Pilot Oil Supply Circuit

Pilot Oil Supply Circuit Introduction Pilot system oil output from pilot pump (42) has the following three main functions: 1. To control main pump output. 2. To provide easier operation of control levers. 3. To create pilot pressure signals so various controls can be achieved. The pressure of pilot system oil is limited to 3450 kpa (500 psi) by pilot relief valve (34). Pilot system oil from pilot pump (42) goes through pilot filter (55) and line (52) and enters pilot oil manifold (46). The pilot oil is then separated into the following circuits through respective passages (43), (47) and (51): 1. Power mode valve circuit; Pilot oil from passage (51) goes to power mode solenoid valve (33). The pilot oil is changed into a hydraulic signal of power shift pressure. The hydraulic signal goes through line (40) to the main pump regulator to control the pump output. NOTE: For more information, see the section, "Main Pumps" section, in this module. 2. Pilot control valve circuits; The pilot control valve is the main component in the pilot system. The pilot oil in passage (43) goes through line (50) to hydraulic activation control valve (53). The pilot oil then goes to pilot control valves (25), (27) and (28) through respective pilot lines. When a pilot control valve is

operated, pilot oil goes to main control valve(s) selected. The pilot oil shifts the stem(s) in the selected control valve(s) to operate a cylinder and/or motor. The following is a typical example: If the boom control lever is moved to the BOOM RAISE position, pilot oil from line (29) shifts the stem in boom I control valve (14) up. If the boom control lever is moved to the BOOM LOWER position, pilot oil from line (5) shifts the boom I control valve stem down. When the boom control levers are moved to either the BOOM LOWER or STICK IN positions, pilot oil from line (6) or (24) shifts spools (18) or (23) to activate boom drift reduction valve (16) or stick drift reduction valve (19). NOTE: For more information on the stick/boom drift reduction valve, see the section, "Stick In Control" and "Boom Lower Control", in this module. When the boom control lever is moved for trenching operation with swing priority solenoid valve (32) energized, pilot oil from boom pilot control valve (28) goes through shuttle valve (31), swing priority solenoid valve (32) and line (36) to spool (parallel/tandem switch) (21). Spool (21) activates assuring optimum boom and stick speeds for exact trenching operation. NOTE: For more information on a trenching operation, see the section, "Trenching Operation" in this module. 3. Pilot circuits in the main control valves; Pilot oil from passage (47) goes through line (30) to main control valves (10). The oil then separates into two oil flows through passages (9) and (22). When the main control valves are in the neutral position, oil pressure in both passages (9) and (22) remains low. When the travel control is operated, oil pressure in passage (9) increases. When swing or implement control is activated, oil pressure in passage (22) increases. a. Pilot oil from passages (9) and (22) goes through respective lines (39) and (37) to shuttle valve (44). The pilot oil then goes through line (38) to spool (main pump load signal) (48). When no hydraulic control is activated, oil pressure from line (38) does not activates spool (48), allowing pilot oil flow from line (54) through spool (48) to the pump regulator. This causes the main pump to destroke. When a hydraulic control is activated, increased oil pressure from line (38) activates spool (48) blocking the oil flow from line (54) to the pump regulator. The main pump does not destroke but provides normal output flow. b. When all pilot control valve levers are in the NEUTRAL position, oil pressure in line (38) remains low and does not activate pressure switch (45). This allows for the one touch low idle control system to activate. NOTE: For further information on one touch low idle control, see the separate module, "Electric System, Systems Operation" module. c. When an implement or swing control is activated, increased oil pressure from passage (22) activates selector valve (11) allowing main relief valve (17) to open at the specified relief valve pressure setting for implement/swing operation. When travel control is activated alone, oil pressure in passage (20) increases allowing the main relief valve to open at the specified relief valve pressure setting for travel operation. NOTE: For further information on the main relief valve, see the section "Main Control Valves" in this module.

