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STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
HYDRAULIC PUMP PC78US-6 (with blade) Serial No.: 4001 – 5500 PC78UU-6 (with blade) Serial No.: 22832 – 23500 Model: LPD45 + 45
P1 : Pump discharge P2 : Pump discharge P3 : Gear pump discharge P4 : Pilot pump discharge P5 : Gear pump pressure pickup port PD : Drain PM : PC mode changeover pressure pickup port P1T : Travel deviation adjustment orifice P2T : Travel deviation adjustment orifice
PC78US-6
PD2 : Pump drain (plug) PDA: Air bleeder PEN: Control pressure pickup port PGS: Gear pump suction PLS : LS pressure input (From control valve) PPT : PTO oil filler PS1 : Main pump suction PEPC: EPC main pressure pickup port PPLS : Pump pressure input (From control valve)
10-55 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
PC78US-6 (without blade) Serial No.: 4001 – 5500 Model: LPD45 + 45
P1 : Pump discharge P2 : Pump discharge P4 : Pilot pump discharge PD : Drain PM : PC mode changeover pressure pickup port P1T : Travel deviation adjustment orifice P2T : Travel deviation adjustment orifice PD2 : Pump drain (plug)
10-56 (10)
PDA: Air bleeder PEN: Control pressure pickup port PLS : LS pressure input (From control valve) PPT : PTO oil filler PS1 : Main pump suction PEPC: EPC main pressure pickup port PPLS : Pump pressure input (From control valve)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
T : Drain P1 : Pump discharge P2 : Pump discharge P3 : Gear pump pressure input PD : Drain PH : Pump shuttle PAV : Pump average pressure
PC78US-6
HYDRAULIC PUMP
PD2 : Drain (Plug) PDE: EPC drain PEN: Control pressure input PPT : PTO oil filler PS1 : Pump suction PEPC: EPC main pressure pickup port
10-57 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
HYDRAULIC PUMP
Shaft Flange Case Rocker cam Shoe Piston Cylinder block Valve plate Servo piston Oil seal
10-58 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
PDE: EPC drain 1. EPC valve PC valve T: Drain P3: Gear pump pressure input PH: Pump shuttle pressure PAV: Pump average pressure PPL: PC valve output pressure PEPCOUT: EPC output pressure 2. Lever 3. Spring
PC78US-6
4. Retainer 5. Seat 6. Spool 7. Sleeve 8. Piston 9. Seal 10. Piston 11. Plug
LS valve PE: Control piston pressure PH: Pump shuttle pressure PLS: LS pressure input PPL: PC valve output pressure PPLS: LS pump pressure input 12. Spool 13. Plug
14. Seat 15. Spring 16. Seat 17. O-ring 18. Backup ring 19. Nut 20. Plug
10-59 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
PC78US-6 (with blade) Serial No.: 5501 – 6500 PC78UU-6 (with blade) Serial No.: 23501 and up Model: LPD45 + 45
P1 : Pump discharge P2 : Pump discharge P3 : Gear pump discharge P4 : Pilot pump discharge P5 : Gear pump pressure pickup port PD : Drain PM : PC mode changeover pressure pickup port P1T : Travel deviation adjustment orifice P2T : Travel deviation adjustment orifice
10-60 (10)
PD2 : Pump drain (plug) PDA: Air bleeder PEN: Control pressure pickup port PGS: Gear pump suction PLS : LS pressure input (From control valve) PPT : PTO oil filler PS1 : Main pump suction PEPC: EPC main pressure pickup port PPLS : Pump pressure input (From control valve)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
T P1 P2 P3 P5 PD PH
: Drain : Pump discharge : Pump discharge : Gear pump pressure input : Gear pump pressure pickup port : Drain : Pump shuttle
PC78US-6
HYDRAULIC PUMP
PAV : Pump average pressure PD2 : Drain (Plug) PDE: EPC drain PEN: Control pressure input PPT : PTO oil filler PS1 : Pump suction PEPC: EPC main pressure pickup port
10-61 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
PC78US-6 (without blade) Serial No.: 5501 – 6500 Model: LPD45 + 45
P1 : Pump discharge P2 : Pump discharge P4 : Pilot pump discharge PD : Drain PM : PC mode changeover pressure pickup port P1T : Travel deviation adjustment orifice P2T : Travel deviation adjustment orifice PD2 : Pump drain (plug)
10-62 (10)
PDA: Air bleeder PEN: Control pressure pickup port PLS : LS pressure input (From control valve) PPT : PTO oil filler PS1 : Main pump suction PEPC: EPC main pressure pickup port PPLS : Pump pressure input (From control valve)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
T : Drain P1 : Pump discharge P2 : Pump discharge PD : Drain PH : Pump shuttle PAV : Pump average pressure PD2 : Drain (Plug)
PC78US-6
HYDRAULIC PUMP
PD3 : Drain PDE: EPC drain PEN: Control pressure input PPT : PTO oil filler PS1 : Pump suction PEPC: EPC main pressure pickup port
10-63 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
HYDRAULIC PUMP
Shaft Flange Case Rocker cam Shoe Piston Cylinder block Valve plate Servo piston Oil seal
10-64 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
PDE: EPC drain 1. EPC valve PC valve T: Drain P3: Gear pump pressure input PH: Pump shuttle pressure PAV: Pump average pressure PPL: PC valve output pressure PEPCOUT: EPC output pressure 2. Lever 3. Spring
PC78US-6
4. Retainer 5. Seat 6. Spool 7. Sleeve 8. Piston 9. Seal 10. Piston 11. Plug
LS valve PE: Control piston pressure PH: Pump shuttle pressure PLS: LS pressure input PPL: PC valve output pressure PPLS: LS pump pressure input 12. Spool 13. Plug
14. Seat 15. Spring 16. Seat 17. O-ring 18. Backup ring 19. Nut 20. Plug
10-65 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
PC78US-6 (with blade) Serial No.: 6501 and up Model: LPD45 + 45
P1 : Pump discharge P2 : Pump discharge P3 : Gear pump discharge P4 : Pilot pump discharge P5 : Gear pump pressure pickup port PD : Drain PM : PC mode changeover pressure pickup port P1T : Travel deviation adjustment orifice P2T : Travel deviation adjustment orifice
10-66 (10)
PD2 : Pump drain (plug) PDA: Air bleeder PEN: Control pressure pickup port PGS: Gear pump suction PLS : LS pressure input (From control valve) PPT : PTO oil filler PS1 : Main pump suction PEPC: EPC main pressure pickup port PPLS : Pump pressure input (From control valve)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
T P1 P2 P3 P5 PD PH
: Drain : Pump discharge : Pump discharge : Gear pump pressure input : Gear pump pressure pickup port : Drain : Pump shuttle
PC78US-6
HYDRAULIC PUMP
PAV : Pump average pressure PD2 : Drain (Plug) PDE: EPC drain PEN: Control pressure input PPT : PTO oil filler PS1 : Pump suction PEPC: EPC main pressure pickup port
10-67 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
PC78US-6 (without blade) Serial No.: 6501 and up Model: LPD45 + 45
P1 : Pump discharge P2 : Pump discharge P4 : Pilot pump discharge PD : Drain PM : PC mode changeover pressure pickup port P1T : Travel deviation adjustment orifice P2T : Travel deviation adjustment orifice PD2 : Pump drain (plug)
10-68 (10)
PDA: Air bleeder PEN: Control pressure pickup port PLS : LS pressure input (From control valve) PPT : PTO oil filler PS1 : Main pump suction PEPC: EPC main pressure pickup port PPLS : Pump pressure input (From control valve)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
T : Drain P1 : Pump discharge P2 : Pump discharge PD : Drain PH : Pump shuttle PAV : Pump average pressure PD2 : Drain (Plug)
PC78US-6
HYDRAULIC PUMP
PD3 : Drain PDE: EPC drain PEN: Control pressure input PPT : PTO oil filler PS1 : Pump suction PEPC: EPC main pressure pickup port
10-69 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
HYDRAULIC PUMP
Shaft Flange Case Rocker cam Shoe Piston Cylinder block Valve plate Servo piston Oil seal
10-70 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
PDE: EPC drain 1. EPC valve PC valve T: Drain P3: Gear pump pressure input PH: Pump shuttle pressure PAV: Pump average pressure PPL: PC valve output pressure PEPCOUT: EPC output pressure 2. Lever 3. Spring
PC78US-6
4. Retainer 5. Seat 6. Spool 7. Sleeve 8. Piston 9. Seal 10. Piston 11. Plug
LS valve PE: Control piston pressure PH: Pump shuttle pressure PLS: LS pressure input PPL: PC valve output pressure PPLS: LS pump pressure input 12. Spool 13. Plug
14. Seat 15. Spring 16. Seat 17. O-ring 18. Backup ring 19. Nut 20. Plug
10-71 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
Function • This pump converts the revolution and torque of the engine transmitted to its shaft into hydraulic energy and discharges hydraulic oil according to the load. • The discharge can be changed by changing the swash plate angle.
