OF VARIOUS FORMS, APPLICATIONS, AND APPLIANCES OF THE STEAM ENGINE.
In the English edition of this work, the first part of this chapter is devoted to examples of Portable and fixed Agricultural engines, of different makers and styles of workmanship, but not in sufficient detail, nor illustrated on large enough scale to be of practical value as models, forming rather in fact an illustrated catalogue of the manufacturer, than a study for the mechanic. On this account, they have been entirely omitted, and their place supplied by a few illustrations from American workmanship, not only of Steam Engines, of various forms and applications, but also of various machines, or appliances, connected with the working of engines, as for the determination, or regulation of pressure, of the boilers; for the supply or feed of the boilers, the regulation of the speed of the engine, and the like.
The Gauges used in this country to show the pressures of steam in boilers are of various constructions, but perhaps the most common is the Bourdon, or, as it is known here, the Ashcroft gauge, from the party introducing it, and holding the patent. Fig. 59 represents its interior construction. It consists of a thin metallic tube, a, bent into nearly a complete circle closed at one end, the steam being introduced at the other, at b. The effect of the pressure of the steam on the interior of the tube is to expand the circle, more or less according to the pressure, the elasticity of the metal returning the circle to its original position, when the pressure is removed. The free or closed end of the tube is connected by a link c with a lever d, at the opposite end of which is segmental gear, in gear with a pinion, on which is a hand, which marks the pressure on a dial. The dial and hand are not shown on the cut, but are on the exterior case removed to show the construction.