Handbook of Ship Calculations, Construction and Operation: A Book of ... by Charles Haynes Hughes

Author:Charles Haynes Hughes
Language: eng
Format: epub
Publisher: D. Appleton
Published: 1917-03-25T05:00:00+00:00

Figure 64.—Slide Valve.

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high speed is essential, engines running at 400 or more revolutions per minute are not uncommon. Here the cylinders have a comparatively short stroke and there are at least four. For merchant Vessels revolutions are decreased, the stroke is longer, and the cylinders are larger per horse power developed.

To secure economy in the consumption of steam and hence of coal, the steam, after leaving the low-pressure cylinder, passes into a condenser (see Condensers). In the case of surface condensers they often form part of the engine framing. The back pressure on the low-pressure piston for condensing engines is about 3 lb. per square inch absolute, and for non-condensing 18 lb. absolute.

Paddle-wheel Engines.—These can be divided into two classes, viz., those driving steamers with the wheels on the side and those driving steamers with wheels at the stern.

Side-wheelers either have the engines inclined with the connecting rods working directly on the crank shaft, or vertical with the connecting rod connected to a walking beam from which is a rod that drives the wheel shaft. When the engines are inclined there are two or more cylinders and the steam works expansively. When vertical there is only one cylinder having a stroke of several feet. (See Excursion Steamers and Paddle Wheels.)

Simple beam engines have double poppet valves, generally with fixed Stevens' cut-off and in some cases with adjustable Sickles' dash-pot cut-off. Double trip shafts for raising the main and exhaust valves are on the larger engines, one trip shaft being for hand use and the other for operation by steam, as may be desired. When the boat is maneuvering, or approaching or leaving a pier, the main valve eccentric gear is disconnected.

The main valves of the inclined engines for paddle steamers are usually of the double-beat poppet type, although in some cases there is a balanced slide valve on the high-pressure and double-ported slide valves on the low-pressure cylinders. Stephenson link gear is usually employed although the Walschaert gear has given excellent results. Piston valves have been extensively used.

The main air pumps may be worked by the main engines. The condensers, feed water heaters, filters, and auxiliaries are of the customary types 1 . While jet condensers, in combination with water purifiers, in the past have been installed mostly on the Great Lakes, in recent years surface condensers have been adopted.

Stern-wheel vessels are largely used on the Mississippi and other western rivers in the United States, and on shallow rivers

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