Locomotive Engine Running and Management by Angus Sinclair

Author:Angus Sinclair
Language: eng
Format: epub
Publisher: John Wiley & sons, inc.
Published: 1915-03-25T05:00:00+00:00

Fig. 37

Fig. 38

exhaust-steam in this case will pump only about a half stackful out of the smoke-box with each puff of steam, and the necessary vacuum will be maintained partly by the pumpmg action and partly by friction of the escaping steam on the gases. A higher steam velocity is required to create the needed draft in this case.

Fig. 37 illustrates a defect of exhaust action very common where double nozzles are used. Its effect is similar to that mentioned in the last paragraph; but

in some cases it is much worse, for the exhaust-steam hugs the side of the stack the whole way up, and by that means loses a portion of its draft-creating power. This same effect sometimes comes from a single nozzle being set out of plumb.

Fig. 38 illustrates another pernicious form of bad adjustment. In this case the steam strikes wide at the base of the stack, and delivers some of its volume into the smoke-box, which impairs the efficiency of the pumping action.

Although in these illustrations I have used only the open stack, the defects pointed out apply equally well to engines having low-nozzles, petticoat-pipes, and diamond stacks.

EXHAUST-PIPES AND NOZZLES

The first function of an exhaust-pipe is to convey the used steam from the cylinders. The form that will carry off the steam so that the least possible degree of back-pressure is left to obstruct the piston is the best for locomotives. The best form that can be used will cause considerable back-pressure at high piston-speeds. When the exhaust-pipe is designed to open at the bottom of the smoke-box, it is necessary to use double-nozzles, to prevent the presence of severe backpressure in the cylinders caused by the steam passing through the exhaust-pipes from one cylinder into the other. The two pipes come together below in such a shape that this cannot be prevented.

When double-nozzles are used with a high exhaust-pipe, the greatest possible care should be taken to adjust the nozzles to deliver the steam as nearly cen-

tral in the stack as possible. When an engine having this arrangement is not steaming satisfactorily, it is a good plan to watch how the steam strikes in the stack.

Where a high exhaust-pipe is used, it is best to employ a single nozzle. Careful experiments have proved that a well-designed exhaust-pipe ending in a single nozzle gives the best results in creating draft; but unless the exhaust-pipe is large and properly shaped, the engine is Ukely to suffer from back-pressure in the cylinders.

It might naturally be supposed that the arrangement of exhaust which produced in the highest vacuum would produce the best results in steam-making; but that is not always the case. Very carefully conducted experiments, carried out to find the relative value of different draft appliances, showed decidedly that a lower smoke-box vacuum would keep up steam with a well-arranged single nozzle than with any form of double-nozzle. The tendency of the double-nozzle was to make an uneven vacuum in the smoke-box. That is, there would be a higher vacuum near the place where the exhaust-steam passed than at any other part of the smoke-box.

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