Figure 10-11.-Electrohydraulic steering mechanism.in figure 10-11 will help you to understand the generalGetting Planes on Deckprinciples of their operation. As the hand steering wheelturns in a counterclockwise direction, its motion turnsthe pinion gear (g). This causes the left-hand rack (rl) tomove downward and the right-hand rack (rz) to moveupward. Notice that each rack attaches to a piston (pl orp2).The downward motion of rack r] moves piston p]downward in its cylinder and pushes the oil out of thatcylinder through the line. At the same time, piston pzmoves upward and pulls oil from the right-hand line intothe right-hand cylinder.If you follow these two lines, you see that they entera hydraulic cylinder (S). One line enters above and onebelow the single piston in that cylinder. This piston andthe attached plunger are pushed down toward thehydraulic pump (h) in the direction of the oil flow shownin the diagram. So far in this operation, hand powerhas been used to develop enough oil pressure to movethe control plunger attached to the hydraulic pump. Atthis point, an electric motor takes over and drives thepump (h).Oil is pumped under pressure to the two big steeringrams (RI and R?). You can see that the pistons in theserams connect directly to the rudder crosshead thatcontrols the position of the rudder. With the pumpoperating in the direction shown, the ship’s rudder isthrown to the left, and the bow will swing to port. Thisoperation shows how a small force applied on thesteering wheel sets in motion a series of operations thatresult in a force of thousands of pounds.The swift, smooth power required to get airplanesfrom the hanger deck to the flight deck of a carrier isprovided by a hydraulic lift. Figure 10-12 shows howthis lifting is done. An electric motor drives avariable-speed gear pump. Oil enters the pump from thereservoir and is forced through the lines to fourhydraulic rams. The pistons of the rams raise theelevator platform. The oil under pressure exerts its forceon each square inch of surface area of the four pistons.Since the pistons are large, a large total lifting forceresults. Either reversing the pump or opening valve 1and closing valve 2 lowers the elevator. The weight ofthe elevator then forces the oil out of the cylinders andback into the reservoir.Operating SubmarinesAnother application of hydraulics is the operationof submarines. Inside a submarine, between the outerskin and the pressure hull, are several tanks of variousdesign and purpose. These tanks control the total weightof the ship, allowing it to submerge or surface. They alsocontrol the trim or balance, fore and aft, of thesubmarine. The main ballast tanks have the primaryfunction of either destroying or restoring positivebuoyancy to the submarine. Allowing air to escapethrough hydraulically operated vents at the top of thetanks lets seawater enter through the flood ports at thebottom to replace the air. For the sub to regain positivebuoyancy, the tanks are “blown” free of seawater with10-8
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