1240
THEORY AND PRACTICE OF ENGINEERING.
Book II.
the main and service pipes,beautiful contrivance; by it
Fil
munication with the gasometer with a similar pipe. The top cover, which is suspended overpulleys by a balance weight, when raised, allows the gas freely to pass, but when let down,the partition plate, sinking in the water which surrounds the ends of the two pipes, at onceprevents any gas from passing from one to the other: the water is maintained at a uniformheight by means of a small reservoir attached to the side, which is regularly supplied by aball-cock.
Pressure Indicatory which measures the pressure inused at most of the large establishments, and is aascertained the excess or deficiency ofsupply: when a number of burnersare suddenly extinguished or lighted, theindicator at the works immediatelymakes it known; this is effected by thesmall, but nicely-adjusted gasometer,connected with the main service; itsrising and falling being the cousequenceof diminished or increased pressurewithin the main, the valves are eitheropened or shut, to allow the gas topass or not from the gasometer. Tothis is attached a regulating rod, whichhas a pencil inserted in it, which inits motion is made to trace a line upon aruled sheet of paper wrapped round asmall cylinder; this is kept in regularrotation on its axis by means of ma-chinery connected with the movement ofa clock ; thus during the night as wellas day every change of pressure is indi-cated.
This invention of Mr. Crosley’s forregistering the actual pressure at themain outlet, and which indicates themost minute variations, with the pre-cise times when they occur, enables acomplete check to be kept against the
Fig. 1950.
INDICATOR.
person employed to superintend and regulate the supply. In the interior of the smallgasometer is a small tube, which communicates with the main; an air-vessel withinthe gasometer occasions it to float when immersed in the water, at which time it is ina state of equilibrium with the external atmosphere; and as the gas in the main increasesits pressure it rises, which rising is measuredoff by a scale, 12 inches in height, beingequal to the pressure of a column of water
inch in height. The paper by the hori-zontal lines shows every tenth of an inchpressure, and by vertical lines the hourswhen it occurs.
Sliding Valves are very simple, and areplaced in an upright position, within astrong iron frame; they are perfectlysmooth, and the plate which slides upand down is sometimes of brass, properlyground, and made to fill up the groove, andrendered completely air-tight: it is movedup and down by a screw, which turns in asocket formed on the upper part of theframe; but where their dimensions are con-siderable, a rack and pinion may be advan-tageously employed.
A Quicksilver Valve is sometimes used,formed by a square iron box, with a per-pendicular division in it, which can bemade to dip into another iron box below it,and in which a quantity of quicksilveris placed: into the sides of the upper box
QUICKSILVER VALVB.
are inserted the two pipes to allow of the passage of the gas, when it is required; it isobvious that when the division of the upper box does not dip in the quicksilver, the