When gas of any kind is purchased from a manufacturing company, the amount used is measured by a gas meter, located at the point where the gas main enters the building. The readings of the meter are taken by the company at stated intervals and the amount registered is charged to the account of the consumer. Gas is sold in cubic feet and is so registered by the meter. The price is quoted by the manufacturers at a definite rate per thousand cubic feet. The difference between the last two readings of the meter furnishes the amount from which the gas bill is reckoned.

The occupants of a building are responsible for all gas registered by the meter and, therefore, should be acquainted with the conditions under which the gas is sold. Gas bills are often the subject of dispute because of failure to understand the period of time covered by the amount claimed; again, the varying length of days due to the season of the year has a pronounced effect on the amount of gas consumed. Lack of care in the economical use of gas is probably the most prolific cause of disputed bills.

The amount due for gas may at any time be checked by the consumer who keeps a record of the meter readings. At any time the correctness of a meter is doubted, arrangement may be made with the gas company to have it tested for accuracy. This is done in the office of the company, by attaching the meter to a measuring device - called a meter prover - in which a definite measured amount of gas is passed through the meter and comparison made with meter registration. If it is found that the meter does not register correctly, the gas company is in duty bound to make good the difference. If, however, the meter is found to be correct, it is customary to charge for the services of proving the meter.

Gas Meters

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.

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.

Fig. 177. - Gas meter.

Fig. 178. - Gas meter showing internal mechanism.

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.