PR-275 PAVEMENT PROFILER General Caterpillar


Before operating the PR-275-RT the first time, study the first two sections of this manual and become familiar with the machine, its systems and its controls. Actuate the various controls to be sure that no confusion exists as to what the lever or switch controls and what will happen when it is actuated.

When operating the PR-275-RT keep in mind that the cutter and the wheels are powered through hydrostatic transmissions. The hydrostatic transmission transmits the power generated by the engine to the cutter or wheels by pressurized hydraulic oil flow rather than by mechanical linkage. The engine turns the hydrostatic pump through a gearbox. The oil from the pump powers the motor which is linked to the load through a gearbox or gear reducer.

The amount of power transmitted by the hydrostatic transmissions depends on the volume of oil flowing to the motor and on the pressure of the oil. The same power can be transmitted with an infinite combination of flow rates and pressures; i.e., the same power can be transmitted at a high flow and low pressure as at a low flow and high pressure. However, certain flow and pressure combinations will provide longer system life.

The hydrostatic transmission uses system oil for cooling and lubrication purposes. The amount of oil provided for cooling purposes by the charge pump is determined directly by engine speed since the charge pump is driven at pump shaft speed; the greater the engine speed, the greater the amount of cooling oil provided.

The lubricating properties of the hydraulic oil in the system, as with any lubricating oil, vary according to the temperature of the oil with the best lubrication of the system provided when the oil is at the normal operating temperature. When the oil temperature is above normal the oil does not lubricate the system as well, which causes more heat. Prolonged operation of the oil at high temperatures causes the oil to break down and lose even more of its lubricating ability.

Operation of the system at a high pressure and low flow to provide a given amount of power produces more heat than operation at a high flow and low pressure to produce the same power. At the same time, the amount of cooling oil provided by the charge pump is reduced and the stress on the system components (pump, motor, lines, etc.) is increased. It is only logical that the best system cooling, lubrication and stress conditions, and therefore the longest system life, are provided by operating the system at the lowest pressure and the greatest flow that will do the job.

To be sure of the longest, most trouble free life for the hydrostatic transmissions: