Popular Science Monthly/Volume 57/June 1900/Gas and Gas Meters
|GAS AND GAS METERS.
By HERBERT S. WYNKOOP, M. E.
WHAT is the matter with our illuminating gas? Why is its quality so poor? Why is it that our bills are creeping up, in spite of the fact that the rate per thousand cubic feet is going down? These are questions that periodically recur to the mind of every householder.
Just why the public has not been educated into a correct understanding of the gas situation is hard to say, unless it be that an inbred prejudice against believing the word of any corporation has led to an utter repudiation of such explanatory statements as may emanate from time to time from the gas office. And it must be admitted that many of the explanations are misleading, either through the intention of the superior officials or by reason of the ignorance of their subordinates.
Hardly has the chill of shortening days driven us indoors in the early twilight before complaints of poor gas become epidemic. Now, what is 'poor' gas? Is the gas deficient in light-giving constituents, or is it merely burned in such a manner as not to afford a satisfactory illumination?
The charter of Greater New York requires that the illuminating gas supplied throughout the city shall be of at least twenty candle power, or illuminating quality, or richness—that is to say, if we burn this gas in a standard burner at the standard pressure (or at as near this pressure as may be), so that the rate of consumption is five cubic feet an hour, the flame thus produced shall be equivalent to twenty standard sperm candles, each burning at the rate of one hundred and twenty grains of sperm per hour, and all bunched—if such a thing were possible. There can be hardly any doubt but that all the gas sent out from modern gas works fulfills the above requirement. Indeed, my own tents give results ranging from twenty-two to twenty-eight candles, with an average of about twenty-four. Manifestly, the gas sent out is not 'poor.'
Nevertheless, the fact that the gas as manufactured is of the required candle power is no indication that the product as delivered to the consumer will give a similarly satisfactory test. Distribution of gas is attended with many perplexities, not the least of which is condensation. The illuminating hydrocarbons, or light-giving constituents held in suspension in the gas. are not so firmly fixed therein as to be unaffected by the size of the pipe, the character of the internal pipe surface, and barometric and thermometric variations. The transmission of gas causes, therefore, a loss of candle power ranging from a small fraction to several candles, although it is possible to conceive of conditions so extraordinarily favorable that the illuminating quality of the gas might be actually improved by distribution.
It will be readily understood from this explanation that tests made at the gas works, or even at points arbitrarily selected at a certain distance from these works, are hardly calculated to satisfy the consumer. For this reason I have preferred, in conducting these tests, to sacrifice to some degree the accuracy that obtains in laboratory experiments, in order to test gas samples taken from the main directly in front of the complainants own premises. I argue that the consumer cares little or nothing as to whether the gas as manufactured complies with the law, or whether tests made at a point perhaps a mile away from the works show the required candle power; but that he does want to know what is the quality of the gas passing in at his service pipe. The method of collecting and transporting to a laboratory the gas samples enables one to say with positiveness that the gas at the point of complaint has an illuminating power of at least so many candles, and that it may be even one candle better than the tests indicate. The figures thus obtained range from twenty and a half to twenty-five. So, then, the gas delivered to the consumer is not 'poor.'
Hygienic reasons demand that the impurities in the gas shall not exceed a definite percentage. Whatever effect these impurities may have upon the candle power has been covered by the tests above explained, so that any further consideration of these impurities may be omitted here.
It is always a difficult matter to convince an indignant householder that the quality of the gas supplied to him is satisfactory. He knows perfectly well that he is not getting the desired result, and no explanation, however elaborate, as to candle power will placate him, unless it be supplemented by a further statement detailing the cause of the trouble. When you are trying to draw water in the bathroom while the cook is filling the washtubs in the basement, do you say the water is 'poor'? Why, then, should you characterize the gas as 'poor,' when people nearer to the gas works than you are happen to be drawing heavily upon the common gas main? Imagine, if you please, a long gas main, with consumers tapping in at points throughout its entire length, and with a gas holder forcing the gas in at one end. Since there is a loss of pressure, caused by the transmission, it follows that the pressure will be higher at the gas holder than anywhere else along the line, the difference in pressure depending, roughly, upon the size and length of the pipe and upon the amount of gas flowing. Now, for any one customer the size and length of pipe will remain constant, but the flow of gas along the line will vary from hour to hour, consequently the pressure at his house may be expected to vary from hour to hour.
The unit of measurement of gas pressure is that pressure which will cause a difference of water level of one tenth of an inch in the two legs of a V-shaped tube when one end is connected with the gas main and the other end is left open to the outer air. Ten tenths, or one inch, is the standard, or normal pressure.
