SEAL 0627693 - Caterpillar

Procedure for Releasing Air Pressure
When the main pumps have been serviced or the hydraulic oil has been replaced, remove the air from the main pumps. Remove the air from the main pumps in the following manner:
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat® products.Dispose of all fluids according to local regulations and mandates.
To avoid system damage, make sure that the hydraulic pump is properly filled with hydraulic oil before start-up.
Illustration 1 g00563367
Pump compartment
While the engine is stopped, remove vent plug (1) on the top of the main hydraulic pump.
Leave vent plug (1) out of the pump for several minutes until the main pumps are filled with hydraulic oil. After the pumps fill with oil, install vent plug (1). Tighten vent plug (1).
Start the engine.
Run the engine at low idle speed. Raise the boom and hold the boom in this position.
Stop the engine. Slowly lower the boom until the bucket contacts the ground. This pressurizes the hydraulic oil tank.
Slowly loosen vent plug (1) until oil begins to flow from the opening. This indicates that air has been completely purged from the main hydraulic pump.
Tighten vent plug (1) to the specified torque.