The Locomotive Of Today

The Boiler: Safety Valves. 39 The double valves are generally 3-in. in diameter, whilst the third, if provided, is a smaller one of 2-in. diameter, screwed down to blow off at 3-lb. per square inch higher pressure. The best position upon the boiler to place the valves would appear to be upon the wrapper plate, it being there farthest from the dorne where steam is being drawn off through the regulator to the cylinders, as when an engine primes it generally causes an unusual generation of steam which escapes at the safety valves; this in its passage is liable to accumulate and lift the surface water and foam, thus the further they are placed from the dorne the better, as they will then tend to diminish the evil of priming at that end rather than increase it as they probably woulcl do if placed there. It is very necessary that the pressure should not exceed the desired limit and. to prevent tampering with the safety valves, ferrules or washers are iitted under the holding down arrangements, so that whilst it may be quite easy to relieve them and allow steam to blow off before the fixed pressure is reached, it is almost impossible to exceed it without employing means which are easily detected. The most common form of safety valve to be met with on British locomotives is that introduced by Ramsbottom. in 1855. It was originally, and is still in some cases, constructed of brass, but now it more usually consists of an iron casting forming two hollow pillars, which stand vertically upon a circular plate, these are in communication with the boiler at the base, whilst the valves close them at the upper ends; the valves are held down by means of a spring pulling on a lever which crosses the pillars and rests on each, the lever has a lug upon it projecting' downwards between the pillars, to which the upper end of the spring is attached. Near the base of the pillars a bridge piece is cast between them, an eyebolt passes through a square hole in this and is secured by a nut under- neath; the eyebolt has two holes, the lower one being for the reception of the lower end of the spring, and the upper one to connect safety strips mentioned later. Between the shoulders of this eyebolt and the bridge is insertecl a washer, made the exact thickness required after adjustment to form a lock. The valves are made of gun-metal and are of the wing type, deeply coned at the top for the reception of the bearing points of the holding down lever. When the casting is of iron the valves take their seats upon bushes of gun-metal inserted into the upper ends of the pillars. The lever, or, as it is often called, the “cowtail,” is made of a piece of flat wrought iron, with a hinged joint to take the bearing on one valve, whilst a plain projection upon the lever holds down the other, one end of the