Any appliance—even a gas-burner—operates to best advantage
under certain well-defined conditions. Depart from these conditions, and the efficiency of the device is impaired to an extent depending largely upon the nature of the appliance under consideration. For example, burn an incandescent lamp at fifty per cent, above normal voltage and it breaks down; burn a gas jet at two hundred per cent, above normal pressure, and it still operates—how satisfactorily 'deponent sayeth not.' Now, the gas-burner is supposed to operate to best advantage at ten tenths of an inch. At this pressure the flame is neither so wavering as to be affected by every chance draught, nor so rigid as to permit the gas to blow through without being properly consumed. Below the normal the flame decreases; above, the light is increased somewhat, but not by any means in proportion to the increase in the gas flow. Thus we see that the satisfactory employment of gas as an illuminant depends upon the maintenance of a pressure high enough to deliver the required amount of gas, but not so high as to cause wasteful consumption.
Turning back now to the gas main, let us consider the pressures
actually existing. Exhibit 1 is a photograph of a twenty-four-hour record of pressure at a point not far from the works. The radial lines represent time, and there is a line for each quarter of an hour. The circles represent pressure, there being one circle for each tenth of an inch. Starting at E, the point at which the record begins, and following the irregular line clockwise, one may readily determine the fluctuations of pressure and the time of their occurrence. Interpreting the diagram, we find that the pressure was slightly above the normal until 4.30 p. m. (A), when the works began to raise the pressure little by little, in order to compensate for the increased loss due to increased flow through the mains. At 6.15 p. m. (B), the works ceased increasing the pressure. While this increase lasted—from 6.15 p. m. (B) to 10.15 p. m. (C)—our friend near the works suffered under twenty-one tenths pressure, the gas blowing merrily through the tips and the meter conscientiously registering gas wasted as well as gas utilized. From 10.15 p. m. (C) the pressure falls by steps during the ensuing two hours, finally reaching eleven tenths just after
midnight (D), which latter pressure is quite steadily maintained until the following forenoon. The service from bedtime to dinner time should have proved quite satisfactory. One would naturally expect to find this consumer complaining of high bills, however.
Visiting the fellow at the distant end of the line, we find conditions widely at variance from those already considered. Exhibit 2 tells a new story. The recording gauge was placed in service at 4 p. m. (E), and shortly afterward (A), the pressure began to fall. The jets grew dimmer and dimmer, while the Welsbach mantles became petticoats of red, with hems of white at the bottom. No wonder this man complains of 'poor' gas, while some learned friend, dropping in for an evening cigar, explains that there is 'air in the pipes.' The one consolatory reflection is that, at all events, the poor fellow had a good light to undress by (B to C).
Exhibits 3 and 4 come from my own residence. Together they form a 'before-taking' and 'after-taking' advertisement—not of medicine, but of a gas governor. The fact that 1 am located at a considerable
distance—several miles—from the works, and am supplied through a main laid a number of years ago, when-the territory was sparsely settled, enables me to present Exhibit 3. Comment on this record is unnecessary. After securing this diagram I installed a governor and set it at eleven tenths. Exhibit 4 shows what happened. I am now doing for myself, and at my own expense, that which the gas company fails to do for me. This governor, therefore, renders me almost entirely independent of the gas company; and, in order to demonstrate more clearly to what degree this independence extends, the gauge has been allowed to run for forty-eight hours without changing the card, thus super-imposing the record of the second day upon that of the first. Note how closely the readings for the two days agree. The governor is a protection against excess of pressure only; if the street pressure falls below eleven tenths—the point at which my governor is set—automatic regulation ceases, and my gas simply becomes subject to practically the same variations as exist on the main. Happily, the latter condition is infrequently realized in our neighborhood. No argument is needed to prove how successfully a governing device of this nature can cope with the trouble indicated by Exhibit 1, or how utterly inadequate it is to afford relief from the evil depicted in Exhibit 2. Increased pressure is the only remedy for the latter.
The gas company does not recommend the use of these house-to-house governors—presumably because such a recommendation would be in effect an admission that the service as now maintained by the company is not satisfactory. Indeed, the less enlightened officials—and it is these, unfortunately, with whom the consumer has generally to deal—positively and unreasoningly condemn all such regulating devices. In spite of this, there exist to-day several gas-reduction companies, whose sole occupation consists in exploiting various gas-pressure-regulating appliances, which are rented to consumers for a certain percentage of the monthly saving in the gas bills which their use effects.
