STATIONARY ENGINES.

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on the varying drain upon the pipes for the ordinary consumptionproved a serious disadvantage; but this drawback was not experi-enced at Grimsby , where the tank upon the tower furnished anuninterrupted supply. In the absence of a natural head of water,with pipes laid for conveying it to a lower Situation, the erection ofwater towers was a serious obstacle in extending the principle ofthe hydraulic crane, and engineering ingenuity resorted to anotherform of head, which possesses the advantages of being applicableat a moderate cost in nearly all situations, and of lessening thesize of the pipes and cylinders by affording a pressure of greatlyincreased intensity. The apparatus by which this is effected hasbeen named the “ accumulator,” because of its accumulating thepower exerted by the engine in charging it. The accumulator isin fact a reservoir giving pressure by load instead of by elevation,and its use is to equalize the duty of the engine in cases where thequantity of power to be supplied is subject to great and suddenfluctuations. In the application of water-pressure machinery, wherean artificial head of water has to be obtained, the real source ofpower is the steam engine employed in pumping the water into theaccumulator, and the w r ater acts simply as a convenient means ofstoring up the power of the engine, and applying it wheneverwanted at the distant points where the work has to be done. Wemay take as an example of this the Victoria Docks in London ,where the area over which the power is extended is so great as torequire 4 miles’ length of mains to convey the water to the severalcranes, hoists, and to the lock-gates.

In Hastie’s variable water-power engine the quantity of water isregulated to the work done automatically. There are two or moreoscillating cylinders rocking on trunnions at their lower ends, thepistons being solid plungers, and centered on a crank pin which isfree to move in a slide, so that the throw becomes variable accordingto the demand on the engine.

THE ACCUMULATOR.

The accumulator consists of a large cast-iron cylinder A (Fig . 20i) ;fitted with a plunger B, from which a loaded case C is suspended togive pressure to the water injected by the engine. The load upon theplunger B is usually such as to produce a pressure in the cylinderequal to a column of water 1500 feet in height, and the cylinder is