This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol3", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
(Contributed by W. Noakes)
The ordinary form of flat flame burner is either a bats-wing, a slit union, or union jet, as shown in Fig. 106. These are perhaps the most used of all and are made by various firms, it being difficult to say which make, if any, is better than any other, while among quite the best is "Brays" patent. These flat burners are sometimes used in conjunction with an "economiser," which is really a second burner placed over the one which is screwed into the bracket or chandelier, as the case may be, - the principle of the economiser being to provide a greater volume of light than is obtainable by the use of the single burner alone, but at the same expenditure of gas. This result is obtained by using, for example, a No. 4 burner (which passes, of course, a less amount of gas than a No. 7), together with a No. 7 economiser, which gives as large a flame as a No. 7 burner. The action of the burner and economiser is somewhat on the governor principle; the gas has a smaller orifice to pass in the burner than in the economiser, and consequently the pressure is reduced after it leaves the burner outlet, with the result that there is more perfect combustion, while the flame is of the size of that from a No. 7 burner.
Another and probably better means of attaining the object for which the economiser is used, namely, to obtain the best light from the burner without a waste of gas resulting from any excess of pressure, is to use what is called a governor burner. This is really a miniature governor formed in the burner itself beneath the orifice for exit of gas. It should be borne in mind that extra pressure may be and often is caused by other lights being shut off, so confining the pressure to a reduced number of lights or burners, and need not necessarily be constant throughout the complete service. The most efficient burner of this sort to meet such cases is propably the Peebles, as shown in Fig. 107.
The action of this burner is as follows: - The gas enters the inlet of the burner where it is screwed into the fitting, and in the burner above the fitting is a float, which is so fitted that when there is little or no pressure the whole area of the inlet into burner is free for the passage of gas, but when the pressure becomes stronger the float is raised and partly closes or reduces the clear way through the inlet, so that the flow of gas is automatically controlled; for the higher the pressure the less is the clear way through the inlet for passage of gas, and vice versa.
Another excellent burner on this principle is the "Helios," which is fitted with an aluminium float, and is adapted to act under any pressure from 5/10 to 40/10 inch. It is illustrated in Fig. 108.
There are several other forms of flat burners on the market, some of which have distinctive features, but their construction and principles are based on the foregoing examples.
The whole system of gas lighting has been so vastly improved within the last few years by the introduction of the incandescent burner that the great advance made has brought gas lighting within very measurable distance of electric light as a means of domestic and general lighting.
In fact, it is to be questioned whether electric light is any improvement upon a really up-to-date and first-class gas installation; certainly, so far as expense goes, gas is so much the cheaper that with the recent improvements it is a doubtful policy to substitute the electric light for it.
The best known burner is the "Welsbach" of the "C" form, of which an illustration is given in Fig. 109. With about half the consumption of gas required for the flat flame burner it is possible to obtain nearly twice the amount of light by using a good incandescent burner.
The incandescent burner is constructed on somewhat the same principle as the well-known Bunsen burner. The gas is mixed with a certain proportion of air, which is admitted through the circular holes shown in the shield in Fig. 109, and when lighted produces a blue flame which gives out a considerable amount of heat, but until the mantle is placed over the flame the light is of such a nature as to be quite valueless. It is important that the burner should be so constructed that the air and gas will become thoroughly mixed in the correct proportions before ignition, for upon this the efficiency of the burner greatly depends.
The construction of the burner is not in the hands of the gasfitter, and every fitter and very many householders are now thoroughly conversant with its make and different parts, by reason of frequent handling in order to clean and replace broken or damaged mantles, so that it will not be necessary to give any further details.
The mantles are manufactured of ordinary knitted cotton, and, after being made, are washed in a liquid preparation of acid and ammonia, and afterwards saturated in another liquid, of which the chief ingredients are certain forms of very rare earths. They are then dried, and, after being subjected to a flame, are again steeped in further liquids and become ready for use. It is important that the light be applied at the top of the mantle when it is first placed in position, but full directions as to this are given with each mantle sold. The life of a mantle is somewhat variable, and it depends largely on the use to which it is subjected. If it be in a position where draughts may act upon it, or where it is subject to vibration, it will not last long; but with care and if removed from the conditions stated, it is reasonable to expect a good mantle to last for 6oo> to 700 hours.
After the Welsbach, the best known incandescent burner is the Sunlight, and the two are practically the same in construction, as indeed are all the various incandescent burners and mantles on the market. The distinctive difference between the Welsbach and the Sunlight is that the former gives a whiter light than the latter, which is rather of a yellowish tint. The number of incandescent burners and mantles sold now makes it impossible to do anything more than briefly touch on one or two of the best ones.
A most effective form of incandescent lighting now coming prominently into use is the inverted burner, as shown in Fig. no. The distinctive feature about this is that the whole of the constructional part of the fitting and burner is above the light, and consequently nothing retards the illumination. The effect is exceptionally fine, and very closely resembles that of an electric-light fitting. It is excellent for use over a writing or drawing table, where the uninterrupted light and absence of shadows is of much importance.
It is usual to allow, when setting out for the lighting of buildings, 3 superficial feet of floor space per candle-power.
An incandescent burner is equal to about 40 candles, therefore to find the number of lights required for any room, first find the area of the room, and divide same by the space allotted to one candle multiplied by the number of candles in the burner. For example: area of floor, say, 720 square feet, therefore 720/3 = 240 candle-power required ; therefore 6 incandescent burners are needed of 40 candle-power each. To find the number of flat flame burners consuming 5 feet per hour required, divide the floor area by 50. As example : floor area 720 feet/50 = say, 14 burners ; for the illuminating power of such burners is only about 8 candle-power each.
It is frequently found that the pressure in the service is variable, and while it is at one time perfectly even in the whole system, at another time it is excessive, which not only causes a waste of gas, but is apt to create fidgeting noises in burner stoves and fires. Further than this, if the pressure on a burner is very excessive, it not only wastes the gas, but the light obtained from that burner is not so good as if the pressure were properly and evenly controlled. Mention has been made of governor burners, and as far as they can be used they give excellent results ; but in many cases, especially in fires and stoves, the burners are not fitted with governors, and to avoid waste in these cases it becomes necessary to employ a pressure governor. This is a fitting similar in principle to the burner governor, but of course in a much larger scale, as will be seen by reference to Fig. 111.
It is usually adjusted at 8/10 to 10/10 pressure, but can be set to whatever pressure may be required. It should be fixed on the outlet pipe close to the meter, and then governs the pressure perfectly regularly when properly adjusted. It is important that a governor be fixed quite level if it is to work satisfactorily.