HYDRAULIC PUMP
•
The oil in each cylinder of cylinder block (7) can be drawn and discharged through valve plate (8).
Structure • Cylinder block (7) is supported on shaft (1) through spline a. Shaft (1) is supported on the front and rear bearings. • The end of piston (6) is a concave sphere, which holds shoe (5) as a spherical bearing. • Rocker cam (4) has plane A. Shoe (5) is kept pressed against plane A and slid circularly. Rocker cam (4) is supported on flange (2) and ball (12) fixed to the case and slides on the formed static pressure bearing and high-pressure oil. • Piston (6) moves axially and relatively in each cylinder of cylinder block (7). • Cylinder block (7) revolves relatively against valve plate (8), sealing the hydraulic oil. The hydraulic pressure on the revolving surface of the cylinder block is balanced properly.
10-72 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
Operation
HYDRAULIC PUMP
•
1. Operation of pump •
• •
•
Shaft (1) and cylinder block (7) revolve together and shoe (5) slides on plane A. As rocker cam (4) slants around ball (12) at this time, angle ( ) between the center line X of rocker cam (4) and axis of cylinder block (7) changes. Angle ( ) is called the swash plate angle.
• •
If center line X of rocker cam (4) is in the direction of the axis of cylinder block (7) (Swash plate angle = 0), the difference between volumes E and F in cylinder block (7) is 0 and oil is not sucked or discharged (The swash plate angle is not reduced to 0 actually, however). In short, swash plate angle ( ) is in proportion to the discharge of the pump. The number of holes on cylinder block (7) is even 10 and every second one of them is fitted to 2 grooves of valve plate (8). The quantity of the oil equivalent to 5 pistons is discharged to each of P1 and P2.
If the angle between the center line X of rocker cam (4) and the axis of cylinder block (7) is a, plane A works as a cam for shoe (5). Accordingly, piston (6) slides inside cylinder block (7) and makes difference between volumes E and F in cylinder block (7) and the oil is drawn and discharged by the difference. In short, if cylinder block (7) revolves and volume of chamber E is reduced, the oil is discharged. On the other hand, the volume of chamber F is increased and the oil is sucked. (The figure shows the end of suction process of chamber F and the end of discharge process of chamber E.)
PC78US-6
10-73 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
2. Control of discharge
LS valve
•
Function • The LS valve controls the discharge of the pump according to the stroke of the control lever, or the demand flow for the actuator. • The LS valve calculates the demand flow for the actuator fr om differential pr essure PLS between inlet pressure PPLS and outlet pressure PLS of the control valve, and controls discharge Q of the main pump. (PPLS is called the LS pump pressure, PLS the LS pressure, and PLS the LS differential pressure.) • That is, the discharge of the pump is controlled according to the demand flow for the actuator by the following method; The pressure loss made when the oil flows through the opening of the control valve spool (LS differential pressure PLS) is sensed and discharge Q of the pump is so controlled that the pressure loss will be constant. • The LS valve receives main pump discharge pressure PP, LS pump pressure (PPLS), and LS pressure PLS. The relationship between the LS differential pressure ( PLS) and pump discharge Q changes as shown below.
•
If swash plate angle ( ) is increased, the difference between volumes E and F, or discharge Q, is increased. Swash plate angle ( ) is changed with servo piston (11). Servo piston (11) is reciprocated linearly by the signal pressure of PC and LS valves. This linear motion is transmitted to rocker cam (4) supported on flange (2) through ball (12). Then, rocker cam (4) slides in the revolutionary direction.
10-74 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
PC valve Function • The PC valve limits the oil flow to a certain level (according to the discharge pressure) even if the stroke of the control valve is increased so that the horsepower absorbed by the pump will not exceed the engine horsepower, as long as pump discharge pressure PP is high. That is, the PC valve performs constant-horsepower control. • In other words, the PC valve decreases the pump discharge when the load is increased and the pump discharge pressure rises and increases it when the pump discharge pressure lowers. • This pump has 2 discharge openings and the average of discharge pressures P1 and P2 at those openings is sensed. The average of P1 and P2 is called the PAVE. The relationship between this average and pump discharge (discharge from the 2 discharge openings) is shown below.
Operation 1. PC78UU, 78US-6 (With blade) (1) Function of spring • The spring load of spring (2) at the PC valve is decided by the position of the swash plate. • If servo piston (6) moves to the right, spring (2) is compressed through lever (1) and its spring load changes. The spring constant of this spring changes to 2 levels. (2) When pump pressure PAVE is low • The pressure of spool (4) is decreased and spool (3) is a little to the right (Fig. 1 and Fig. 4). At this time, ports C and D are connected to each other and the pressure in the LS valve is drain pressure PT.
PC78US-6
HYDRAULIC PUMP
•
• •
•
At this time, ports F and G of the LS valve are connected to each other. As a result, the pressure in port J becomes drain pressure PT and servo piston (6) moves to the left. Consequently, the pump discharge is increased. As servo piston (6) moves, lever (1) moves to the left and spring (2) expands and its spring load is decreased. Consequently, spool (3) moves to the left to break the connection of ports C and D, and then pump discharge ports B and C are connected. As a result, the pressure in port C rises and the piston pressure is increased and servo piston (6) stops moving to the left.
(3) When pump pressure PAVE is high • The pressure of spool (4) is increased and spool (3) is a little to the left (Fig. 2 and Fig. 5). At this time, ports C and B are connected to each other and the pressure in the LS valve is pump pressure PP. • At this time, ports F and G of the LS valve are connected to each other. As a result, the pressure in port J becomes pump pressure PP and servo piston (6) moves to the right. • Consequently, the pump discharge is decreased. • As servo piston (6) moves, lever (1) moves to the right and spring (2) is compressed and its spring load is increased. Consequently, spool (3) moves to the right to break the connection of ports C and B, and then drain pressure ports D and C are connected. • As a result, the pressure in port C lowers and the piston pressure is decreased and servo piston (6) stops moving to the right. • Accordingly, the stopping position (= pump discharge) of servo piston (6) is decided by the position where the pressure caused by pressure PP applied to spool (4) is balanced with the force of spring (2) applied through spool (3) (Fig. 3 and Fig. 6). (4) When swing gear pump pressure rises/lowers • The pressure of spool (4) changes and the pump discharge changes similarly to the case where the PAVE rises/lowers. • The PC-EPC valve changes the output pressure according to the input current from the controller, then the pressure of spool (5) changes and the pump discharge changes similarly to the case where the PAVE rises/lowers.
10-75 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
When load is light
When load is heavy
10-76 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
When balanced
2. PC78US-6 (Without blade) • Although the swing gear pump is not mounted, the theory of operation of this model is the same as that of the machine equipped with the swing gear pump. When load is light
PC78US-6
10-77 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
HYDRAULIC PUMP
When load is heavy
When balanced
10-78 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
CONTROL VALVE Outline a The control valves of the following types are set. PC78US-6 • • • • • •
Blade-less, without service valve Blade-less, with 1 service valve Blade-less, with 2 service valve With blade, without service valve With blade and 1 service valve With blade and 2 service valve
PC78UU-6 • Without service valve • 1 service valve • 2 service valve a Since each service valve is of add-on type, it can be added or removed later.
1. PC78US-6 blade-less and with 1 service valve (1) Outside view A1: To swing motor A2: To left travel motor A3: To right travel motor A4: To boom cylinder bottom A5: To arm cylinder head A6: To bucket cylinder head A7: To attachment 1 B1: To swing motor B2: To left travel motor B3: To right travel motor B4: To boom cylinder head B5: To arm cylinder bottom B6: To bucket cylinder bottom B7: To attachment 1 BP: From boom RAISE PPC valve LS: To pump LS valve (LS pressure input) P1: From main pump P2: From main pump PP: To pump LS valve (Pump pressure input) PS: From swing holding brake reset solenoid valve
10-80 (10)
PT: To travel pressure switch TB: To tank TC: To oil cooler TS: To tank PA1: From swing right PPC valve PA2: From left travel reverse PPC valve PA3: From right travel reverse PPC valve PA4: From boom raise PPC valve PA5: From arm out PPC valve PA6: From bucket dump PPC valve PA7: From service 1 PPC valve PB1: From swing left PPC valve PB2: From left travel forward PPC valve PB3: From right travel forward PPC valve PB4: From boom lower PPC valve PB5: From arm in PPC valve PB6: From bucket curl PPC valve PB7: From service 1 PPC valve TSW: To swing motor
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(PC78US-6 blade-less and with 1 service valve)
PC78US-6
10-81 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(2) Sectional view Serial No.: 4001 – 6500 (1/4)
(PC78US-6 blade-less and with 1 service valve)
10-82 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Serial No.: 6501 and up (1/4)
(PC78US-6 blade-less and with 1 service valve)
PC78US-6
10-83 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.
Suction valve (Left travel) Suction valve (Right travel) Main relief valve Suction valve (Boom bottom) Suction valve (Arm head) Suction valve (Bucket head) Suction valve (Attachment) Safety valve Suction valve (Attachment) Suction valve (Bucket bottom) Suction valve (Arm bottom) Suction valve (Boom head) Lift check valve Cooler bypass valve Suction valve (Right travel) Suction valve (Left travel) Spool (Swing) Spool (Left travel) Spool (Right travel) Unload valve (P1) Unload valve (P2) Spool (Boom) Spool (Arm) Spool (Bucket) Spool (Attachment) LS pressure pickup plug (LS2) LS pressure pickup plug (LS1) Spool (LS selector)
CONTROL VALVE
29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52.
Pressure compensation valve F (Swing) Pressure compensation valve F (Left travel) Pressure compensation valve F (Right travel) Pressure compensation valve F (Boom) Pressure compensation valve F (Arm) Pressure compensation valve F (Bucket) Pressure compensation valve F (Attachment) Pump pressure pickup plug (P2) LS pressure pickup plug (LS3) Pressure compensation valve R (Attachment) Pressure compensation valve R (Bucket) Pressure compensation valve R (Arm) Pressure compensation valve R (Boom) LS bypass plug (LS2) Logic valve Spool (Pump merge-divider valve) Pressure compensation valve R (Right travel) Pressure compensation valve R (Left travel) Pressure compensation valve R (Swing) Check valve (Attachment) Check valve (Bucket) Check valve (Arm) Boom hydraulic drift prevention valve Check valve (Boom bottom)
F: Flow control valve R: Pressure reducing valve
(PC78US-6 blade-less and with 1 service valve)
10-84 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Unit: mm No.
Item
Criteria Basic dimensions
53
Lift check valve spring
Remedy Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
58.1 X 17.0
36
59.6 N {5.8 kg}
—
47.7 N {4.64 kg}
54
Cooler bypass valve spring
34.5 X 17.7
25
73.5 N {7.5 kg}
—
58.8 N {6.0 kg}
55
Spool return spring (Swing)
29.2 X 17.5
28.5
28.3 N {2.89 kg}
—
22.6 N {2.31 kg}
56
Spool return spring (Travel)
29.0 X 17.5
28.5
22.6 N {2.3 kg}
—
18.1 N {1.84 kg}
57
Spool return spring (Arm in)
41.1 X 19.3
40.5
43.1 N {4.4 kg}
—
34.5 N {3.52 kg}
58
Spool return spring (Work equipment)
41.1 X 19.3
40.5
34.3 N {3.5 kg}
—
27.4 N {2.8 kg}
59
Spool return spring (Arm out)
42.3 X 19.2
40.5
54.9 N {5.6 kg}
—
43.9 N {4.49 kg}
60
Unload valve spring
40.9 X 15.1
33.5
129 N {13.2 kg}
—
103 N {10.6 kg}
61
LS selector valve spring
16.6 X 13.0
13
11.2 N {1.14 kg}
—
8.96 N {0.91 kg}
62
Pressure compensation valve spring
15.4 X 6.0
8
7.45 N {0.76 kg}
—
5.96 N {0.61 kg}
63
Pump merge-divider valve spool return spring
33.2 X 14.2
22.5
49.0 N {5.0 kg}
—
39.2 N {4.0 kg}
64
Pressure compensation valve spring
30.9 X 5.2
20
27.7 N {2.82 kg}
—
22.2 M {2.26 kg}
65
Pressure compensation valve spring
28.0 X 14.4
14.5
13.7 N {1.4 kg}
—
11.0 N {1.12 kg}
66
Pressure compensation valve spring
33.4 X 14.4
21.5
55.9 N {5.7 kg}
—
44.7 N {4.56 kg}
67
Pressure compensation valve spring
20.0 X 8.4
12
6.86 N {0.7 kg}
—
5.49 N {0.56 kg}
68
Pressure compensation valve spring
23.0 X 8.4
15
6.86 N {0.7 kg}
—
5.49 N {0.56 kg}
69
Check valve spring
12.3 X 11.4
10.5
3.92 N {0.4 kg}
—
3.14 N {0.32 kg}
70
Check valve spring
27.2 X 6.9
22
3.92 N {0.4 kg}
—
3.14 N {0.32 kg}
If damaged or deformed, replace spring.
(PC78US-6 blade-less and with 1 service valve)
PC78US-6
10-85 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Serial No.: 4001 – 6500 (2/4)
(PC78US-6 blade-less and with 1 service valve)
10-86 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Serial No.: 6501 and up (2/4)
(PC78US-6 blade-less and with 1 service valve)
PC78US-6
10-87 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.
CONTROL VALVE
Spool (LS selector) Spool (Swing) Pressure compensation valve R (Swing) Pressure compensation valve F (Swing) Pressure compensation valve F (Left travel) Suction valve (Left travel) Spool (Left travel) Suction valve (Left travel) Pressure compensation valve R (Left travel) LS bleed valve Pressure compensation valve F (Right travel) Suction valve (Right travel) Spool (Right travel) Suction valve (Right travel) Pressure compensation valve R (Right travel) Travel junction valve, LS bleed valve Pump pressure pickup plug (P1) Spool (Pump merge-divider valve) Unload valve (P1) Check valve (P1) Cooler bypass valve LS pressure pickup plug (LS1) LS bypass plug (LS1) Logic valve
F: Flow control valve R: Pressure reducing valve
Unit: mm No.
Item
Criteria Basic dimensions
25
Check valve spring
Remedy Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
21.9 X 5.0
15.8
1.96 N {0.2 kg}
—
1.57 N {0.16 kg}
26
Travel junction valve spring
19.3 X 7.5
14
15.7 N {1.6 kg}
—
12.6 N {1.28 kg}
27
Check valve spring
13.0 X 6.5
9
2.26 N {0.23 kg}
—
1.81 N {0.18}
If damaged or deformed, replace spring.
(PC78US-6 blade-less and with 1 service valve)
10-88 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(3/4)
(PC78US-6 blade-less and with 1 service valve)
10-90 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.
CONTROL VALVE
Unload valve (P2) Main relief valve Check valve (P2) Lift check valve LS pressure pickup plug (LS2) LS bypass plug (LS2) Pressure compensation valve F (Boom) Suction valve (Boom bottom) Boom hydraulic drift prevention valve Suction valve (Boom head) Spool (Boom) Pressure compensation valve R (Boom) Suction valve (Arm head) Spool (Arm) Suction valve (Arm bottom) Pressure compensation valve R (Arm) Pressure compensation valve F (Arm) Suction valve (Bucket head) Spool (Bucket) Suction valve (Bucket bottom) Pressure compensation valve R (Bucket) Pressure compensation valve F (Bucket) Suction valve (Attachment) Spool (Attachment) Suction valve (Attachment) Pressure compensation valve R (Attachment) Pressure compensation valve F (Attachment) Pump pressure pickup plug (P2) Safety valve Pressure release plug LS pressure pickup plug (LS3)
F: Flow control valve R: Pressure reducing valve
Unit: mm No.
Item
Criteria Basic dimensions
32
Check valve spring
Remedy Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
13.0 X 6.5
9
2.26 N {0.23 kg}
—
1.81 N {0.18}
33
Hydraulic drift prevention valve spring
16.6 X 13.0
13
11.2 N {1.14 kg}
—
8.96 N {0.91 kg}
34
Hydraulic drift prevention valve spring
13.0 X 8.8
7.7
10.8 N {1.1 kg}
—
8.64 N {0.88 kg}
If damaged or deformed, replace spring.
(PC78US-6 blade-less and with 1 service valve)
PC78US-6
10-91 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(4/4)
(PC78US-6 blade-less and with 1 service valve)
10-92 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4.
CONTROL VALVE
Travel junction valve, LS bleed valve LS bleed valve Check valve (Boom head) Logic valve
Unit: mm No.
Item
Criteria Basic dimensions
5
6
Check valve spring
Logic valve spring
Remedy Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
27.2 X 6.9
22
3.92 N {0.4 kg}
—
3.14 N {0.32 kg}
11.0 X 6.2
9.5
5.5 N {0.56 kg}
—
4.4 N {0.45 kg}
If damaged or deformed, replace spring.
(PC78US-6 blade-less and with 1 service valve)
PC78US-6
10-93 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
2. PC78US-6 with blade and 1 service valve (1) Outside view A1: To blade cylinder head A2: To swing motor A3: To left travel motor A4: To right travel motor A5: To offset cylinder head A6: To boom cylinder bottom A7: To arm cylinder head A8: To bucket cylinder head B1: To blade cylinder bottom B2: To swing motor B3: To left travel motor B4: To right travel motor B5: To offset cylinder bottom B6: To boom cylinder head B7: To arm cylinder bottom B8: To bucket cylinder bottom BP: From boom RAISE PPC valve LS: To pump LS valve (LS pressure input) P1: From main pump P2: From main pump P3: From gear pump PP: To pump LS valve (LS pressure input) PT: To travel pressure switch TB: To tank TC: To oil cooler TS: To tank PA1: From blade raise PPC valve PA2: From swing right PPC valve PA3: From left travel reverse PPC valve PA4: From right travel reverse PPC valve PA5: From offset right PPC valve PA6: From boom raise PPC valve PA7: From arm out PPC valve PA8: From bucket dump PPC valve PB1: From blade lower PPC valve PB2: From swing left PPC valve PB3: From left travel forward PPC valve PB4: From right travel forward PPC valve PB5: From offset left PPC valve PB6: From boom lower PPC valve PB7: From arm in PPC valve PB8: From bucket curl PPC valve TSW: To swing motor
10-94 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(PC78US-6 with blade and 1 service valve)
PC78US-6
10-95 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(2) Sectional view Serial No.: 4001 – 6500 (1/4)
(PC78US-6 with blade and 1 service valve)
10-96 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Serial No.: 6501 and up (1/4)
(PC78US-6 with blade and 1 service valve)
PC78US-6
10-97 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30.
Safety-suction valve (Blade head) Suction valve (Left travel) Suction valve (Right travel) Main relief valve Suction valve (Boom bottom) Suction valve (Arm head) Suction valve (Bucket head) Suction valve (Attachment) Safety valve Suction valve (Attachment) Suction valve (Bucket bottom) Suction valve (Arm bottom) Suction valve (Boom head) Cooler bypass valve Suction valve (Right travel) Suction valve (Left travel) Suction valve (Blade bottom) Gear pump relief valve Spool (Boom raise merge) Spool (Blade) Spool (Swing) Spool (Left travel) Spool (Right travel) Unload valve (P1) Unload valve (P2) Spool (Boom) Spool (Arm) Spool (Bucket) Spool (Attachment) LS pressure pickup plug (LS2)
CONTROL VALVE
31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57.
LS pressure pickup plug (LS1) Pressure compensation valve F (Left travel) Pressure compensation valve F (Right travel) Pressure compensation valve F (Boom) Pressure compensation valve F (Arm) Pressure compensation valve F (Bucket) Pressure compensation valve F (Attachment) Pump pressure pickup plug (P2) LS pressure pickup plug (LS3) Pressure compensation valve R (Attachment) Pressure compensation valve R (Bucket) Pressure compensation valve R (Arm) Pressure compensation valve R (Boom) LS bypass plug (LS2) Logic valve Spool (Pump merge-divider valve) Pressure compensation valve R (Right travel) Pressure compensation valve R (Left travel) Check valve (Swing) LS bleed valve Travel junction valve, LS bleed valve Check valve (Attachment) Check valve (Bucket) Check valve (Arm) Boom hydraulic drift prevention valve Check valve (Boom bottom) Check valve (Blade)
F: Flow control valve R: Pressure reducing valve
(PC78US-6 with blade and 1 service valve)
10-98 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Unit: mm No.
Item
Criteria
Remedy
Basic dimensions 58
Cooler bypass valve spring
Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
34.5 X 17.7
25
73.5 N {7.5 kg}
—
58.8 N {6.0 kg}
59
Spool return spring (Blade, swing)
29.0 X 18.3
27.5
89.5 N {9.1 kg}
—
71.6 N {7.28 kg}
60
Spool return spring (Travel)
29.0 X 17.5
28.5
22.6 N {2.3 kg}
—
18.1 N {1.84 kg}
61
Spool return spring (Arm in)
41.1 X 19.3
40.5
43.1 N {4.4 kg}
—
34.5 N {3.52 kg}
62
Spool return spring (Work equipment)
41.1 X 19.3
40.5
34.3 N {3.5 kg}
—
27.4 N {2.8 kg}
63
Spool return spring (Arm out)
42.3 X 19.2
40.5
54.9 N {5.6 kg}
—
43.9 N {4.49 kg}
64
Unload valve spring
40.9 X 15.1
33.5
129 N {13.2 kg}
—
103 N {10.6 kg}
65
Boom RAISE merge valve spring
16.6 X 13.0
13
11.2 N {1.14 kg}
—
8.96 N {0.91 kg}
66
Pump merge-divider valve spool return spring
33.2 X 14.2
22.5
49.0 N {5.0 kg}
—
39.2 N {4.0 kg}
67
Pressure compensation valve spring
30.9 X 5.2
20
27.7 N {2.82 kg}
—
22.2 M {2.26 kg}
68
Pressure compensation valve spring
28.0 X 14.4
14.5
13.7 N {1.4 kg}
—
11.0 N {1.12 kg}
69
Pressure compensation valve spring
33.4 X 14.4
21.5
55.9 N {5.7 kg}
—
44.7 N {4.56 kg}
70
Pressure compensation valve spring
20.0 X 8.4
12
6.86 N {0.7 kg}
—
5.49 N {0.56 kg}
71
Check valve spring
13.0 X 6.5
9
2.26 N {0.23 kg}
—
1.81 N {0.18}
72
Check valve spring
27.2 X 6.9
22
3.92 N {0.4 kg}
—
3.14 N {0.32 kg}
73
Check valve spring
12.3 X 11.4
10.5
3.92 N {0.4 kg}
—
3.14 N {0.32 kg}
74
Check valve spring
21.9 X 5.0
15.8
1.96 N {0.2 kg}
—
1.57 N {0.16 kg}
75
Spool return spring (Boom)
41.13 X 19.3
38.5
136.41 N {13.91 kg}
—
109 N {11.1 kg}
76
Spool return spring (Blade)
29.01 X 18.3
27.5
89.5 N {9.1 kg}
—
71.6 N {7.3 kg}
If damaged or deformed, replace spring.
(PC78US-6 with blade and 1 service valve)
PC78US-6
10-99 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Serial No.: 4001 – 6500 (2/4)
(PC78US-6 with blade and 1 service valve)
10-100 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Serial No.: 6501 and up (2/4)
(PC78US-6 with blade and 1 service valve)
PC78US-6
10-101 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.
CONTROL VALVE
Spool (Boom raise merge) Gear pump relief valve Safety-suction valve (Blade head) Suction valve (Blade bottom) Spool (Blade) Check valve (Blade) Spool (Swing) Check valve (Swing) Pressure compensation valve F (Left travel) Suction valve (Left travel) Spool (Left travel) Suction valve (Left travel) Pressure compensation valve R (Left travel) LS bleed valve Pressure compensation valve F (Right travel) Suction valve (Right travel) Spool (Right travel) Suction valve (Right travel) Pressure compensation valve R (Right travel) Travel junction valve, LS bleed valve Pump pressure pickup plug (P1) Unload valve (P1) Check valve (P1) Cooler bypass valve LS pressure pickup plug (LS1) LS bypass plug (LS1) Logic valve Spool (Pump merge-divider valve)
F: Flow control valve R: Pressure reducing valve
Unit: mm No.
