HYDRAULIC PUMPING-ENGIYE.

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of the pump as originally constructed. The apparatus to accom-plish this consists of two opposed small oscillating cylindersconnected to an extension of the plunger-rod of each set ofcylinders, as sliown in the cut at the water end. These cylindersand their connections are filled with water (or other liquid).Compressed air from an aceumulator or storage reservoir isadmitted to the surface of the water (or other liquid) that goesinto these small cylinders, at a pressure suitable to the duty tohe accomplished, for the purpose of maintaining a constant loadat a practically constant pressure on their pistons through themedium of the interposed liquid.

These pistons act in Opposition to the engine up to half thestroke, during which time the steam in the high-pressurecylinder may he at its initial pressure, then the point of cut-offmay he established, and, as the steam-pressure diminishes, theforce that is stored by the compression is given off and isrestored to the source from which it came, securing a practicallyconstant exertion on the piston-rods and water-plungers through-out their whole stroke.

The two small cylinders for the reciprocation of power areplaced directly opposite to, and balance, each other, thus reliev-ing their cross-head from any side strain on the slides.

Tor slide-valve engines of this description the cut-off can hefixed at a suitable fraction of the stroke of the small cylinder,or, in other words, the steam may be taken at a high pressureuntil it only partly fills the small cylinder, then it is expandedto the end of the stroke and admitted to the large cylinder tobe further expanded.

Where the most economic xesults are desired, the low-pressureas well as the high-pressure cylinders on the engine are pro-vided with cut-off valves. These consist of semi-rotating plug-valves placed in the admission ports of the cylinders, and areworked by means of the direct connections shown in the Plate.The point of cut-off can be fixed by experiment for both cylin-ders, and need never be altered while the duty remains thesame.

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