TUBE AS 3967622 - Caterpillar

All pump lines and pump housing must be filled with oil prior to start-up. Failure to provide proper oil fill may result in system damage.
Illustration 1 g00294533
Pump Compartment (1) Vent plug.
When the engine is stopped, remove vent plug (1) from the top of the main pump. Leave vent plug (1) out for several minutes until the main pumps are filled with hydraulic oil. When the pumps are filled with oil, tighten vent plug (1) and start the engine.
Run the engine at low idle. Raise the boom and hold the boom in the RAISED position.
Stop the engine. Lower the boom slowly until the bucket is on the ground. The hydraulic tank is now under pressure.
Slowly loosen vent plug (1) . Loosen vent plug (1) until hydraulic oil flows out of the opening for vent plug (1) .
Tighten vent plug (1) .Note: If the machine has boom lowering control valves, hydraulic oil pressure can accumulate in the boom cylinder lines group. For information on relieving the hydraulic oil pressure, refer to Systems Operation, "Lowering Control Valve (Boom)".