HOUSING-FLYWHEEL 2051229 - Caterpillar

1 The purpose of oil The main purpose of hydraulic fluid is to transfer power from the pump to the actuators but it must also perform many other tasks which are critical to a well designed system.First the oil must have good lubricity or be "slippery" so that the friction will be as low as possible to keep metal to metal wearing at a minimum.Second, the viscosity or "thickness" must be in the proper range at the operating temperature so that unwanted leakage will be at a minimum, but will still allow oil to lubricate the close fitting parts in the system. (Oil that is too thin will leak past seals, valve spools and the gears; oil that is too thick will not flow properly and cause the pump to cavitate or starve.)Third, the oil must be compatible with the seals used in the system.Fourth, there should also be additives in the oil to slow down the effects of rust, oxidation (oxygen in the air combining with the oil to form sludge) foaming, and water settling to the bottom of the reservoir.Fifth, the oil must be able to pour or flow at the lowest expected temperature so that the oil can reach or get into the pump.For all of the reasons listed, automatic transmission fluid (ATF) was found in most cases, to be the best readily available fluid for the job in most climate conditions.2. Selecting fluids for applications outside of ATF's temperature range. When looking for fluids that can be used in the place of automatic transmission fluid or for applications where the operating temperature is outside of the range of automatic transmission fluid the following specifications should be discussed with your local oil distributor.A. Fluid must be compatible with Buna-N sealing compounds.B. The Pour Point must be below the lowest anticipated temperature that will be encountered.C. It should contain Rust and Oxidation as well as other detergent type inhibitors.D. The Viscosity (SUS) should lie between 80 as a minimum and 375 as a maximum in the operating range, with the ideal viscosity near 200 SUS.E. The viscosity index should be as high as possible.As an example, automatic transmission fluid (ATF) has the following specifications as listed by most oil manufacturers.A. Viscosity (SUS) 37,8 °C 185 - 20598,9 °C 45 - 55B. Pour Point -42 - -37°CC. Viscosity Index 145 - 165 In an emergency, for cold weather applications SAE 10W non-detergent oil mixed by volume with no more than 30% #1 fuel oil or kerosene can be used.Pump priming
New system installations, as well as those that are disassembled for repair, require proper priming to avoid possible pump failure. A pump is said to be "primed" when the internal cavity is full of oil and the air has been expelled.Prime a pump as follows:1. "Crack" or remove the high pressure line at or near the cylinder.2. Operate the unit until oil flow is clear. (Air is absent).3. Retighten or replace hose.Water in the oil
Water can enter the