Item
Criteria
Remedy
Basic dimensions 29
Check valve spring
Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
21.9 X 5.0
15.8
1.96 N {0.2 kg}
—
1.57 N {0.16 kg}
30
Travel junction valve spring
19.3 X 7.5
14
15.7 N {1.6 kg}
—
12.6 N {1.28 kg}
31
Check valve spring
13.0 X 6.5
9
2.26 N {0.23 kg}
—
1.81 N {0.18}
If damaged or deformed, replace spring.
(PC78US-6 with blade and 1 service valve)
10-102 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(3/4)
(PC78US-6 with blade and 1 service valve)
10-104 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.
CONTROL VALVE
Logic valve Unload valve (P2) Main relief valve Check valve (P2) LS pressure pickup plug (LS2) LS bypass plug (LS2) Suction valve (Boom bottom) Boom hydraulic drift prevention valve Suction valve (Boom head) Spool (Boom) Pressure compensation valve R (Boom) Pressure compensation valve F (Boom) Suction valve (Arm head) Spool (Arm) Suction valve (Arm bottom) Pressure compensation valve R (Arm) Pressure compensation valve F (Arm) Suction valve (Bucket head) Spool (Bucket) Suction valve (Bucket bottom) Pressure compensation valve R (Bucket) Pressure compensation valve F (Bucket) Suction valve (Attachment) Spool (Attachment) Suction valve (Attachment) Pressure compensation valve R (Attachment) Pressure compensation valve F (Attachment)
F: Flow control valve R: Pressure reducing valve
Unit: mm No.
Item
Criteria
Remedy
Basic dimensions 28
Check valve spring
Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
13.0 X 6.5
9
2.26 N {0.23 kg}
—
1.81 N {0.18}
29
Hydraulic drift prevention valve spring
16.6 X 13.0
13
11.2 N {1.14 kg}
—
8.96 N {0.91 kg}
30
Hydraulic drift prevention valve spring
13.0 X 8.8
7.7
10.8 N {1.1 kg}
—
8.64 N {0.88 kg}
If damaged or deformed, replace spring.
(PC78US-6 with blade and 1 service valve)
PC78US-6
10-105 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(4/4)
(PC78US-6 with blade and 1 service valve)
10-106 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9.
CONTROL VALVE
Pump pressure pickup plug (P2) Safety valve Pressure release plug LS pressure pickup plug (LS3) LS bleed valve Travel junction valve, LS bleed valve Check valve (Boom head) Boom hydraulic drift prevention valve Logic valve
Unit: mm No.
Item
Criteria
Remedy
Basic dimensions 10
11
Check valve spring
Logic valve spring
Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
27.2 X 6.9
22
3.92 N {0.4 kg}
—
3.14 N {0.32 kg}
11.0 X 6.2
9.5
5.5 N {0.56 kg}
—
4.4 N {0.45 kg}
If damaged or deformed, replace spring.
(PC78US-6 with blade and 1 service valve)
PC78US-6
10-107 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
3. PC78UU-6 without service valve (1) Outside view A1: To blade cylinder head A2: To swing motor A3: To left travel motor A4: To right travel motor A5: To offset cylinder head A6: To boom cylinder bottom A7: To arm cylinder head A8: To bucket cylinder head B1: To blade cylinder bottom B2: To swing motor B3: To left travel motor B4: To right travel motor B5: To offset cylinder bottom B6: To boom cylinder head B7: To arm cylinder bottom B8: To bucket cylinder bottom BP: From boom RAISE PPC valve LS: To pump LS valve (LS pressure input) P1: From main pump P2: From main pump P3: From gear pump PP: To pump LS valve (Pump pressure input) PT: To travel pressure switch TB: To tank TC: To oil cooler TS: To tank PA1: From blade raise PPC valve PA2: From swing right PPC valve PA3: From left travel reverse PPC valve PA4: From right travel reverse PPC valve PA5: From offset right PPC valve PA6: From boom raise PPC valve PA7: From arm out PPC valve PA8: From bucket dump PPC valve PB1: From blade lower PPC valve PB2: From swing left PPC valve PB3: From left travel forward PPC valve PB4: From right travel forward PPC valve PB5: From offset left PPC valve PB6: From boom lower PPC valve PB7: From arm in PPC valve PB8: From bucket curl PPC valve TSW: To swing motor
10-108 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(PC78UU-6 without service valve)
PC78US-6
10-109 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(2) Sectional view (1/4)
(PC78UU-6 without service valve)
10-110 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.
Safety-suction valve (Blade head) Suction valve (Left travel) Suction valve (Right travel) Suction valve (Offset head) Main relief valve Suction valve (Boom bottom) Suction valve (Arm head) Suction valve (Bucket head) Safety valve Suction valve (Bucket bottom) Suction valve (Arm bottom) Suction valve (Boom head) Cooler bypass valve Suction valve (Right travel) Suction valve (Left travel) Suction valve (Blade bottom) Gear pump relief valve Spool (Boom raise merge) Spool (Blade) Spool (Swing) Spool (Left travel) Spool (Right travel) Spool (Offset) Unload valve (P1) Unload valve (P2) Spool (Boom) Spool (Arm) Spool (Bucket) LS pressure pickup plug (LS2)
CONTROL VALVE
30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54.
LS pressure pickup plug (LS1) Pressure compensation valve F (Left travel) Pressure compensation valve F (Right travel) Pressure compensation valve F (Offset) Pressure compensation valve F (Boom) Pressure compensation valve F (Arm) Pressure compensation valve F (Bucket) Pump pressure pickup plug (P2) LS pressure pickup plug (LS3) Pressure compensation valve R (Bucket) Pressure compensation valve R (Arm) Pressure compensation valve R (Boom) LS bypass plug (LS2) Logic valve Spool (Pump merge-divider valve) Pressure compensation valve R (Offset) Pressure compensation valve R (Right travel) Pressure compensation valve R (Left travel) Check valve (Blade) Check valve (Swing) LS bleed valve Travel junction valve, LS bleed valve Check valve (Bucket) Check valve (Arm) Check valve (Boom bottom)
F: Flow control valve R: Pressure reducing valve
(PC78UU-6 without service valve)
PC78US-6
10-111 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
Unit: mm No.
Item
Criteria Basic dimensions
55
Cooler bypass valve spring
Remedy Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
34.5 X 17.7
25
73.5 N {7.5 kg}
–
58.8 N {6.0 kg}
56
Spool return spring (Blade, swing)
29.0 X 18.3
27.5
89.5 N {9.1 kg}
–
71.6 N {7.28 kg}
57
Spool return spring (Travel, offset)
29.0 X 17.5
28.5
22.6 N {2.3 kg}
–
18.1 N {1.84 kg}
58
Spool return spring (Work equipment)
41.1 X 19.3
40.5
34.3 N {3.5 kg}
–
27.4 N {2.8 kg}
59
Spool return spring (Arm out)
42.3 X 19.2
40.5
54.9 N {5.6 kg}
–
43.9 N {4.48 kg}
60
Unload valve spring
40.9 X 15.1
33.5
129 N {13.2 kg}
–
103 N {10.6 kg}
61
Boom RAISE merge valve spring
16.6 X 13.0
13
11.2 N {1.14 kg}
–
8.96 N {0.91 kg}
62
Pump merge-divider valve spool return spring
33.2 X 14.2
22.5
49.0 N {5.0 kg}
–
39.2 N {4.0 kg}
63
Pressure compensation valve spring
30.9 X 5.2
20
27.7 N {2.82 kg}
–
22.2 M {2.26 kg}
64
Pressure compensation valve spring
28.0 X 14.4
14.5
13.7 N {1.4 kg}
–
11.0 N {1.12 kg}
65
Pressure compensation valve spring
33.4 X 14.4
21.5
55.9 N {5.7 kg}
–
44.7 N {4.56 kg}
66
Pressure compensation valve spring
20.0 X 8.4
12
6.86 N {0.7 kg}
–
5.49 N {0.56 kg}
67
Check valve spring
13.0 X 6.5
9
2.26 N {0.23 kg}
–
1.81 N {0.18}
68
Check valve spring
27.2 X 6.9
22
3.92 N {0.4 kg}
–
3.14 N {0.32 kg}
69
Check valve spring
12.3 X 11.4
10.5
3.92 N {0.4 kg}
–
3.14 N {0.32 kg}
70
Check valve spring
21.9 X 5.0
15.8
1.96 N {0.2 kg}
–
1.57 N {0.16 kg}
If damaged or deformed, replace spring.
