ENGINE AR-COMPLETE 4237852 - Caterpillar

Illustration 1. Location of HPC valves in former HPC controlled main hydraulic pump and hydraulic schematic.
Illustration 2. New non-HPC controlled main hydraulic pump and hydraulic schematic.Adaptable To: The new non-HPC controlled 1R8930 Main Hydraulic Pump replaces the former HPC controlled 857441 Main Hydraulic Pump on E110B Excavators 8MF249-Up and is adaptable to all earlier E110B Excavators. The new non-HPC controlled 1R8928 MainHydraulic Pump replaces the former HPC controlled 855799 Main Hydraulic Pump on E120B Excavators 6JF466-Up and is adaptable to all earlier E120B Excavators. The former pumps are canceled.When a former HPC controlled main hydraulic pump isreplaced with a new non-HPC controlled pump, adjust the main relief valve for a pressure decrease. See the appropriate Reference.
When a former HPC controlled main hydraulic pump is not replaced with a new non-HPC controlled pump, but the elimination of HPC control is desired:
1. Loosen locknut (1) on HPC adjusting screw (2) on both pumps. See Illustration 3. Turn the adjusting screws one turn clockwise. Tighten the locknuts.2. Adjust the main relief valve for a pressure decrease. See the appropriate Reference.
Location of HPC adjusting screw (2) and locknut (1).The elimination of the HPC control increases the pump flow in the high pressure area. Therefore, the main relief valve is adjusted to keep the main system pressure the same value regardless of the increased flow. See Chart A.
The elimination of the HPC control changes some of the specifications in the operations test. See Chart B.
Charts C and D list the new and former pump flow specifications for the E110B and E120B Excavators respectively.