Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/107

Rh GAS of water impairs their measuring power, which may also be affected by the meter being lifted off the level. The freezing of the water also frequently occasions trouble, and the action of the water on the gas passing through it by dissolving out part of the valuable illuminating l1ydrocar- bons on the one hand, and diffusing watery vapour through it on the other, doubly affects its illuminating power. ‘The dry meter is free from the defects just mentioned, but does not pass the gas with such steadiness as the wet meter. The ordinary dry meter consists of an oblong box enclos- ing two measuring cylinders, with leather sides which con- tract and expand as they are being emptied and ﬁlled, on the principle of ordinary bellows. The pressure of the gas entering this meter is suftieient to keep it in operation, and by a system of valves the one cylinder is in process of filling as the other is being emptied through the service pipe. The chambers communicate by means of lever arms with a crank which turns a train of wheels in connexion with the indicator dials on the face of the machine. Consumers’ G'overnor.—In order to consume gas in a perfectly uniform and economical manner, it is essential that the pressure at the burners should be always in- variably the same. That pressure is liable, however, to variation from a number of causes, such as ﬂuctuation in the number of lights in use, either in the house or in the neighbourhood, or the application or withdrawal of pressure at the works’ governor. And as all good burners are ﬁtted with regard to a ﬁxed standard quality and pressure of gas to be consumed, if this is not maintained the conditions of maximum illuminating power are lost. A consumers’ governor secures uniformity of pressure at all the burners supplied by the pipe on which it is placed. The prin- ciple of the governor is identical with that of the station governor already described, increased pressure in both cases causing the oriﬁce through which the gas escapes to be contracted. The mechanical arrangements by which this contraction of oriﬁce is effected are various. In some instances they are in direct contact with the separate burners, while other governors are applied to the supply pipes of a whole establishment. They are separable into pressure governors, which, like the station governors, give a constant or uniform pressure under all variations of con- sumption, and volumetric governors which pass a constant volume or amount of gas under all variations of pressure. Of pressure governors the forms devised by Sugg and Br11ce Peebles are in extensive use, the latter especially being much _applied to street lamps. In Sugg’s consumers’ governor (ﬁg. 17) QUTLET FIG. 17.—Sugg’s Consumers’ Governor. the gas enters at the inlet, and, following the course indicated by the arrows, passes through the regulating plate of the governor into the gas-holder, and thence, by the opening provided for it, it reaelies the outlet. The gas-holder has suspended from a disc in the crown a half-ball valve, which closes or opens the opening in the regulating plate as the gas-holder rises or falls. A weight placed 011 the top of the holder ﬁxes the pressure required to raise it. As a consequence, if the pressure of the gas on the inlet is greater than that required to lift the holder, then the latter rises, carrying the half-ball valve with it, till such time as the opening left between the sides of the valve of the regulating plate is sufficient to allow 97 the passage of the necessary quantity of gas to balance the holder. On the other hand, if the pressure at the inlet falls below that required to lift the holder, the full opening of the regulating plate allows all the gas there is to pass through the governor to the burners. Where a very perfect control is desirable, the parts of the governor are made in duplicate, and a double control is thus established. Vith certain structural differences the action of the Bruce Peebles governor (ﬁg. 18) is the same. The gas enters at 1, Fig. 18.—Consumers’ Governor (Peebles). and passes out at 2 into the pipe leading to the burners. To adjust the governor the brass cap 3 is unscrewed, and the weights 4 taken off or put on until the desired pressure, of say 5-tenths, at the burne1‘s is obtained, when the brass cap is again screwed to its place. The weights now keep the valve 6 open so long as 5-tenths pressure is not ex- ceeded in the main; b11t any variations in the main above that pressure act at once on the diaphragm 5, and partly close or open the valve, thus maintaining under all cir- cumstances a steady outlet pressure. Of volumetric governors the best known is Giroud’s glycerin rheometer, which consists of a closed cylindrical casing containing a. very light metal dome or ball dipping into a circular channel ﬁlled with glycerin. In the upper part of the dome is a small oriﬁce through which the gas passes, and on its top is ﬁxed a conical valve which works in a seat at the top of the casing. As the pressure from the supply side rises or falls, the bell responsively moves up or down, opening or closing by the conical valve the oriﬁce by which the gas passes outward; and so deli- cately is this compcnsation adjusted that the gas passed is the same in amount however different the pressure. Bruce Pecbles has invented a simple and inexpensive form of volumetric governor (ﬁg. 19), in which the use of glycerin is dispensed with. It consists of a conical dome resting on a. needle-pointed stud, the cone having an orifice at C, and there is besides a variable consumption -‘-7 _ channel at the side A B A, wl1icl1 can be F1G- 19~"V°l“m“t“° controlled by the external screw. As soon G0"9m01' (P"9b1e5)- as the stopcock is opened the gas ﬁlls the interior of the cone, and momentarily closes the valve; but, ﬁnding its way by the vertical passage, or through the hole C, in the cone, it reaches the chamber above the cone. The cone is therefore now surrounded by gas at the same pressure, and, having nothing to support it, falls, and lets gas pass to the burner. But this only takes place to a11 extent that allows a differential pressure to be established suffi- cient to support the colic, which is then equilibriated between two pressures ; and the difference between these two pressures remains constant, however much the initial pressure of the gas may vary, unless, of couise, it gets so low as not to be able to raise the cone. Bm~ne7*s.—The question of the arrangements by which the maximum illuminating power may be developed in the consumption of gas, being one which principally affects individual consumers, has not received the attention which their importance merits. As a rule, gas-ﬁtters are ignorant of the principles involved in the economical use of gas, and are often prejudiced by the assertions of certain inventors; and thus it happens that, owing to defective ﬁttings, unregulated pressure, and imperfect burners, an enormous loss of illuminating power is suffered. In their report to the Board of Trade in 1869, the referees under the City of London Gas Act state, of a large number of burners examined by them, that X. — I 3