It would appear to be a self-evident proposition that when one pays for gas delivered at his meter he is entitled to receive that gas under such a pressure as will afford the most satisfactory service. This pressure is found to be one inch. Making due allowance for reasonable fluctuations of a few tenths above the normal, any further departure from the standard may be taken as a sure indication of a disinclination on the part of the company to meet the expense of new pipes and regulating apparatus. The time is not far distant when the public will demand, not cheaper gas nor better gas, but a more satisfactory service. But before condemning the gas company one must look to his house piping. The company's responsibility ends just inside the meter, and from that point the consumer must provide satisfactory appliances, giving the same attention to the gas pipes as he gives to the plumbing. This is seldom done and the company is frequently blamed for the neglect of the householder.
The gas engineer, steering between the Scylla of 'poor' gas and the Charybdis of excessive pressures, finds himself still 'dangerous in the rapids' of financial expenditure. At present he is doing the best he can with the money doled out to him by the management.
It will be observed that up to the present point the gas meter itself has played no part in the discussion. The meter, although greatly maligned, is in reality an eminently satisfactory piece of mechanism. Concerning this apparatus many erroneous notions prevail. One of these is that a householder may burn thousands of feet of gas without cost to himself, provided he keeps the company in blissful ignorance of the employment of gas for heating purposes upon his premises. The demonstration of the falsity of this idea lies within the reach of any one who will take the trouble to read his own meter on those days on which the company's indexer pays his monthly visits.
Figs. 1, 2 and 3 represent different states of the index usually employed on the three, five and ten light meters, the sizes commonly found in our dwellings. The smaller dial, placed centrally above the other, is known as the 'proving dial,' and, being used merely for testing purposes, is not considered in reading the gas consumption. Although the index dials vary in nomenclature as well as in number, it is generally safe to consider that if the name is placed above the
|Fig. 1.—Reads 3,300 Cubic Feet.
|Fig. 2.—Reads 19,800 Cubic Feet. The apparent reading is 29,800. The gearing of the indexing mechanism is not especially delicate, and it frequently happens that the dial of one denomination begins to record before the hand of the next lower denomination has made a complete revolution.
|Fig. 3.—Reads 19,800 Cubic Feet.
dial a complete revolution of the pointer is required to register the amount of gas indicated by the name; whereas if the name is placed below the dial each numbered division of the dial represents the amount corresponding to the name. If doubt still exists as to the value of each division of the lowest or right-hand dial, remember that no meter index is designed to read less than one hundred cubic feet for each division of the circle.
After one has indexed his own meter for a month or two he is in a position to begin checking the bills presented. The 'present state of meter' and the 'previous state of meter' are always specified, and the mere subtraction of the former from the latter gives the consumption. This is not invariably the case, however. After a meter has registered its maximum reading—100,000 in the smaller sizes—it passes over the zero point and begins to build up a new record. This happens at intervals as long as the apparatus is kept in service. Before me lies a bill giving the 'present state' as 1,700 and the 'previous state' as 96,300. Since the meter was continuously employed, it must have registered up to 100,000, so that it registered 3,700 cubic feet on the old score before recording 1,700 cubic feet on the new. Consequently, adding 1,700 to the difference between 'previous state' and the highest possible reading gives 5,400 cubic feet—the amount consumed during
Fig. 4.-Interior of Common Gas Meter.
the month. By reading one's own meter the detection of any error on the part of the indexer or of the clerical force at the gas office becomes possible. Errors of this nature are of rare occurrence, as those who have adopted this plan of checking gas bills will testify. The responsibility for excessive bills is thus taken from the gas employees and thrown entirely upon the gas-registering mechanism itself. Those people, then, who chuckle furtively over the fact that the gas company has not 'caught on' to the surreptitious use of gas ranges are either the fortunate possessors of 'slow' meters or are deluding themselves as to the amount of gas which they actually consume.
Fig. 4 is a photograph of the common dry meter, with the front, back, top and left side removed. It is called a 'dry' meter to distinguish it from those meters, having little vogue in this country, which employ a liquid in place of a valve motion. The apparatus shown consists of a case divided into three compartments by a horizontal partition one fourth of the way down from the top, and by a vertical partition centrally placed and extending upward from the bottom of the casing to the horizontal partition. The upper compartment contains the registering mechanism and a small valve chamber, the latter corresponding to the steam chest of an engine. In each of the lower compartments is a metal disk attached to the central partition by well-oiled flexible leathers, each disk, leather and the
partition forming a bellows. As in a locomotive, the meter really consists of two separate mechanisms, set to operate out of phase and avoid dead centers.
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:
|fast, average 3 per cent (recording 103 cubic feet for each 100 cubic feet actually passed)
|more than 10 per cent
|between 3 and 10 per cent
|less than 3 per cent
|slow, average 21⁄4 per cent (recording 973⁄4 cubic feet for each 100 cubic feet actually passed)
|more than 10 per cent
|between 3 and 10 per cent
|less than 3 per cent
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."