Considering one mechanism only, recourse may be had to a diagrammatic representation of the action ([Fig. 5]). Gas entering the inlet passes into the valve chamber. Here an ordinary D-slide-valve closes two of the openings, leaving a third through which the gas may flow into the bellows or inner compartment. The bellows expands, gradually filling the outer compartment, and forcing the gas out under the valve into the outlet pipe, as indicated by the arrows. When the bellows is fully distended the valve shifts into the position shown in [Fig. 6], admitting the inflowing gas to the outer compartment and collapsing the bellows, whose contents are forced into the outlet pipe by the paths traced by the arrows.
Thus, it will be observed, the meter is a volume measurer pure and simple, measuring cubic feet with as much deliberation as is required to deal water out of a cask by means of a pint dipper. Its percentage of error is the same at all pressures and under all loads within its capacity, and it measures cubic feet of gas regardless of whether that gas be expanded or compressed.
And so we are obliged to realize, as another fallacy is exposed, that the meter does not spin around most energetically under the higher pressures, cheerfully and accommodatingly serving its masters by adding a mythical cubic foot or two to the count at each revolution.
It remains, then, to consider the error of the meter. The custom is, in New York at least, not to set a meter that registers fast—that registers a greater volume of gas than actually passes through it. If it is found to be slow, however, and not more than three per cent., it is allowed to go out. As a result, the meter, when first placed, always favors the consumer, sometimes to the extent of recording only ninety-seven feet of gas for each one hundred feet actually passed. Owing to the aging of the mechanism and the drying out of the leathers, there exists a tendency to increase the registry for each cubic foot passed. In this way a slow meter may become a fast meter after a period of active service. From the meager data at my disposal, it would appear that every meter should be called in for a thorough overhauling and readjustment at periodic intervals of from three to five years.
Assuming that there are several million gas meters in Greater New York alone, it is but natural to expect that out of this vast number, in spite of any reasonable care that may have been exercised in their adjustment originally, many will be found subsequently to be defective—some because of mechanical injury, some through sheer old age. Unfortunately, it is not possible as yet to obtain a convincingly large array of figures; but in the Borough of Brooklyn, where there are in service nearly a quarter of a million meters, and where complaints against them have been studiously encouraged by the authorities, one hundred and eighty-seven meters have been carefully tested. Here are the results:
| 21 | correct | |||||
| 114 | fast, average 3 per cent (recording 103 cubic feet for each 100 cubic feet actually passed) | < | 3 | more than 10 per cent. | ||
| 42 | between 3 and 10 per cent. | |||||
| 69 | less than 3 per cent. | |||||
| 114 | ||||||
| 52 | slow, average 2¼ per cent (recording 97¾ cubic feet for each 100 cubic feet actually passed) | < | 0 | more than 10 per cent. | ||
| 13 | between 3 and 10 per cent. | |||||
| 39 | less than 3 per cent. | |||||
| 52 | ||||||
| 187 |
When one remembers that these one hundred and eighty-seven meters are presumably the worst of their kind, having been put in evidence by a naturally suspicious public, it is but fair to assume that the figures overrate rather than underestimate the errors of the average gas meter. Quoting from The Progressive Age, a journal devoted largely to the interests of the gas industry: “The meters made to-day will remain a long while in service before they begin to register incorrectly, and when we consider the dampness, extremes of temperature and hard usage they receive as they are transferred from cellar to attic, from among the dust, cobwebs and litter of a basement closet to the corner shelf of some coal cellar, to be the playground of rats, spiders and cockroaches, to be drenched in summer by sweating or leaky water pipes and wear a venerable beard of icicles in winter—to be, in fact, the worst-used machine about a gas plant—we can not fail but express surprise that it registers at all correctly.”