BODY 2S3536 - Caterpillar

Procedure To Purge Air From Hydraulic Pumps
Do not start the engine until the pump has been filled with hydraulic oil. Not enough oil can result in serious damage to hydraulic components.
When the hydraulic oil has been replaced, remove air from the hydraulic system as follows:
Illustration 1. Air vent plug for hydraulic pump.1. With the engine stopped, remove the air vent plug on top of the pump. See Illustration 1.2. Add oil into the pump through the vent plug. When the pump is filled with hydraulic oil, install the vent plug and start the engine.3. Loosen the fill plug for the hydraulic tank. With the engine at low idle, fully raise the boom and hold it in this position.4. Tighten the fill plug and slowly lower the boom with the stick in a vertical position until the bucket is on the ground. Stop the engine. This pressurizes the hydraulic tank.
Illustration 2. Position of machine before procedure to bleed air from hydraulic pumps.5. Slowly loosen the air vent plug several turns until oil flows out of the plug opening. This indicates that air has been purged from the pump. Retighten the plug.6. Close the access door.7. Start and operate the engine at any (no load) idling speed for five minutes.8. Operate the control levers to allow the hydraulic oil to circulate through all hydraulic circuits. Lower the bucket to the ground with the stick vertical to the ground. Stop the engine.
Illustration 3. Check oil level with hydraulic tank sight gauge.9. Maintain the oil level between the marks on the sight gauge in the appropriate temperate range. Always dispose of used oil and filters as established by local regulations.This procedure is not included in all Disassembly and Assembly modules in Service Manuals for the machines. It is recommended that a copy of this article be inserted in all Disassembly and Assembly modules for reference.