(PC78UU-6 without service valve)
10-112 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(2/4)
(PC78UU-6 without service valve)
10-114 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.
CONTROL VALVE
Spool (Boom raise merge) Gear pump relief valve Safety-suction valve (Blade head) Suction valve (Blade bottom) Spool (Blade) Check valve (Blade) Spool (Swing) Check valve (Swing) Suction valve (Left travel) Spool (Left travel) Suction valve (Left travel) Pressure compensation valve R (Left travel) LS bleed valve Pressure compensation valve F (Left travel) Suction valve (Right travel) Spool (Right travel) Suction valve (Right travel) Pressure compensation valve R (Right travel) Travel junction valve, LS bleed valve Pressure compensation valve F (Right travel) Suction valve (Offset head) Spool (Offset) Pressure compensation valve R (Offset) Pressure compensation valve F (Offset)
F: Flow control valve R: Pressure reducing valve
Unit: mm No.
Item
Criteria Basic dimensions
25
26
Check valve spring
Travel junction valve spring
Remedy Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
21.9 X 5.0
15.8
1.96 N {0.2 kg}
—
1.57 N {0.16 kg}
19.3 X 7.5
14
15.7 N {1.6 kg}
—
12.6 N {1.28 kg}
If damaged or deformed, replace spring.
(PC78UU-6 without service valve)
PC78US-6
10-115 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(3/4)
(PC78UU-6 without service valve)
10-116 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.
CONTROL VALVE
Unload valve (P1) Check valve (P1) LS pressure pickup plug (LS1) Cooler bypass valve Logic valve LS bypass plug (LS1) Spool (Pump merge-divider valve) Pump pressure pickup plug (P1) Main relief valve Check valve (P2) LS pressure pickup plug (LS2) LS bypass plug (LS2) Unload valve (P2) Suction valve (Boom bottom) Boom hydraulic drift prevention valve Suction valve (Boom head) Spool (Boom) Pressure compensation valve R (Boom) Pressure compensation valve F (Boom) Suction valve (Arm head) Spool (Arm) Suction valve (Arm bottom) Pressure compensation valve R (Arm) Pressure compensation valve F (Arm) Suction valve (Bucket head) Spool (Bucket) Suction valve (Bucket bottom) Pressure compensation valve R (Bucket) Pressure compensation valve F (Bucket)
F: Flow control valve R: Pressure reducing valve
Unit: mm No.
Item
Criteria Basic dimensions
30
Check valve spring
Remedy Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
13.0 X 6.5
9
2.26 N {0.23 kg}
—
1.81 N {0.18}
31
Hydraulic drift prevention valve spring
16.6 X 13.0
13
11.2 N {1.14 kg}
—
8.96 N {0.91 kg}
32
Hydraulic drift prevention valve spring
13.0 X 8.8
7.7
10.8 N {1.1 kg}
—
8.64 N {0.88 kg}
If damaged or deformed, replace spring.
(PC78UU-6 without service valve)
PC78US-6
10-117 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CONTROL VALVE
(4/4)
(PC78UU-6 without service valve)
10-118 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
1. 2. 3. 4. 5. 6. 7. 8. 9.
CONTROL VALVE
Safety valve Pressure release plug LS pressure pickup plug (LS3) Pump pressure pickup plug (P2) LS bleed valve Travel junction valve, LS bleed valve Boom hydraulic drift prevention valve Check valve (Boom head) Logic valve
F: Flow control valve R: Pressure reducing valve Unit: mm No.
Item
Criteria Basic dimensions
10
11
Check valve spring
Logic valve spring
Remedy Allowable limit
Free length x Outside diameter
Installed length
Installed load
Free length
Installed load
27.2 X 6.9
22
3.92 N {0.4 kg}
—
3.14 N {0.32 kg}
11.0 X 6.2
9.5
5.5 N {0.56 kg}
—
4.4 N {0.45 kg}
If damaged or deformed, replace spring.
(PC78UU-6 without service valve)
PC78US-6
10-119 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
CLSS OUTLINE OF CLSS Features CLSS stands for Closed center Load Sensing System, and has the following featues. • Fine control not influenced by load • Control enabling digging even with fine control • Ease of compound operation ensured by flow divider function using area of opening of spoll during compund operations • Energy saving using variable pump control
10-120 (10)
Structure • The CLSS consists of a variable capacity single piston pump, control valve, and actuators. • The pump body consists of the main pump, PC valve and LS valve.
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
BASIC PRINCIPLE 1. Control of pump swash plate angle • The pump swash plate angle (pump discharge amount) is controlled so that LS differential pressure PLS (the difference between pump (discharge) pressure PP and control valve outlet port LS pressure PLS) load pressure of actuator) is constant. (LS pressure PLS=Pump discharge pressure PP–LS pressure PLS)
•
If LS differential pressure PLS becomes lower than the set pressure of the LS valve (when the actuator load pressure is high), the pump swash plate moves towards the maximum position; if the set pressure becomes higher than the set pressure of the LS valve (when the actuator load pressure is low), the pump swash plate moves towards the minimum position. a For details of the operation, see HYDRAULIC PUMP.
PC78US-6
10-121 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
2. Pressure compensation control • A pressure compensation valve is installed to the inlet port side of the control valve spool to balance the load. When to actuators are operated together, this valve acts to make pressure difference P
10-122 (10)
CLSS
between the upstream (inlet port) and downstream (outlet port) the same, regardless of the size of the load (pressure). In this way, the flow of oil from the pump is divided (compensated) in proportion to the area of openings S1 and S2 of each valve when it is operated.
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
OPERATION FOR EACH FUNCTION AND VALVE Hydraulic circuit diagram and name of valves (PC78US-6 Blade-less, 1 service valve)
10-124 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
1. Unload valve (P1) Set pressure: LS pressure + 2.45 MPa {25 kg/cm2} 2. Unload valve (P2) Set pressure: LS pressure + 2.45 MPa {25 kg/cm2} 3. Main relief valve Set pressure: 26.5 MPa {270 kg/cm2} 4. Lift check valve 5. Cooler bypass valve 6. Suction valve 7. Safety valve Set pressure: 27.9 MPa {285 kg/cm2} 8. Pressure compensation valve 9. LS bypass plug (P1) 10. LS bypass plug (P2) 11. LS selector valve 12. LS bleed valve 13. Travel junction valve, LS bleed valve 14. Logic valve 15. Boom hydraulic drift prevention valve
PC78US-6
10-125 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
(PC78US-6 with blade and 1 service valve)
10-126 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
1. Unload valve (P1) Set pressure: LS pressure + 2.45 MPa {25 kg/cm2} 2. Unload valve (P2) Set pressure: LS pressure + 2.45 MPa {25 kg/cm2} 3. Main relief valve Set pressure: 26.5 MPa {270 kg/cm2} 4. Gear pump relief valve Set pressure: 21.1 MPa {215 kg/cm2} 5. Cooler bypass valve 6. Suction valve 7. Safety-suction valve Set pressure: 9.8 MPa {100 kg/cm2} 8. Safety valve Set pressure: 27.9 MPa {285 kg/cm2} 9. Pressure compensation valve 10. LS bypass plug (P1) 11. LS bypass plug (P2) 12. Boom raise merge valve 13. LS bleed valve 14. Travel junction valve, LS bleed valve 15. Logic valve 16. Boom hydraulic drift prevention valve
PC78US-6
10-127 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
(PC78US-6 without service valve)
10-128 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
1. Unload valve (P1) Set pressure: LS pressure + 2.45 MPa {25 kg/cm2} 2. Unload valve (P2) Set pressure: LS pressure + 2.45 MPa {25 kg/cm2} 3. Main relief valve Set pressure: 26.5 MPa {270 kg/cm2} 4. Gear pump relief valve Set pressure: 21.1 MPa {215 kg/cm2} 5. Cooler bypass valve 6. Suction valve 7. Safety-suction valve Set pressure: 9.8 MPa {100 kg/cm2} 8. Safety valve Set pressure: 27.9 MPa {285 kg/cm2} 9. Pressure compensation valve 10. LS bypass plug (P1) 11. LS bypass plug (P2) 12. Boom raise merge valve 13. LS bleed valve 14. Travel junction valve, LS bleed valve 15. Logic valve 16. Boom hydraulic drift prevention valve (PC78UU-6 without service valve)
PC78US-6
10-129 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Unload valve 1. When control valve is at HOLD
Function • When the control valve is at HOLD, pump discharge amount Q discharged by the minimum swash plate angle is released to the tank circuit. At this time, pump discharge pressure PP1/PP2 is set at 2.45 MPa {25.0 kg/cm2} by spring (2) in the valve. (LS pressure PLS1/PLS2: 0 MPa {0 kg/cm2}) • Since the pump merge-divider valve is at the merge position, pump discharge pressures PP1 and PP2 are merged. LS pressures PLS1, PLS2, and PLS3 are also merged.
