HYDRAULICS
1.1
DESCRIPTION AND OPERATION DESCRIPTION General The hydraulic system supplies the power for boom manipulation, attachments, brakes and steering. A hydraulic oil reservoir has a filter breather cap and supplies the main and auxiliary hydraulic pumps. The reservoir is also fitted with a sight gauge. With the boom in the lower position, retracted and with the carriage tilted forward, the oil level will be visible in the gauge above the red line.
Dumping (dissipation) of hydraulic pressure Always dump all hydraulic pressure from the system before servicing any hydraulic component. Ensure there is sufficient space and headroom around machine before operating any hydraulic control.
To dump brake system pressure The main hydraulic pump is driven from the engine gearbox and is of the variable displacement type. Pressurized oil from the hydraulic pump is directed to the hydraulic control valve assembly (PVG). The control valve is modular in construction and combines individual sections (slices), each with a different use. At one end of the control valve is the priority module (PVSP), which controls the supply of hydraulic oil to the steering and brake systems. The remaining oil is supplied to those sections of the control valve that control each boom service. The brakes, steering and boom services each supply a load-sensing signal, hydraulically, to the main hydraulic pump. This maintains the optimum supply of oil to those services. The auxiliary hydraulic pump is driven by the engine timing case gears and supplies pressurized oil to the motor of the engine cooling fan. It also supplies oil to the front axle parking brake units, to keep the parking brake off. When this hydraulic pressure is released, spring pressure applies the parking brake. The hydraulic tank is divided into clean and dirty sides by a mesh filter. A low-pressure filter is installed in the oil supply to the cooling fan system. This filter constantly filters the hydraulic fluid and a blockage indicator, installed in the filter, operates a warning light in the cab when servicing is required. Modifications, such as the introduction of a reverse cooling fan or different brake servo valves, will change the basic layout of the system. To obtain the correct component layout you must refer to the applicable schematic illustration, which can be located using the batch Serial Number (S/No.) for the particular machine.
1. Stop the engine. 2. Make sure the machine is parked on firm and level ground and chock the wheels. 3. Turn the ignition switch to position (1). 4. Set the parking brake switch, if necessary, to the parking brake applied position. 5. Press the brake pedal repeatedly until the brake charge warning lamp illuminates. 6. Press the brake pedal a further twenty times to ensure that residual pressure in the brake system is fully dissipated. 7. Turn the ignition switch to off.
To dump a system pressure NOTE: This procedure applies to all machine hydraulic systems, except brakes. 1. Stop the engine. 2. Make sure the machine is parked on firm and level ground and chock the wheels. 3. Turn the ignition switch to position ‘I’. 3. Operate the applicable system until all hydraulic pressure has been dissipated. 4. Turn the ignition switch to off.
