Pounds. For convenience of expression it will probably simplify matters to refer to all disagreeable and annoying jerks and sounds familiar to the locomotive engineer and fireman as "pounds". By different individuals these characteristic sounds may be referred to as clicks, knocks, jerks, thumps, pounds, bumps, thrashes, etc. In actual practice they are sometimes very difficult to locate. If a serious pound is neglected or disregarded, it may be the cause of ultimately disabling the locomotive. Because of this fact an effort should be made to locate all troublesome pounds and report them promptly, for by so doing the engineer will relieve himself of further responsibility. An experienced locomotive engineer naturally becomes familiar with all the various sounds produced by a locomotive when in operation and can very often locate a pound which develops suddenly by the particular sound. Perhaps one of the most difficult pounds to locate is one caused by a loose piston. Improvements made in more recent locomotives reduce the chances for the development of such pounds very materially. When they do develop, they often will deceive old experienced operators. They usually develop rather suddenly and sound as if there was much lost motion somewhere, when as a matter of fact the exact amount of lost motion may be exceedingly small. Such a pound will probably be taken for a loose driving box or crosshead.Locating Pound. Having detected an unusual knock or pound, it should be located and corrected at the first opportunity. When it has been determined from which side of the locomotive the pound issues, it can be definitely located in the following manner: Block the driving wheels as securely as possible with the crank-pin on the side in question at the top quarter and have the fireman open the throttle slightly, to give the cylinders a little steam, and then reverse the engine a few times while an examination is made of the various points where a pound is liable to develop. The crank pin is placed on the upper quarter because in that position the parts are freer to move than with it at any other point. If it were placed at either dead center, steam could be admitted at but one dead center, no matter where the reverse lever was placed.
Causes of Pounds. Pounds may result from improper lubrication of various parts, such as the valve and piston, main axle, main crank-pin, and crosshead, or lost motion in the reciprocating parts. Pounds will also result from loose wedges, loose knuckles, wedges down or stuck, broken engine frame, cylinders loose on frame, loose pedestal braces, imperfect fitting of shoes and wedges, loose oil cellars, and shoulders worn on either the shoes or wedges or on both. At times when the boiler is priming badly, water in sufficient quantities may enter the cylinder and cause pounds and endanger the safety of the parts. Improper valve setting or adjustment may be the cause of pounds or noises of different character. In this case the usual cause would most probably be too late admission or too great compression. Other conditions remaining the same, admission should increase as the speed increases. In order to determine whether or not the valve adjustment is responsible for unusual noises or knocks, it will usually be necessary to take indicator diagrams from which a study can be made of the steam distribution.
The valve gear or reversing mechanism is frequently the cause of numerous rattling noises. The valve gears commonly employed embody a number of pins, links, movable parts, etc., which become worn and result in lost motion. The wear on any one part may not be very noticeable, but in the aggregate the lost motion may be quite large. The locomotive engineer can usually locate the badly worn parts when the locomotive is stationary by having the fireman throw the reverse lever first forward then backward, repeating the operation as often as necessary, while inspecting the various parts. This method would probably not disclose lost motion which might exist in the eccentrics.
The side rods cannot be operated successfully if adjusted too snugly. For this reason they are made to work with freedom and frequently produce a rattling sound. This rattling should not be confused with a pound.
Table of Contents; Page 169; Page 172; Index
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