•
•
•
When the control valve is at HOLD, LS pressures PLS1 and PLS2 are not generated, so only pump discharge pressures PP1 and PP2 act, and PP1 and PP2 are set by only the load of spring (2). As pump discharge pressure PP1/PP2 rises and reaches the load of spring (2) (2.45 MPa {25.0 kg/cm2}), spool (1) is moved to the right. Pump discharge pressures PP1 and PP2 are connected to tank circuit T through the cut of spool (1) As a result, pump discharge pressure PP1/PP2 is set to 2.45 MPa {25.0 kg/cm2}.
Operation • Pump discharge pressures PP1 and PP2 are acting on the left end of unload spool (1) and LS pressures PLS1 and PLS2 are acting on the right end. (PP1 = PP2, PLS1 = PLS2)
10-130 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
2. During fine control of work equipment valve Work equipment valve: Swing (PC78US-6 without blade), boom, arm, bucket, or attachment.
Function • During fine control of the work equipment valve, when the demand flow for the actuator is within the amount discharged by the minimum swash plate angle of the pump, pump discharge pressure PP1/PP2 is set to LS pressure PLS1/PLS2 + 2.45 MPa {25.0 kg/cm2}. When the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 reaches the load of spring (2) (2.45 MPa {25.0 kg/cm 2 }), unload spool (1) opens, so LS differential pressure PLS becomes 2.45 MPa {25 kg/cm2}. • Since the pump merge-divider valve is at the merge position, pump discharge pressures PP1 and PP2 are merged. LS pressures PLS1, PLS2, and PLS3 are also merged.
PC78US-6
Operation • When fine control is carried out on the work equipment valve, LS pressures PLS1 and PLS2 are generated and act on the right end of spool (1) (PP1 = PP2, PLS1 = PLS2). When this happens, the area of the opening of the work equipment valve spool is small, so LS pressures PLS1 and PLS2 are very different from pump discharge pressures PP1 and PP2. • When the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 reaches the load of spring (2) (2.45 MPa {25.0 kg/cm2}), spool (1) moves to the right, and pump discharge pressures PP1 and PP2 are connected to tank circuit T. • In other words, pump discharge pressure PP1/ PP2 is set to the spring force (2.45 MPa {25.0 kg/cm2}) + LS pressure PLS1/PLS2, and LS differential pressure PLS becomes 2.45 MPa {25.0 kg/cm2}.
10-131 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
3. When work equipment valve is operated Work equipment valve: Swing (PC78US-6 without blade), boom, arm, bucket, or attachment
Function • When any work equipment valve is operated if the demand flow for the actuator becomes greater than the pump discharge from the minimum swash plate angle, the oil flow to tank circuit T is cut off, and all pump discharge amount Q flows to the actuator circuit. • Since the pump merge-divider valve is at the merge position, pump discharge pressures PP1 and PP2 are merged. LS pressures PLS1, PLS2, and PLS3 are also merged.
•
•
For this reason, the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 does not reach the load of spring (2) (2.45 MPa {25.0 kg/cm2}), so spool (1) is pushed to the left by spring (2). As a result, pump discharge pressures PP1 and PP2 and tank circuit T are shut off, and all pump discharge amount Q flows to the actuator circuit.
Operation • When any work equipment valve is operated for a long stroke, LS pressures PLS1 and PLS2 are generated and act on the right end of unload spool (1) (PP1 = PP2, PLS1 = PLS2). When this happens, the area of the opening of the work equipment valve spool is large, so LS pressures PLS1 and PLS2 are not so different from pump discharge pressures PP1 and PP2.
10-132 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
4. During fine control of both travel valves
Function • During fine control of both travel valves, when the demand flow is below the maximum pump discharge amount, pump discharge pressure PP1/PP2 is set to LS pressure PLS1/PLS2 + 2.45 MPa {25.0 kg/cm2}. • When the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 reaches the load of spring (2) (2.45 MPa {25.0 kg/cm2}), unload spool (1) opens, so excessive oil (maximum pump discharge mount – demand flow) flows into the tank circuit. • Since the pump merge-divider valve is at the separate position, pump discharge pressures PP1 and PP2 are separated. LS pressures PLS1 and PLS2 are also separated. • The swash plate angle of the pump becomes maximum, so the pump discharge amount becomes maximum. (For details, see the sections on the pump merge-divider valve and logic valve.)
PC78US-6
Operation • When fine control is carried out on both travel valves, LS pressures PLS1 and PLS2 are generated and act on the right end of spool (1) (PP1, PP2, PLS1, and PLS2 are separated). • When this happens, the area of the opening of both travel valve spools is small, so LS pressures PLS1 and PLS2 are very different from pump discharge pressures PP1 and PP2. • When the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 reaches the load of spring (2) (2.45 MPa {25.0 kg/cm2}), spool (1) moves to the right, and pump discharge pressures PP1 and PP2 are connected to tank circuit T and the excessive oil (maximum pump discharge mount – demand flow) flows. • In other words, the excessive oil (maximum pump discharge mount – demand flow) above the strokes of both travel valves flows into tank circuit T.
10-133 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
5. When both travel valves are operated
Function • During operation of both travel valves, when the demand flow becomes maximum, the oil flow to tank circuit T is cut off, and all pump discharge amount Q flows to both travel circuits. • Since the pump merge-divider valve is at the separate position, pump discharge pressures PP1 and PP2 are separated. LS pressures PLS1 and PLS2 are also separated. • The swash plate angle of the pump becomes maximum, so the pump discharge amount becomes maximum. (For details, see the sections on the pump merge-divider valve and logic valve.)
•
•
•
When this happens, the area of the openings of both travel valve spools is large, so LS pressures PLS1 and PLS2 are not so different from pump discharge pressures PP1 and PP2. For this reason, the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 does not reach the load of spring (2) (2.45 MPa {25.0 kg/cm2}), so spool (1) is pushed to the left by spring (2). As a result, pump discharge pressures PP1 and PP2 and tank circuit T are shut off, and all pump discharge amount Q flows to the actuator circuit.
Operation • When both travel valves are operated to the stroke ends, LS pressures PLS1 and PLS2 are generated and act on the right end of unload spool (1) (PP1, PP2, PLS1, and PLS2 are separated).
10-134 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
6. When either travel valve is operated
Function • The demand flow decided by the valve stroke is sent to the travel circuit on the operated travel valve side and the all pump discharge amount is sent to the tank circuit on the non-operated travel valve side. • Since the pump merge-divider valve is at the separate position, pump discharge pressures PP1 and PP2 are separated. LS pressures PLS1 and PLS2 are also separated. • The swash plate angle of the pump becomes maximum, so the pump discharge amount becomes maximum. (For details, see the sections on the pump merge-divider valve and logic valve.)
•
Operation When left travel valve is operated to stroke end and right one is at HOLD. • When the left travel valve is operated to the stroke end, LS pressure PLS1 is generated and acts on the right end of unload spool (1).
•
PC78US-6
•
•
•
When this happens, the area of the openings of both travel valve spools is large, so LS pressures PLS1 is not so different from pump discharge pressures PP1. For this reason, the difference between pump discharge pressure PP1 and LS pressure PLS1 does not reach the load of spring (2) (2.45 MPa {25.0 kg/cm2}), so spool (1) is pushed to the left by spring (2). As a result, pump discharge pressures PP1 and tank circuit T are shut off, and all pump discharge amount QP1 on the P1 side flows to the left travel circuit. Since the right travel valve is at HOLD, LS pressure PLS2 is not generated, so only pump discharge pressure PP2 acts. When pump discharge pressure PP2 reaches the load of spring (4) (2.45 MPa {25.0 kg cm2}), spool (3) moves to the right, and all pump discharge amount QP2 on the P2 side flows into tank circuit T.
