KIT- 20R0742 - Caterpillar

Power Transmission
Because hydraulic fluids are virtually incompressible, once the hydraulic system is filled with fluid it can instantly transmit power from one area to another. This does not mean that all hydraulic fluids are equal and will be able to transmit power with the same efficiency. Choosing the correct hydraulic fluid depends on the application and the operating conditions.Lubrication
Hydraulic fluid must lubricate the moving parts of the hydraulic system. The rotating components or sliding components must be able to function without touching other surfaces. The hydraulic fluid must maintain a thin film between the two surfaces in order to prevent friction, heat, and wear.Sealing
Many hydraulic components are designed to use hydraulic fluid instead of mechanical seals within the component. The viscosity of the fluid helps to determine the ability to function as a seal. Cooling
When a hydraulic system develops heat, mechanical energy is transfered to hydraulic energy. Then the hydraulic system transfers hydraulic energy back to mechanical energy. As the fluid moves throughout the system, heat flows from the warmer components to the cooler fluid. The fluid gives up the heat to the reservoir or to the coolers that are designed to maintain fluid temperatures within design limits.The following items are other properties that are expected of the hydraulic fluids:
Prevention of rust and corrosion on metal parts
The resistance to foaming and oxidation
The ability to separate air
The ability to separate water
The ability to separate other contaminates from the fluid
The ability to maintain stability over a wide range of temperatures
Illustration 1 g01061729
Controlling Hydraulic Oil Temperature
As hydraulic components work, heat builds up in the oil. Many lower pressure hydraulic systems are able to dissipate the heat through lines, through cylinders, through tanks, and other component surfaces in order to control the oil temperature. Most high pressure hydraulic systems require an oil cooler, in addition to the other components, in order to control the oil temperature.There are two types of hydraulic oil coolers that are used on mobile equipment:
Air to oil (shown on the left) where the oil passes through tubes covered with fins. A fan or a machine speed will blow air over the tubes and the fins in order to cool the oil.
Water to oil (shown on the right) is where the oil passes through a bundle of tubes. Engine cooling water will pass around the tubes in order to cool the oil.Hydraulic oil temperature must normally be maintained below 100 °C (212 °F) in order to prevent damage to components. Oil above this temperature causes seals to deteriorate. The oil also becomes thin enough to allow metal to metal contact between moving components in the system.Viscosity
Viscosity is the measurement of a fluid's resistance to flow at a specific temperature. A fluid which flows easily has a low viscosity. A fluid which does not flow easily has a high viscosity. A fluid's viscosity is affected by temperature. When a fluid becomes warmer, the fluid's viscosity becomes lower. Likewise, when a fluid cools, the viscosity increases. Vegetable oil is a very good