner. For simplicity combined with
remarkable efficiency, it is undoubtedly ahead of all its compeers.
Somewhat similar in principle to Giroud's rheometer, it differs from
that instrument in many of the details of its construction; and while
dispensing with the use of liquid, maintains equal efficiency in
operation. It was described as follows by Dr. W. Wallace, in a lecture
on "Gas Illumination," delivered before the Society of Arts in
January, 1879:[13]--"In a little cylinder stands a so-called needle, on
the point of which rests a flanged cone of exceedingly thin metal. At
one side of the cylinder there is a small tube leading away the gas,
and the orifice of which is influenced in area by the action of the
cone. The instrument, by means of a screw leading into the side tube,
can be made to deliver any desired number of cubic feet, which it does
with surprising accuracy, provided that the pressure of the gas is not
less than 6-10ths of an inch." As to the efficiency of the instrument,
Dr. Wallace proceeded to state:--"In trials that I have made, I have
not found the variations of volume at different pressures to exceed 1
per cent." For situations where this extreme nicety of operation is
not absolutely essential, or where the rate of consumption is to be
invariable, the instrument is constructed in a somewhat modified and
simpler form. The small tube on the side of the instrument is
dispensed with, and the gas permitted to pass through perforations in
the lower part of the cone. With this alteration there is a nearer
approach to the construction of the rheometer; but, as in that
instrument, there is no provision for altering the rate of consumption
to suit different circumstances.
[13] See _Journal of Gas Lighting_, Vol. XXXIII., p. 162.
[Illustration: FIG. 18.--PEEBLES'S NEEDLE GOVERNOR.]