312F and 313F Excavator Machine Systems Return Hydraulic System Caterpillar

Illustration 1	g06015877
Partial hydraulic schematic for the return system (1) Travel motors (2) Swing motor (3) Drain line (4) Main control valve (5) Swivel (6) Drain line (7) Makeup line (8) Drain line (9) Valve (10) Center bypass passage (11) Return passage (12) Center bypass passage (13) Valve (14) Drain line (15) Orifice (16) Orifice (17) Drain line (18) Pilot manifold (19) Pilot oil distribution manifold (20) Drain line (21) Return line (22) Return block (23) Return passage (24) Boom priority valve (25) Hydraulic oil cooler (26) Bypass check valve (27) Slow return check valve (28) Boom regeneration PRV (29) Drain line (30) Return line (31) Hydraulic tank (32) Suction line (33) Case drain filter (34) Drain line (35) Idler pump (36) Pilot pump (37) Drive pump (38) Drain line

The oil from drive pump (37) and idler pump (35) enters main control valve (4). Then, the oil flows to the return passages in one of the following conditions.

1. When all joysticks and/or travel levers/pedals are in the NEUTRAL position, oil from idler pump (35) flows through center bypass passage (10) through orifice (16) to return passage (23). Oil from drive pump (37) flows through center bypass passage (12) through orifice (15) to return passage (23).

2. When any one of the joysticks and/or travel levers/pedals is shifted from the NEUTRAL position, center bypass passages (10) and (12) are blocked. The return oil from the cylinders and/or motors now flows through return passage (11).

Illustration 2	g02758201
Return system components (1) Travel motor (3) Drain line (4) Main control valve (8) Drain line (18) Pilot manifold (21) Return line (25) Hydraulic oil cooler (26) Bypass check valve (27) Slow return check valve (30) Return line (31) Hydraulic tank (32) Suction line (33) Case drain filter (35) Idler pump (36) Pilot pump (37) Drive pump (38) Drain line

The return oil from return passage (23) and return passage (11) flows through slow return check valve (27) back to hydraulic tank (31) in one of the following conditions.

1. When the oil temperature is very low, most of the oil is returned through bypass check valve (26) to hydraulic tank (31). The remainder of the oil flows into hydraulic oil cooler (25) and to hydraulic tank (31).

2. When the oil temperature increases, the rate of oil flow through bypass check valve (26) decreases. This action causes the rate of oil flow through hydraulic oil cooler (25) to increase.

Case drain oil from drive pump (37) and idler pump (35) flows into case drain line (38).

Reference: For more information concerning the bypass check valve, refer to Systems Operation, "Bypass Valve (Return)".

Illustration 3	g02758516
Return system components (view from the front) (2) Swing motor (4) Main control valve (5) Swivel (6) Drain line (7) Makeup line (8) Drain line (14) Drain line (19) Pilot oil distribution manifold (20) Drain line (22) Return block (24) Boom priority valve (28) Boom regeneration PRV (31) Hydraulic tank

Case drain oil from the left travel motor and case drain oil from the right travel motor combine and flow through swivel (5). From swivel (5) the case drain oil combines with the case drain oil from swing motor (2). Case drain oil in line (6) from the swing motor and case drain oil from the travel motors flows into drain line (8). Oil flow from drain line (8) combines with case drain line (38) from the pumps. All of the case drain oil from the pumps and the motors combine and now flow through case drain filter (33) to hydraulic tank (31).

Makeup line (7) will route return oil to the inlet port of the swing motor if a vacuum condition occurs at the swing motor during swing stop.

For more information concerning the makeup operation of the return hydraulic system at the swing motor, refer to the following sections in this manual.

• Systems Operation, "Check Valve (Return Makeup)"

• Systems Operation, "Oil Makeup (Swing System)"

• Systems Operation, "Relief Valve (Swing)"

Return oil from pilot oil distribution manifold (19) flows through drain line (20) to suction line (32). Return oil from valve (9) at the stick drift reduction valve returns to return block (22) through drain line (17). Return oil from valve (13) at the boom drift reduction valve and return oil from boom regeneration PRV (28) combine and flows through drain line (29). Return oil from the pilot logic circuit in the main control valve returns through drain line (14) to the return block (22). From drain line (29) the oil returns to return block (22). All the return oil in the return block combines and flows to suction line (32).