What is here meant as “direct-acting,” is a steam-driven pump in which there are no revolving parts, such as shafts, cranks and fly-wheels; _pumps in which the power of the steam in the steam cylinder is transferred to the piston or plunger in the pump in a direct line_, and through the use of a continuous rod or connection. (Fig. 82.) _The introduction of the direct-acting steam-pump marked a point of deviation_, and it entered the field almost without a rival, and at a time when economy was overshadowed by its convenience. In the brief description given of these three most prominent classes of pumping engines, no attempt has been made to describe any of the peculiarities of their general construction, beyond what was necessary to describe their action and the principles upon which they operate. [Illustration: FIG. 82.] In pumps of this construction there are no weights in the moving parts other than that required to produce sufficient strength in such part for the work they are expected to perform, and, as there is consequently no opportunity to store up power in one part of the stroke, to be given out at another, it is impossible to cut off the steam in the steam cylinder during any part of its stroke. The uniform and steady action of the direct-acting steam-pump is dependent alone on the use of a steady uniform pressure of steam through the entire stroke of the piston against a steady, uniform resistance of water pressure in the pump; the difference between the power exerted in the steam cylinders over the resistance in the pump governing the rate of speed at which the piston or plunger of the pump will move. The length of the stroke of the steam piston, within the steam cylinders of this class of pumps, is limited and controlled alone by the admission, suppression and release of the steam used in the cylinders. NOTE.—Up to the introduction of the direct-acting steam pump, all the other pumping machinery of the world then in use was the outcome of evolution. It had been developed by slow stages, in which one engineer after another aided by the experience of others and of his own, supplemented by his inventive faculties, added here and there slight improvements to which other engineers, with increased experience, were enabled to add still other improvements, so that each new engine constructed under more favorable circumstances, and with increasing expenditures, was supposed to excel all previously built; until at this time we have, as it is fair to suppose, pumping engines which combine all the wisdom of the past, and which leave little or no room for further improvements in their respective classes.