d. When the travel pilot control valve is activated simultaneous with the swing or implement pilot control valves, pilot oil in passage (22) is directed through passage (13) to straight travel control valve (14). Straight travel control valve (14) activates so the machine can travel straight. NOTE: See "Straight Travel Control" for more information. 4. Swing parking brake release circuit; The swing parking brake release circuit releases the swing parking brake during implement and/or swing operation. Pilot oil in passage (47) goes through line (4) to swing parking brake control valve (2). Pilot oil in passage (22) also goes through line (3) to the safety lock valve (56) to swing parking brake control valve (2). When implement and/or swing controls are operated, the pilot oil pressure in passage (22) increases. The pressure increase activates swing parking brake control valve (2) to the open position. Now the pilot oil from line (4) goes through swing parking brake control valve (2) to swing parking brake (1). This releases the swing parking brake. NOTE: For more information, see "Swing Control" section in this module. Components In Pilot Oil Circuit Pilot Oil Circuit Schematic (Partial) (1) Pilot control valve (stick/swing). (2) Pilot control valve (bucket/boom). (3) Accumulator. (4) Pilot relief valve. (5) Right pump. (6) Left pump. (7) Pilot pump. (8) Hydraulic activation control valve. (9) Pilot oil manifold. (10) Pilot filter. This section gives the description on the construction and operation of the following pilot circuit components: 1. Pilot pump (7). 2. Pilot filter (10). 3. Accumulator (3). 4. Pilot relief valve (4).

5. Hydraulic activation control valve (8). 6. Pilot control valves for stick/swing (1) and bucket/boom (2). (See "Travel Control" for the pilot control valves.) Pilot Pump Pilot pump (7) is a gear type pump. It is mechanically connected to the main pump in series. The pilot pump supplies pressure oil to the pilot system. The maximum pilot pump output flow at no-load is approximately 16 liters/min. (4.2 U.S.gpm). Pilot Filter Pump Compartment (3) Accumulator. (4) Pilot relief valve. (9) Pilot oil manifold. (10) Pilot filter.

Pilot Filter (10) Pilot filter. (11) Relief valve. (12) Filter element. Filter element (12) in pilot filter (10) removes contaminants from the pilot oil. If the oil flow through filter element (12) becomes restricted due to oil being too cold or too contaminated, the oil bypasses pilot filter (10) through bypass relief valve (11).

Accumulator And Pilot Relief Valve Pilot Oil Manifold (Partial) (3) Accumulator. (4) Pilot relief valve. (9) Pilot oil manifold. (13) Gas chamber. (14) Bladder. (15) Bowl. (16) Oil chamber. (17) Passage. (18) Check valve. (19) Inlet port. (20) Passage. (21) Valve. Pilot oil flows through pilot filter (10), pilot oil manifold (9) and passage (20). The pilot oil opens check valve (18) and goes out through passage (17) to hydraulic activation control valve (8). Pilot oil then goes to the pilot control valves. Accumulator (3) provides oil to the pilot line as makeup oil. During combined operations, the pilot system requires more oil because there is not enough pilot pump oil flow. When lowering implements with the engine stopped, makeup pressure oil supply is provided by the accumulator. The accumulator stores hydraulic oil pressure by taking advantage of the compressibility of nitrogen gas in gas chamber (13). The pilot pump oil from passage (20) goes through inlet port (19) and into oil chamber (16). The pilot pressure oil pushes against bladder (14) compressing the nitrogen gas in gas chamber (13).

Check valve (18) is located in the passage connected to inlet port (19). The check valve prevents pressure oil from flowing back to passage (20). Accumulator oil goes through passage (17) and is used to shift the main control valve stems. Pilot relief valve Pilot relief valve (4) is attached to pilot oil manifold (9). The pilot relief valve limits the pressure in the pilot circuit to 3450 kpa (500 psi). When the pressure in passage (20) increases to the pilot relief valve pressure setting, valve (21) opens to allow part of oil in passage (20) to drain to the hydraulic tank. Hydraulic Activation Control Valve Cab Floor (Bottom View) (1) Hydraulic activation control valve. Cab (2) Hydraulic activation control lever (LOCKED position).

Cab (2) Hydraulic activation control lever (UNLOCKED position). Hydraulic activation control valve (1) is part of the pilot control valve circuit. When hydraulic activation control lever (2) is placed in the LOCKED position, hydraulic activation control valve (1) closes to block pilot pump oil supply to the pilot control valves. All hydraulic controls are blocked. No operation of cylinders and motors can be made by activation of hydraulic controls. Hydraulic activation control valve (1) has a limit switch. The limit switch allows the engine start switch to operate only when hydraulic activation control lever is in the LOCKED position. This prevents unexpected machine and/or implement operation. When hydraulic activation control lever (2) is placed in the UNLOCKED position, hydraulic activation control valve (1) is opened to allow pilot oil to flow the pilot control valves. Hydraulic Activation Control Valve (unlocked position). (1) Hydraulic activation control valve. (3) Return port. (4) Port. (5) Limit switch. (6) Port (pilot control valve for swing/stick). (7) Port (pilot control valve for bucket/boom). (8) Port (pilot control valve for left travel). (9) Port (pilot control valve for right travel). (10) Passage. (11) Passage. (12) Spool. (13) Passage. (14) Return passage.

