—The gas meter as ordinarily used is shown in Fig. 177. In Fig. 178 the same meter is shown with the top and front exposed.
Fig. 177.—Gas meter.
Fig. 178.—Gas meter showing internal mechanism.
The meter is operated by the pressure of the gas which enters at the inlet pipe on the left-hand side of the meter as you face the index. The gas from this pipe comes into the valve chamber and passes alternately into the diaphragms and their chambers, as the valve ports V are opened and closed by the action of the meter. The movement of the valve in opening the port which admits gas to the diaphragm closes the port to the chamber which has filled. The gas entering the diaphragm expands it like a bellows and forces the gas out of the chamber, through the middle part of the valve into the outlet pipe F. While this action is going on, the gas is entering the case compartment on the opposite side of the meter and also forcing the gas from its diaphragm through the opening F.
While the meter is in operation, one of the diaphragms and one of the case compartments are filling while the others are emptying. The movement of the diaphragm discs is transformed to the recording dial by the connecting levers shown at the top of the figure. The movement of these levers is such as to produce a rotary motion to a tangent which is attached to a shaft that operates the recording dial. The tangent is carried around in a circle by the action of the arms and its movement is registered on the index of each cycle of the diaphragms.
The measurement is accomplished by the displacement of a definite amount of gas with each movement of the discs; first, from the chamber and then from the diaphragms.
HOW TO READ THE INDEX
The index of a gas meter looks quite complicated, but it is really a very simple contrivance. The small circle on the top in Fig. 177 is for testing purposes only and need not be considered. The dial of Fig. 177 is shown in Fig. 177A. The first circle, marked 1 thousand, registers 100 feet for each figure, 1000 feet for the entire circle. If the pointer stood on 9 it would mean 900 cubic feet. The second circle registers 1000 for each figure, or 10,000 for the entire circle. When the pointer of the first circle has been around once, it reaches 0 on that circle, but the hand on the second has moved to figure 1, showing 1000 feet used. The process goes on until the pointer of the second circle has traveled around and stands at zero. The pointer on the third circle, however, has moved to 1, indicating 10,000. This explanation shows the general plan of the index. A few minutes study of it will render the index as easy to read as the face of a clock. Of course, the pointers do not always stand exactly on the figures as they move from figure to figure as the gas is used.