NUT 0120375 - Caterpillar

Sudden movement of the machine or the release of oil under pressure can cause personal injury. At operating temperature, the hydraulic oil is hot and under pressure. Hot oil can cause burns. To prevent possible personal injury, release the pressure in all of the implement circuits before any hydraulic lines or components are disconnected or removed.
1. Release the pressure in the hydraulic system as follows:a. Move the machine to a smooth horizontal location. Move away from working machines and personnel.b. Permit only one operator on the machine. Keep all other personnel either away from the machine or in view of the operator.c. Move the switch for the CUSHION-HITCH to the "LOCKDOWN" position. Be sure the rear bracket assembly of the hitch is down against (resting on) the front hitch assembly.d. Activate the parking and secondary brakes. Lower the bowl to the ground. Lower the apron. Stop the engine.e. Move all scraper control levers to all positions to release the pressure in the hydraulic system.f. Carefully loosen the fill cap on the hydraulic oil tank to release the pressure in the tank.g. Be sure all hydraulic pressure is released before any fittings, hoses or components are loosened, tightened, removed or adjusted. Wait at least five minutes after the machine is turned off. 2. Disconnect four hose assemblies (1) from the blocker valve.3. Remove two bolts (2), the washers and blocker valve (3) from the elevator hydraulic pump.4. Remove the seal used between the blocker valve and the elevator hydraulic pump. The following steps are for the installation of the blocker valve.5. Check the condition of the O-ring seals and seal used for the installation of the blocker valve. If any of the seals are damaged, use new parts for replacement.6. Install blocker valve (3) in the reverse order of removal.7. Check the oil level in the hydraulic oil tank. If necessary, fill the hydraulic oil tank with oil to the correct level. For the correct filling procedure, see the Operation & Maintenance Manual for 623F Elevating Wheel Tractor-Scrapers, SEBU6720.Disassemble & Assemble Blocker Valve
Start By:a. remove blocker valve1. Be sure the blocker valve is thoroughly clean prior to disassembly.
There is spring force behind plug (1). When plug (1) is removed, the spring force will be released. To prevent possible personal injury, retain plug (1) while it is slowly being loosened.
2. Note the position of the fitting in plug (1). Remove the fitting from the plug. While retaining plug (1), slowly loosen it to release the spring force behind it. Remove plug (1) and spring (3) from the valve body. Remove O-ring seal (2) from the plug. 3. Turn the valve body around. Note the position of the fitting in plug (4). Remove the fitting from the plug. Remove plug (4) and stem (6) from the valve body. Remove O-ring seal (5) from the plug. Remove O-ring seal (7) from the valve body. The following steps are for the assembly of the blocker valve.4. Be sure all parts of the blocker