Figure 10-11.-Electrohydraulic steering mechanism. in figure 10-11 will help you to understand the general Getting Planes on Deck principles of their operation. As the hand steering wheel turns in a counterclockwise direction, its motion turns the pinion gear (g). This causes the left-hand rack  (rl) to move  downward  and  the  right-hand  rack  (rz) to move upward. Notice that each rack attaches to a piston  (pl or p2). The downward motion of rack r] moves piston p] downward in its cylinder and pushes the oil out of that cylinder through the line. At the same time, piston  pz moves upward and pulls oil from the right-hand line into the right-hand cylinder. If you follow these two lines, you see that they enter a hydraulic cylinder (S). One line enters above and one below the single piston in that cylinder. This piston and the  attached  plunger  are  pushed  down  toward  the hydraulic pump (h) in the direction of the oil flow shown in the diagram. So far in this operation, hand power has been used to develop enough oil pressure to move the control plunger attached to the hydraulic pump. At this point, an electric motor takes over and drives the pump  (h). Oil is pumped under pressure to the two big steering rams (RI and R?). You can see that the pistons in these rams  connect  directly  to  the  rudder  crosshead  that controls the position of the rudder. With the pump operating  in  the  direction  shown,  the  ship’s  rudder  is thrown to the left, and the bow will swing to port. This operation  shows  how  a  small  force  applied  on  the steering wheel sets in motion a series of operations that result in a force of thousands of pounds. The swift, smooth power required to get airplanes from the hanger deck to the flight deck of a carrier is provided by a hydraulic lift. Figure 10-12 shows how this   lifting   is   done.   An   electric   motor   drives   a variable-speed gear pump. Oil enters the pump from the reservoir  and  is  forced  through  the  lines  to  four hydraulic  rams.  The  pistons  of  the  rams  raise  the elevator platform. The oil under pressure exerts its force on each square inch of surface area of the four pistons. Since the pistons are large, a large total lifting force results. Either reversing the pump or opening valve 1 and closing valve 2 lowers the elevator. The weight of the elevator then forces the oil out of the cylinders and back into the reservoir. Operating  Submarines Another application of hydraulics is the operation of submarines. Inside a submarine, between the outer skin and the pressure hull, are several tanks of various design and purpose. These tanks control the total weight of the ship, allowing it to submerge or surface. They also control  the  trim  or  balance,  fore  and  aft,  of  the submarine. The main ballast tanks have the primary function  of  either  destroying  or  restoring  positive buoyancy to the submarine. Allowing air to escape through hydraulically operated vents at the top of the tanks lets seawater enter through the flood ports at the bottom to replace the air. For the sub to regain positive buoyancy, the tanks are “blown” free of seawater with 10-8