THE ACCUMULATOR.

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diameter, fitted with a piston C, and a piston rod D, which formsthe ram of a hydraulic cylinder E, having T Uth the area of thesteam cylinder B. A steam pressure of 50 lbs. per square inch,therefore, gives a water pressure of 750 lbs. per square inch inthe hydraulic cylinder (less the amount of friction). Steam isadmitted to the top of the accumulator cylinder (at F) fromthe ordinary donkey boiler, or the main boilers. The pumping-engines AA are supplied by a branch, 6, from the oppositeside of the cylinder, and deliver the water from their pumpsinto the hydraulic cylinder at H. The bottom of the accumu-lator-cylinder B is open constantly to the exhaust K. Whensteam is turned on to the accumulator, the engines start, at thesame time pumping up the hydraulic ram D, and they continueworking until the steam-piston rises high enough to close thesteam-pipe orifice G. The engines then stop, but when wateris drawn from the accumulator by the action of the hydraulicmachinery, the steam-piston descends, maintaining the pressureof 750 lbs. per square inch upon the water; at the same time,by opening the steam-pipe G, it starts the engines again, bywhich the accumulator is replenished.

An accumulator has been designed by Mr. Tweddell to meetthe Variation of demand for high pressure water, such as ariseswhen only one appliance is at work in a System of hydraulicpipes supplying numerous shop tools. This is shown byPlate 3, from the Proceedings of the Institution of MechanicalEngineers. The ram or spindle A of this accumulator is fixed,and acts as a guide, whilst the cylinder B slides upon it, and isloaded with the weight uecessary for giving the required pres-sure to the water. The water is pumped in at the bottom at C,and fills up the annular space surrounding the spindle. Thewhole weight has to be lifted by the water acting only on theshoulder D, which is made by a brass bush \ inch thick allround the spindle. A compact arrangement is thus gained, andany required cubic capacity is obtainable by lengthening thestroke. The accumulator is supplied by two pumps, each Ifinch diameter and inches stroke, running at about 100 to