【文章內(nèi)容簡介】 mitless quantities because fluid systems are not so limited by the physical limitations of materials as are the electrical systems. For example, the performance of an electromang is limited by the saturation limit of steel. On the other hand, the power limit of fluid systems is limited only by the strength capacity of the material. Industry is going to depend more and more on automation in order to increase productivity. This includes remote and direct control of production operations, manufacturing processes, and materials handling. Fluid power is the muscle of automation because of advantages in the following four major categories. and accuracy of control. By the use of simple levers and push buttons, the operator of a fluid power system can readily start, stop, speed up or slow down, and position forces which provide any desired horsepower with tolerances as precise as one tenthousandth of an inch. of force. A fluid power system(without using cumbersome gears, pulleys, and levers) can multiply forces simply and efficiently from a fraction of an ounce to several hundred tons of output. force or torque. Only fluid power systems are capable of providing contant force or torque regardless of speed changes. This is acplished whether the work output moves a few inches per hour, several hundred inches per minute, a few revolutions per hour, or thousands of revolutions per minute. , safely, economy. In general, fluid power systems use fewer moving parts than parable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This, in turn, maximizes safety, panctness, and reliability. For example, a new power steering control designed has made all other kinds of power systems obsolete on many offhighway vehicles. The steering unit consists of a manually operated directional control valve and meter in a single body. Because the steering unit is fully fluidlinked, mechanical linkages, universal joints, bearings, reduction gears, etc, are eliminated. This provides a simple, pact system. In addition, very little input torque is required to produce the control needed for the toughest applications. This is important where limitations of control space require a small steering wheel and it bees necessary to reduce operatot\r fatique. Additonal benefits of fluid power systems include instantly reversible motion, automatic protection against overloads, and infinitely variable speed control. Fluid power systems also have the highest horsepower per weight ratio of any known power source. In spite of all these highly desirable features of fluid power, it is not a panacea for all power transmission problems. Hydraulic systems also have some drawbacks. Hydraulic oils are messy, and leakage is impossible to pletely eliminate. Also, most hydraulic oils can cause fires if an oils occurs in an area of hot equipment. Pneumatic System Pneumatic systems use pressurized gases to tansmit and control power. A s the name implies, pneumatic systems typically use air(rather than some other gas) as the fluid medium because air is a safe, lowcost, and readily available fluid. It is particularly safe in environments where an electrical spark could ignite leaks from system ponents. In pneumatic systems ,pressors are used to press and supply the necessary quantities of air. Compressors are typically of the piston, vane or screw type. Basically a pressor increases the pressure of a gas by redu