THEEE-CYLINDEK ENGINES AND CAPSTANS.

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The pressure is always on the outer end of the piston, so tliatthe struts C' are in compression, and take up their own wear.This engine is well adapted for transmitting pressure toappliances wliich are worked intermittently, as, owing to thegreat speed at wliich it can be run, it will not ouly save the lossfrom friction (where gearing is employed), but will also reducethe friction in the machine itself, bv enabling the gearing forincreasing speed to be dispensed with.

The production of a simple hydraulic rotary engine led to itsapplication to eapstans, several forms of wliich have beeil intro-duced. One of the most recent and compact is tliat made atElswick, wliich may be termed the Turnover Hydraulic Cap-stan, as shown by Plate 8. A bed-plate is hinged upon twotrunnious, one admitting the pressure, and the other being usedfor tlie outflow of the exhaust water, after it lras passed tliroughthe working valve or valves. To the bed-plate is cast a pillar,tlirough wliich the crauk shaft is guided, and to the other endof wliich the capstan head.is fixed. To the single crank, 011wliich the three rams act, is attached a cross rod communicatingmotion to a rotary valve, from whieh branch pipes convey thewater to and from each cylinder. The trunnious of the bed-plate are carried on bearings attached to a cast-iron casing,which forms a framework for the capstan, and on wliich alsois carried the working valve for regulating the startiug andstopping of the capstan. This working valve is usually amitred valve, to which a counter-weight and lever are attached,in such a nianner that the counter-weight, when free, keeps thevalve closed. To start the engines, the lever is pressed withthe foot, tlius raising the weiglit which keeps the valves closed.When the foot is removed the valve is closed, and the action ofthe capstan is stopped. The capstan is so balanced 011 thetruunions that it can be easily turned over by one man. Theadvautages of this arrangement chiefly consist in the facilitiesthat are afforded for examining and oiling the parts. Thecapstan can be worked in auy position, so that its action can bereadily seen and adjusted. Tue usual power given to working