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 of the input force.

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 3-4, 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, in turn, overcomes the resistance force. Assume that the output piston is forced downward 1 inch. This action displaces 10 cubic inches of fluid (1 in. x 10 sq. in. = 10 c u b i c i n c h e s ) . S i n c e l i q u i d i s p r a c t i c a l l y incompressible, this volume must go some place. 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 the same distance, though in opposite directions.

Applying this reasoning to the system in figure 3-5, 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 move only one tenth of an inch to accommodate these 2 cubic inches of fluid, because its area is 10 times that of 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 (TRAMAN). The TRAMAN,

Fluid Power, NAVEDTRA 12964, should be obtained and studied for more comprehensive coverage of this subject.

TYPES OF HYDRAULIC FLUIDS

There have been many liquids tested for use in hydraulic systems. Currently liquids being tested include mineral oil, water, phosphate ester, water- based ethylene glycol compounds, and silicone fluids. The three most common types of hydraulic fluids are petroleum-based, synthetic fire-resistant, and water- based fire-resistant.

Petroleum-Based Fluids

The most common hydraulic fluids used in hydraulic systems are the petroleum-based oils. These fluids contain additives to protect the fluid from oxidation, to protect the metals from corrosion, to reduce the tendency of the fluid to foam, and to improve the viscosity.

Synthetic Fire-Resistant Fluids

Petroleum-based oils contain most of the desired traits of a hydraulic fluid. However, they are flammable under normal conditions and can become explosive when subjected to high pressures and a source of flame or high temperatures. Nonflammable synthetic liquids have been developed for use in hydraulic systems where fire hazards exist. These synthetic fire-resistant fluids are phosphate ester fire- resistant fluid, silicone synthetic fire-resistant fluid. and the lightweight synthetic fire-resistant fluid.

Water-Based Fire-Resistant Fluids

The most widely used water-based hydraulic fluids may be classified as water-glycol mixtures and water-synthetic base mixtures. The water-glycol mixture contains additives to protect it from oxidation, corrosion, and biological growth and to enhance its load-carrying capacity.

Fire resistance of the water mixture depends on the vaporization and smothering effect of steam generated from the water. The water in water-based fluids is constantly being driven off while the system is operating. Therefore, frequent checks are required to maintain the correct ratio of water to base mixture.

HYDRAULIC SYSTEM COMPONENTS

An arrangement of interconnected components is required to transmit and control power through pressurized fluid. Such an arrangement is commonly referred to as a system. The number and arrangement of the components vary from system to system, depending on application. In many applications, one main system supplies power to several subsystems, which are commonly referred to as circuits. The complete system may be a small compact unit; more often, however, the components are located at widely separated points for convenient control.

The basic components of a fluid power system are essentially the same, regardless of whether the system