The Locomotive Of Today

44 1 he Boiler : Pressure Gauges. <_> connection for a pipe to lead the dischargeel steam to the feed water tank tor heating purposes. lo mdicate the pressure carried in the boiler a steam gauge is iitted. Æcommonform is the Bourdon traume, the action of which depends upon the faet that a flattened tube, it subjected to internal pressure, will endeavour to assume a circular section, and, m lts attempt to do so, will straighten itself; thus in the sketch at G, Fig. 8, it will be seen that a pointer indicates the pressure per sq. in. carried in the boiler, on a dial, and the case contains a flattened tube, connected at t ie one end to a casting, which has a union for a pipe from the boiler upon it, and closed at the other with a hin^e or attachmg a connecting rod which actuates a lever on the spindle carrymg the pointer; as the pressure within the pipe tends to straighten it, the closed end with the con- necting rod will move outwards, turning the pointer round on tne cnal. Instead of having a connecting rod direct, the movement can be made by means of a pinion and quadrant, the former bemg on the pointer spindle, and the latter pivotted and connected to the end of the flattened tube. There are numerous variations of this pattern of gauge, but the principle T° m the™ 1S Practically the same, and our illustration the.simplest. It is absolutely necessary with this gauge that the pipe connecting it to the boiler should be formed into a syph°n, so that condensed water may always be in the tube; Ti?1 WaS allowed access to it it would materiallv attect the tube by expansion, etc., and further cause it to soften. 1 ie usual way to form this syphon is, as shown, by carrving- e pipe round the gauge and then make connection, but sometimes a coil is made in the pipe below the gauge. Another form of pressure gauge is shown at H. Here the artiöH depends upon the elasticity of a thin corrugated metal plate or diaphragm, supported round its edge, and subjected fl«?-KeiSS^e °? °ne S,lde’ the extent of the movement of this flexible diaphragm depeneling upon the pressure applied. A vertical rack rises up from the diaphragm, having a ball and socket at its base, and Control led by guides, engages into the teeth ofa. small pinion on the same spindle with a quadrant, hicli m its turn engages a pinion on the pointer spindle, the c laphragm as it rises lifts the rack and the pointer is moved round the dial. Ihe diaphragm has a series of concentric coiTiigations in order to inerease both its sensibility and life. his torm of gauge cloes not require the syphon pipe as the ast does, but may be coupled direct to steam if desired. The i ustration is of an ordinary Schaeffer gauge, modifications of i may be met with, but all embody the same principle of ac,tion.