Cross Section Of Hydraulic Activation Control Valve (1) (4) Port. (5) Limit switch. (10) Passage. (11) Passage. (12) Spool. (15) Plunger. (16) Notch. When hydraulic activation control valve (1) is placed in the LOCKED position, port (4) is open to passage (10) through passage (11). Pilot oil enters hydraulic activation control valve (1) through port (4). The pilot oil then goes through passage (10) and out through ports (6), (7), (8) and (9) to pilot control valves. The pilot oil then activates the main control valves. Limit switch (5) is located in hydraulic activation control valve (1). When hydraulic activation control valve (1) is in the UNLOCKED position, spool (12) in hydraulic activation control valve (1) is held at the position shown by the unlocked position section view in the previous illustration. In this position, plunger (15) of limit switch (5) moves out to the left until its end seats in notch (16). Limit switch (5) is now in the Off position. When hydraulic activation control valve (1) is in the LOCKED position, spool (12) turns to move plunger (15) to the right. The plunger moves to the right turning limit switch (5) On. Pilot pump oil is blocked (held) between port (4) and passage (11). Passage (13) is now connected to return passage (14) within spool (12). When the flow of pilot pump oil is blocked to passage (10), return oil from each pilot control valve goes through passages (10), (13) and (14). Return oil now passes through return port (3) to the pump suction line. Movement of the pilot control valve levers will not activate the main control valves. The engine start switch can only be operated when limit switch (5) is in the On position and hydraulic activation control valve (1) is in the LOCKED position.

Pilot Control Valves Cab (1) Pilot control valve (stick/swing). (2) Pilot control valve (bucket/boom). Main Control Valve Compartment (Top View) (3) Pilot line (stick I in). (4) Pilot line (swing left). (5) Pilot line (forward right travel). (6) Pilot line (forward left travel). (7) Pilot line (boom I lower). (8) Pilot line (bucket close). (9) Pilot line (stick II out). Both pilot control valves contain within them four valves. Pilot control valve (1) controls the stick in and out movement and the right and left swing movement. Pilot control valve (2) controls the boom raise and lower movement and bucket open and close movement. Pilot control valves (1) and (2) send pilot pump oil to the main control valves through the following pilot lines: Pilot line (3) for stick I in. Pilot line (4) for left swing. Pilot line (7) for boom I lower. Pilot line (8) for bucket close. Pilot line (9) for stick II out. Pilot lines for stick I out, right swing, boom I raise, bucket open, and boom II raise are connected opposite their corresponding ports on the main control valves, respectively.

Pilot Control Valve (Implement And Swing) (1) Control lever. (2) Plate. (3) Rod. (4) Seat. (5) Metering spring. (6) Spring. (7) Return passage. (8) Passage. (9) Passage. (10) Passage. (11) Spool. (12) Rod. (13) Return passage. (14) Passage. (15) Passage. (16) Passage. (17) Passage. (18) Port. (19) Port. (20) Pilot pump. When control lever (1) is moved to the left, plate (2) tilts to the left. Plate (2) pushes down on rod (3) and seat (4). Seat (4) compresses metering spring (5) and spring (6). Metering spring (5) moves spool (11) down to open passage (10). The pilot pump (20) oil from port (18) can now go through passage (10) and out through passage (9) to the main control valves. The pressure of the oil on the end of the main control valve stem causes it to move for implement or swing operation. When passage (10) is opened, passage (8) remains closed, blocking the connection between passage (9) and return passage (7). The oil at the opposite end of the main control valve stem (for operation) flows back through passages (15) and (14) to return passage (13). The oil then goes back to the hydraulic tank. When rod (12) is not pushed down, passage (16) is closed blocking the connection between passages (17) and (15). Spring (6) provides the force to return the control levers to the NEUTRAL position when released. When the pilot control lever is moved, metering spring (5) is compressed. The metering spring forces spool (11) to move down. Movement of spool (11) controls the amount of pilot oil pressure that goes through passage (10). Pilot oil passes through passage (10) to the main control valves. The pilot oil pressure sent to the main control valves changes proportionally to the travel distance of the pilot

control lever. Movement of the main control valve stem causes a change in oil flow to cylinders and/or motors, proportional to a change in pilot oil pressure. Fine movement of the pilot control lever allows fine control of operation of the cylinders and/or motors.