The Locomotive Of Today

The Boiler : Safety Valves. 41 lever is continued and brought down to a convenient height, and when the valves are located on the firebox wrapper plate, it is carried through into the cab for the engineman to reach when he requires to “try” his valves to make sure that they are in working order. The usual method of setting this.form of valve is to raise the pressure of steam in the boiler, which, in addition to the usual steam gauge has, temporarily, a second fitted to it as a check, the valves are then graclually loaded by adding tension to the spring by screwing up the nut under the bridge until they just lift at the required pressure, then the distance between the upper side of the bridge and the shoulder of the eyebolt is accurately measured, and the steam let down to enable the washer mentioned above to be fitted. A casing of thin metal is placed round the entire arrangement on many engines, which prevents any interfer- ence with the adjustment by unauthorised persons. The safety or side connecting strips above referred to are employed as a precaution to prevent the loss of the valves and lever in case of the breakage of the spring. They have holes for the reception of pins for connection at the bottom to the eyebolt and at the top to the lever, which has a. slotted hole in the central projection, so that they do not interfere in any way with the action of the spring, but ensure the lever standing in an exactly vertical plane, and so prevent any unfair pressure on the valves. This pattern of valve is shown in longitudinal and transverse section at A, Fig. 8, the particular form illus- trated is for an engine with girder stays, and is placed upon a manhole seating. When, however, direct stays are employed, no manhole is provided on the wrapper plate, and the safety valve casting instead of rising from a circular plate, has two pillars branching from a common base fitted to the curve of the boiler, and attached to it by studs. The Ramsbottom valve has the advantag’e of being simple and effeetive, and is, further, difficult to tamper with. Another form of safety valve is the Salter spring-balance, this, however, is not now so common as the last mentioned, but in the earlier clays all locomotives had one or more fitted to them. When used it is usually placed on the dorne, of which the casting containing the valve seatings is made to form the top. The valves are two in number, placed side by side, and similar in shape to those last described; they are often made with a centre pin instead of wings on the Continent. The valves are held down by levers, pivotted, or working under knife edges passing through projecting lugs on the castings and loaded by springs enclosed in cases, a pointed distance piece being placed between the valve and the lever.