square inches. With a resistant force on piston 2, a downward force of 20 pounds acting on piston 1 creates 10 psi (20÷2) in the fluid. Although this force is much smaller  than  the  applied  forces  in  figure  10-1,  the pressure is the same because the force is concentrated on a relatively small area. This pressure of 10 psi acts on all parts of the fluid container, including the bottom of the output piston 2; therefore, the upward force on the output piston 2 is 10 pounds for each of its 20 square inches of area, or 200 pounds (10 x 20). In this case, the original force has been  multiplied  tenfold  while  using  the  same  pressure in  the  fluid  as  before.  In  any  system  with  these dimensions, the ratio of output force to input force is always  10  to  1  regardless  of  the  applied  force;  for example, if the applied force of the input piston 1 is 50 pounds, the pressure in the system is increased to 25 psi. This will support a resistant force of 500 pounds on the output piston 2. The system works the same in reverse. Consider piston 2 as the input and piston 1 as the output; then the output force will always be one-tenth the input force. Sometimes  such  results  are  desired. Therefore,  the  first  basic  rule  for  two  pistons  used in a fluid power system is the force acting on each is directly proportional to its area and the magnitude of each force is the product of the pressure and its area,  is totally  applicable. Volume and Distance Factors In the systems shown in views A and B of figure 10-1, the pistons have areas of 10 square inches. Since the areas of the input and output pistons are equal, a force of 100 pounds on the input piston will support a resistant  force  of  100  pounds  on  the  output  piston.  At this point, the pressure of the fluid is 10 psi. A slight force, in excess of 100 pounds, on the input piston will increase  the  pressure  of  the  fluid,  which  will,  in  turn, overcome the resistance force. Assume that the input piston is forced downward 1 inch. This displaces 10 cubic   inches   of   fluid.   Since   liquid   is   practically incompressible, this volume must go some place. In the case of a gas, it will compress momentarily but will eventually expand to its original volume at 10 psi. This is provided, of course, that the 100 pounds of force is still acting on the input piston. Thus this volume of fluid moves  the  output  piston.  Since  the  area  of  the  output piston is likewise 10 square inches, it moves 1 inch upward to accommodate the 10 cubic inches of fluid. The pistons are of equal areas; therefore, they will move equal distances, though in opposite directions. Applying this reasoning to the system in figure 10-2, it is obvious that if the input piston 1 is pushed down 1 inch,  only  2  cubic  inches  of  fluid  is  displaced.  The output piston 2 will have to move only one-tenth of an inch  to  accommodate  these  2  cubic  inches  of  fluid, because its area is 10 times that of the input piston 1. This leads to the second basic rule for two pistons in the same fluid power system, which is  the distances moved are  inversely  proportional  to  their  areas. While the terms and principles mentioned above are not all that apply to the physics of fluids, they are sufficient to allow further discussion in this training manual.  It  is  recommended  that   Fluid   Power, NAVEDTRA 12964 (latest edition), be studied for a more  detailed  and  knowledgeable  coverage  of  the physics  of  fluids  and  basic  hydraulic/pneumatic systems. COMPONENTS Since fluids are capable of transmitting force and at the same time flow easily, the force applied to the fluid atone point is transmitted to any point the fluid reaches. Hydraulic and pneumatic systems are assemblies of units capable of doing this. They contain a unit for generating force (pumps), suitable tubing and hoses for containing and transmitting the fluid under pressure, and units in which the energy in the fluid is converted to mechanical  work  (cylinders  and  fluid  motors).  In addition,  all  operative  systems  contain  valves  and restrictors to control and direct the flow of fluid and limit the  maximum  pressure  in  the  system. Because   of   the   similarities   of   hydraulic   and pneumatic systems (that is, from a training point of view), only the components of hydraulic systems are covered in this section. Remember that most of the information  is  also  applicable  to  pneumatic  systems  and their  components. PUMPS The heart of any hydraulic system is its pumps; it is the  pump  that  generates  the  force  required  by  the actuating mechanisms. The pump causes a flow of fluid; thus, the amount of pressure created in a system is not controlled  by  the  pump  but  by  the  workload  imposed  on the  system  and  the  pressure-regulating  valves. Basically, pumps may be classified into two groups based on performance: (1) fixed delivery when running 10-3