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.
9. The carbide trays should be divided up (by divisions) so that the carbide is wetted in small quantities at a time.
10. A very desirable arrangement is to have the carbide chambers - the generating chambers - in duplicate, arranged to work alternately, so that one may be opened and recharged while the other is on duty. It will be seen that, otherwise, a single chamber must be exhausted before it can be recharged, and the moment of exhaustion may come at night or at some inconvenient time for recharging.
11. The gas as it comes from the generating chambers, and before entering the holder, should be made to pass through water to wash it. This removes certain impurities and finally cools the gas. This water vessel is known as the "washer."
12. On leaving the holder to enter the house services the gas should pass through a chemical purifier. The purifying material commonly used is bleaching powder in a specially prepared form, and is inexpensive. After this final purification, which is quite necessary, the gas is ready to burn.
13. A desirable adjunct in the house service is a "governor," or automatic pressure regulator.
In Fig. 119 are illustrated the details of a generating plant. This is to illustrate the order of the parts, therefore no particular kind of generator is shown. It is quite usual for the generating chamber and the washer to be attached to the holder, so that all are grouped to go into a small hut or house. The detail, which is marked as provided to discharge condense water, is not always put in, some engineers considering a tee, with the outlet plugged, sufficient to discharge any water that may condense in the pipes. With a properly constructed plant the gas entering the house service carries no more water vapour than coal gas does, but it contains sufficient to make a provision for discharge necessary. In the writer's own apparatus of twenty lights the water collected during a year was not sufficient to show its presence in a troublesome way. It was about a quarter of a gill.
The piping of the house service and its branches is carried out as with coal gas, a rise or fall being given wherever desirable to ensure that whatever condense water may collect shall drain to a convenient point for removal. The sizes of the pipes, however, are considerably smaller, as a much less volume of acetylene. is required for a given degree of illumination than coal gas. For the purpose of this detail it may be said that fifteen times as much coal gas is required as acetylene for a light of given candle-power, but it is not practicable to use pipes for the latter of one-fifteenth the size of those used for the former. The following sizes are customarily adopted:-
Number of 1/2-foot Burners, or Equivalent of other Sizes.
Distance from Generating Apparatus (or from the Main, if it is a Branch Pipe).
Size of Pipe.
In carrying out the piping, also in the choice of brackets, it has to be borne in mind, or will be quickly discovered, that acetylene is what is termed a "searching" gas. It will discover and pass through leaky joints and places that would be quite tight to coal gas. Ordinary white and red lead paint may be used for jointing the pipe, but the fitter must not rely too much on the paint. A hot-water or steam fitter makes a sounder job of acetylene piping than the average gas-fitter, but all may do good work if care is used to make soundly screwed joints, with the least possible quantity of white lead. This searching quality of acetylene often makes trouble with the ordinary quality of iron gas pipe, which appears to have too many faulty places in it when carrying acetylene. This is so noticeable - and expensive in labour - that some engineers always use steam tube for this work. It costs but little more in first outlay, and may save much in the end.
For gas-fittings the choice lies between the best quality fittings of the ordinary kinds, or special fittings which have extra long bodies to the joints and cocks. There is no extra wear, nor chemical action, to produce bad results. It is simply that, with acetylene, a fitting must be used that will be sound at its cock and joints and remain sound there when used, otherwise there will be a leak in evidence due to the searching nature of the gas. It is very desirable that copper be avoided in the make of fittings (also in the piping), except for purposes of external ornament. A peculiar chemical action has been found to occur between acetylene and copper, which, although the conclusions arrived at are debatable, is such as to make it desirable that copper be not used where the gas will have contact. Brass, which is an alloy of copper, may be used with freedom and safety. Water-slide chandeliers may not be used, for, as will be learned, the gas pressure with acetylene is too high for water-sealed fittings to be used in the ordinary way.
The burners are of special form, slightly Bunsen in character to rectify the exceeding richness of this gas in carbon. The gas delivery holes are very minute, and, as with most burners giving a flat flame, the gas is delivered as two pin flames which are made to impinge and flatten out. What has been considered the ordinary type of burner resembles Fig. 120. Of all burners it had the greatest use, but it possessed a fault in that the flame could not be turned low without the burner tips "carbonising." This trouble appeared as a small crusted collection of soot, quite spoiling the flame until it had been removed and the burner cleaned. In consequence of this the bracket tap had to be full on or quite closed, if trouble was to be avoided. More recently the firm of Bray & Co. have introduced a burner which is without this fault, and it may be considered that this removed the last difficulty connected with the acetylene industry. Bray's burner is illustrated in Fig. 121. This illustration, it may be noted, shows about twice the actual size of an acetylene flame consuming about 1/2 foot of gas per hour, giving about a 17 candle-power light.
The light afforded by different sizes of burners is as follows :-
Burner consuming per Hour
With Self-Luminous Flame, gives a Light of
• 17.5 "
• 35.0 "
These are sizes ordinarily used, and attention is called to the high illuminating power of the larger burners, which is out of ratio with the gas consumed. It is a fact that the larger the burner the more economical it is, but there has, of course, to be a limit to the size that can be used in residence work. The burners most nearly approaching 5/8 and 3/4 foot are best for this purpose, for it is not economical to use one large burner in a room that requires two burners (at different points and of suitable smaller size) to distribute the light satisfactorily.
There is another reason for keeping the burners of an installation of about the same size, this being that burners of varying sizes require different pressures of gas to afford their best results. The pressures best suited to the burners are as follow :-
Burner consuming Cubic Feet per Hour, or nearest to these Figures.
Most suitable Pressure in Inches of Water.
1/3 foot .
1/2 " . .
2 1/2 "
3 1/2 "
It is seldom that a generating apparatus is so constructed that the holder bell presses down on the contained gas so as to give the exact pressure required at the burners. This is the reason for strongly recommending the use of a governor, as already mentioned, and included in the illustration (Fig. 119).
In setting the governor, or to ascertain the pressure at the burners at any time, a gauge is necessary, and this is illustrated in Fig. 122. It can be home-made if desired, as a piece of 1/4-inch glass tube can be bent in any gas flame. The figured spaces measure half an inch each, but they register an inch, as it will be seen that the water sinks as much below the zero figure as it rises above it. As illustrated, the water is 2 3/4 inches above zero in one leg and 2 3/4 inches below in the other, and this indicates a pressure of 5 1/2 inches. In other words, there is a space 5 1/2 inches in height between the two water levels. By the addition of another cock, to blow into, this gauge can be used for testing a newly finished apparatus. Such an apparatus, before the workmen leave it, should be given a test pressure of 12 to 14 inches of water, and it should bear this with very slight variation for half an hour.