Figure 10-14.-Controlling fluid pressure.hydraulically by remote control, althoughemergency they may operate manually.in anHydraulics are used in many other ways aboardsubmarines. They are used to raise and lower theperiscope. The submarines are steered and the bow andstern planes are controlled by hydraulic systems. Thewindlass and capstan system, used in mooring thesubmarine, is hydraulically operated. You will findmany more applications of hydraulics aboard thesubmarine.Controlling Fluid PressureIn some hydraulic systems, oil is kept underpressure in a container known as an accumulator. Asshown in figure 11-14, the accumulator is a largecylinder; oil is pumped into it from the top. A free pistondivides the cylinder into two parts. Compressed air isforced into the cylinder below the piston at a pressureof 600 psi. Oil is then forced into it on top of the piston.As the pressure above it increases, the piston is forceddown, squeezing the air into a smaller space. Air iselastic; you can compress it under pressure, and it willexpand as soon as the pressure is reduced. When oilpressure is reduced, large quantities of oil underworking pressure are instantly available to operatehydraulic rams or motors any place on the submarine.SUMMARYThe Navy uses many devices whose operationdepends on the hydrostatic principle. You shouldremember three points about the operation of thesedevices:Pressure in a liquid is exerted equally in alldirections.Hydrostatic pressure refers to pressure at any depthin a liquid that is not flowing.Pressure depends upon both depth and density.The formula for finding pressure isP= H x DThe working principle of all hydraulic mechanismsis simple enough. Whenever you find an application thatseems hard to understand, keep these points in mind:Hydraulicsis the term applied to the behavior ofenclosed liquids. Machines that operate liquidsunder pressure are called hydraulic machines.Liquids are incompressible. They cannot besqueezed into spaces smaller than theyoriginally occupied.A force applied on any area of a confined liquidtransmits equally to every part of that liquid.In hydraulic cylinders, the relation between theforce exerted by the large piston to the forceapplied on the smaller piston is the same as therelationship between the area of the largerpiston and the area of the smaller piston.Some of the advantages of hydraulic machines are:We use tubing to transmit forces, and tubing canreadily transmit forces around corners.Tubing requires little space.Few moving parts are required.10-10
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