This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
While the manufacture of gas for cities and towns is a matter beyond the scope of gas fitting, it may not be out of place to take up briefly the operation of one of the forms of gas machines which are used for supplying private residences or manufacturing plants.
The general arrangement of the apparatus is shown in Fig. 70, which consists of a generator, containing evaporating pans or chambers, and an automatic air pump, together with the necessary piping for air and gas. The gas made by these machines is commonly known as carbureted air gas, being common air impregnated with the vapors of gasoline. It burns with a rich bright flame similar to coal gas, and is conducted through pipes and fixtures in the same manner.
Referring to Fig. 70, the automatic air pump is seen in the cellar of the house, and connected to it and running underground are the air and gas pipes connecting it with the generator, which may be a hundred feet or more away if desired. When the machine is in operation, the pump forces a current of air through the generator, where it becomes carbureted, thus forming an illuminating gas that is returned through the gas pipe to the house, where it is distributed to the fixtures in the usual way. The operation is automatic, gas being generated only as fast and in such quantities as required for immediate consumption. The process is continuous while the burners are in use, but stops as soon as the lights are extinguished. Power for running the air compressor is obtained by the weight shown at the right, which must be wound up at intervals, depending upon the amount of gas consumed. An air compressor to be run by water power is shown in Fig. 71. The action of this machine is entirely automatic, the supply of water being controlled by the rising and falling of the holder A, which, being attached by a lever to the valve B, regulates the amount of water supplied to the wheel in exact proportion to the number of burners lighted. If all the burners are shut off, the pressure accumulating in the holder A raises it and shuts the water off. If a burner is lighted, the holder falls slightly, allowing just enough water to fall upon the wheel to furnish the amount of gas required. A pump or compressor of this kind requires about two gallons of water per hour for each burner. The advantages of a water compressor over one operated by a weight are that it requires no attention, never runs down and is ready for immediate use at all times.
The generator is made up of a number of evaporating pans or chambers placed in a cylinder one above another. These chambers are divided by supporting frames into winding passages, which give an extended surface tor evaporation. Fig. 72 shows the generator when set with a brick pit and manhole at one side. It is supplied with mica gages for showing the amount of gasoline in each pan, and with tubes and valves for distributing it to the different pans as required. In small plants the generator is usually buried without the pit being provided, but for larger plants the setting shown in Fig. 72 is recommended. Carbureted air gas of standard quality contains 15 per cent of vapor to 85 per cent of air. A regulator or mixer for supplying gas having these proportions is shown in section in Fig. 73. It consists of a cast-iron case in which is suspended a sheet-metal can, B, filled with air and closely sealed. The balance beam E, to which this is hung, is supported by the pin H, on agate bearings. Since the weight of the can B is exactly balanced by the ball on the beam E, movement of B can only be caused by a difference in the weight or density of the gas inside the chamber A and surrounding the can B. If the gas becomes too dense, B rises and opens the valve C, thus admitting more air; and if it becomes too light, C closes and partially or wholly shuts off the air, as may be required.