Steam locomotive parts
All steam locomotives are fitted with a variety of appliances. Some of these relate directly to the operation of the steam engine; while others are for signaling, train control, or other purposes.
In the United States the Federal Railroad Administration mandated the use of certain appliances over the years in response to safety concerns.
The most typical appliances are as follows water must be forced into the boiler, to replace that which is exhausted after delivering a working stroke to the pistons. Early engines used pumps driven by the motion of the pistons.
Later steam injectors replaced the pump, while some engines use turbo pumps. Standard practice evolved to use two independent systems for feeding water to the boiler. Vertical glass tubes, known as water gauges or water glasses, show the level of water in the boiler.
Steam locomotives in the beginning were fitted with a valve controlled by a weight suspended from the end of a lever, the steam outlet being stopped by a cone-shaped valve.
As there was nothing to prevent the weighted lever from bouncing when the locomotive ran over irregularities in the track, thus wasting steam, the weight was replaced by a more stable spring loaded column, often supplied by Salter, a well-known spring scale manufacturer.
The danger of all these devices was that the driving crew could be tempted to add weight to the arm to increase pressure. Most boilers were from early times fitted with a tamper-proof "lockup" direct-loaded ball valve protected by a cowl.
In the late 1850s, John Ramsbottom introduced a safety valve that became popular in Britain during the latter part of the 19th Century. Not only was this valve tamper-proof, but tampering by the driver could only have the effect of easing pressure.
George Richardson's safety valve was an American invention introduced in 1875 and was designed as to release the steam only at the moment when the pressure attained the maximum permitted.
This type of valve is in almost universal use at present. The earliest locomotives did not show the pressure of steam in the boiler, but it was possible to estimate this by the position of the safety valve arm which often extended onto the firebox back plate; gradations marked on the spring column gave a rough indication of the actual pressure.
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