All About Engines

The Modern Reciprocating Engine i37 by Watt nearly a hundred and fifty years ago. No reciprocating engine is more economical, none is less costly to maintain or less liable to get out of order. The forced lubrication and the exclusion of dust reduce wear to a minimum. Occupying but little space, and requiring but little attention, it is used for any and every purpose for which a steam engine is required, except for locomotives and ship propulsion. Air Pumps and Condensers The reader will recollect that in Newcomen’s engine the steam was used to force the piston up, and that in order to hurry its descent the steam was con- densed by the aid of cold water. At fiist this water was applied to the outside of the cylinder, but it was subsequently found that a jet of water within the cylinder was more effective. The earlier method is termed “ surface ” condensation, and the later one “jet” condensation. Again, in J arnes Watt s originell experiment with a separate condenser (see Fig. 6) he used an air pump for the first time, and condensed the steam by draw- ing it through tubes immersed in cold water. In his later engines he found that the jet condenser was more effective, because the water and steam came into closer contact with one another. But he con- tinued to use an air pump for the following reasons. All natural waters contain air, which passes through the engine with the steam and does not condense like water. If it is not removed it exerts a back pressuie * In this, of course, the steam was condensed in a separate chamber.