Controlling Fluid Pressure

Figure 10-14.-Controlling fluid pressure. hydraulically by remote control, although emergency they may operate manually. in an Hydraulics are used in many other ways aboard submarines. They are used to raise and lower the periscope. The submarines are steered and the bow and stern planes are controlled by hydraulic systems. The windlass and capstan system, used in mooring the submarine, is hydraulically operated. You will find many more applications of hydraulics aboard the submarine. Controlling Fluid Pressure In some hydraulic systems, oil is kept under pressure in a container known as an accumulator. As shown in figure 11-14, the accumulator is a large cylinder; oil is pumped into it from the top. A free piston divides the cylinder into two parts. Compressed air is forced into the cylinder below the piston at a pressure of 600 psi. Oil is then forced into it on top of the piston. As the pressure above it increases, the piston is forced down, squeezing the air into a smaller space. Air is elastic; you can compress it under pressure, and it will expand as soon as the pressure is reduced. When oil pressure is reduced, large quantities of oil under working pressure are instantly available to operate hydraulic rams or motors any place on the submarine. SUMMARY The Navy uses many devices whose operation depends on the hydrostatic principle. You should remember three points about the operation of these devices: Pressure in a liquid is exerted equally in all directions. Hydrostatic pressure refers to pressure at any depth in a liquid that is not flowing. Pressure depends upon both depth and density. The formula for finding pressure is P= H x D The working principle of all hydraulic mechanisms is simple enough. Whenever you find an application that seems hard to understand, keep these points in mind: Hydraulics is the term applied to the behavior of enclosed liquids. Machines that operate liquids under pressure are called hydraulic machines. Liquids are incompressible. They cannot be squeezed into spaces smaller than they originally occupied. A force applied on any area of a confined liquid transmits equally to every part of that liquid. In hydraulic cylinders, the relation between the force exerted by the large piston to the force applied on the smaller piston is the same as the relationship between the area of the larger piston and the area of the smaller piston. Some of the advantages of hydraulic machines are: We use tubing to transmit forces, and tubing can readily transmit forces around corners. Tubing requires little space. Few moving parts are required. 10-10