10-135 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Pump merge-divider valve and logic valve 1. When control valve is at HOLD
Function • Pump merge-divider valve spool (3) merges pump discharge pressures PP1 and PP2 and LS pressures PLS1, PLS2, and PLS3 respectively. Operation • When the control valve is at HOLD, changeover pressure is not generated on logic spool (1), so spring (2) pushes spool (1) to the left. • Since both travel valves are at HOLD, changeover pressure is not generated on the pump mergedivider spool. • When the control valve is at HOLD, changeover pressure is not generated on the pump mergedivider spool, so spring (4) pushes spool (3) to the right. • Pump discharge pressures PP1 and PP2 and LS pressures PLS1, PLS2, and PLS3 are merged respectively (PP1 = PP2, PLS1 = PLS2 = PLS3).
10-136 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
2. When work equipment valve is operated (including compound operation of work equipment + travel). Work equipment valve: Swing (PC78US-6 without blade), boom, arm, bucket, or attachment.
Function • Pump merge-divider valve spool (3) merges pump discharge pressures PP1 and PP2 and LS pressures PLS1, PLS2, and PLS3 respectively. • As the LS pressure, PLS1, PLS2, and PLS3 are output.
• •
When the work equipment valve is operated, changeover pressure for spool (3) is not generated, so spring (4) pushes spool (3) to the right. Pump discharge pressures PP1 and PP2 are merged. LS pressures PLS1, PLS2, and PLS3 are also merged (PP1 = PP2, PLS1 = PLS2 = PLS3).
Operation • When any work equipment valve is operated, the work equipment PPC pressure or the swing holding brake release pressure is introduced in the left chamber of logic spool (1) to change over spool (1). • When the load of spring (2) reaches 0.6 MPa {6 kg/cm2}, spool (1) moves to the right. • As a result, the right chamber of spool (3) is connected to tank circuit T and changeover pressure for spool (3) is not generated.
PC78US-6
10-137 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
3. When either or both travel valves are operated
Function • Pump merge-divider valve spool (3) separates pump discharge pressures PP1 and PP2 and LS pressures PLS1, PLS2, and PLS3 respectively. • As the LS pressure, higher pressure of PP1 and PP2 is output. Operation • Since the all work equipment valves are at HOLD, changeover pressure for logic spool (1) is not generated, spring (2) pushes spool (1) to the left. • When both travel valves are operated, travel PPC pressure is introduced as changeover pressure for spool (3) through spool (1) into the right chamber of spool (3). • When the load of spring (4) reaches 0.49 MPa {5 kg/cm2}, spool (3) is pushed to the left. • As a result, pump discharge pressures PP1 and PP2 and LS pressures PLS1 and PLS2 are separated respectively.
10-138 (10)
• •
Furthermore, PP1 and PLS1 are separated for the left travel circuit and PP2 and PLS2 are separated for the right travel circuit. The higher pressure of pump discharge pressures PP1 and PP2 is output as the LS pressure and the swash plate angle of the pump becomes maximum, so the pump discharge amount becomes maximum.
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Introduction of LS pressure 1. Work equipment valve: Swing (PC78US-6 without blade), boom, arm, bucket, or attachment
Function • The LS pressure is the actuator load pressure at the outlet port end of the control valve. • Actually, pump discharge pressure PP is reduced by reducing valve (3) of the pressure compensation valve to the same pressure as actuator circuit pressure A and sent to LS circuit PLS. • In the travel valve, actuator circuit pressure A is directly introduced to LS circuit PLS. Operation • When spool (1) is operated, pump discharge pressure PP flows from flow control valve (2) through notch (a) in the spool and bridge passage (b) to actuator circuit A. • At the same time, reducing valve (3) also moves to the right, so pump discharge pressure PP is reduced by the pressure loss at notch (c). It goes to LS circuit PLS, and then goes to spring chamber PLSS.
PC78US-6
• •
•
When this happens, LS circuit PLS is connected to tank circuit T from LS bypass plug (4) (See the section on the LS bypass plug). The areas at both ends of reducing valve (3) are the same (SA = SLS), and actuator circuit pressure PA acts on the SA end. The reduced pump discharge pressure PP acts on SLS at the other end. As a result, reducing valve (3) is balanced at a position where actuator circuit pressure PA and the pressure of spring chamber PLSS are the same. Pump discharge pressure PP reduced at notch (c) becomes actuator pressure A and is introduced into LS circuit PLS.
10-139 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
2. Travel valve
Operation • When spool (1) is operated, pump discharge pressure PP flows from flow control valve (2) through notch (a) in the spool and bridge passage (b) to actuator circuit A. • At the same time, reducing valve (3) is moved to the right by actuator circuit pressure PA, and notch (c) and notch (d) are interconnected respectively with travel junction circuit (e) and LS circuit PLS. • As a result, actuator circuit pressure PA (= A) is introduced from notch (c) through the internal check valve and notch (d) into LS circuit PLS. a The travel circuit is different from the work equipment circuit: actuator circuit pressure PA is directly introduced into LS circuit PLS.
10-140 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
LS bypass plug When work equipment valve is operated
When both travel valves are operated
Function • The LS bypass plug releases the residual pressure of LS pressure PLS. • This lowers the rising speed of LS pressure PLS. In addition, the discarded throttled flow causes a pressure loss in the throttled flow in the reducing valve, and that lowers the effective LS differential pressure to improve the stability. Operation 1. When work equipment valve is operated (including compound operation of work equipment + travel) • Since pump merge-divider spool (1) is at the merge position, the hydraulic oil in LS circuits PC78US-6
PLS1, PLS2, and PLS3 flows from tip filter (a) of LS bypass plug (2) through orifice (b) to tank circuit T. 2. When either or both travel valves are operated • Since pump merge-divider spool (1) is at the separate position, LS circuits PLS1, PLS2, and PLS3 are separated. • The hydraulic oil PLS1 flows from tip filter (a) of LS bypass plug (3) on the P1 side through orifice (b) to tank circuit T. • The hydraulic oil PLS2 flows from tip filter (a) of LS bypass plug (2) on the P2 side through orifice (b) to tank circuit T.
10-141 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
LS selector valve (only PC78US-6 without blade) Function • When the machine swings and the boom is raised simultaneously, this valve prevents the high-pressure swing LS pressure from entering LS circuit PLS and secures sufficient pump discharge amount to keep the boom raising speed. Operation 1. During normal operation
• •
When the boom is not raised, the pilot pressure is not applied to pilot port BP. Under this condition, pump discharge pressure PP is introduced through the internal passage of spool (1) into reducing valve (3) of the swing valve. When the swing lever is operated, LS pressure PLS is generated according to the load pressure and sent to the pump LS valve.
10-142 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
2. When machine swings and boom is raised simultaneously.
• •
•
•
When the machine swings and boom is raised simultaneously, the signal pressure of the boom RAISE PPC circuit is applied to pilot port BP. When pilot pressure BP acts on spool (1) and increases above the force of spring (2), spool is pushed to the right and the internal passage is closed, then pump discharge pressure PP does not flow into reducing valve (3) of the swing valve. As a result, swing LS pressure PLS is not generated and only the boom RAISE LS pressure is introduced in the pump LS valve to control the pump discharge amount. The level of pilot pressure BP is decided by the stroke of the control lever (Boom RAISE)
PC78US-6
10-143 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Boom raise merge valve (PC78US-6 with blade, PC78UU-6) During normal operation
When machine swings and boom is raised simultaneously
Function • When the machine swings and the boom is raised simultaneously, this valve merges discharge amount of the gear pump into that of main pump to heighten the boom raising speed. Operation 1. During normal operation • When the boom is not raised, the pilot pressure is not applied to pilot port BP. • Under this condition, gear pump circuit P3 and main pump circuit PP are shut off by spool (1), so oil in gear circuit P3 is not merged into that of main pump circuit PP.
10-144 (10)
2. When machine swings and boom is raised simultaneously • When the machine swings and boom is raised simultaneously, the signal pressure of the boom RAISE PPC circuit is applied to pilot port BP. • When pilot pressure BP acts on spool (1) and increases above the force of spring (2), spool is pushed to the right. Then, check valve (3) in spool (1) is pushed open and oil in gear pump circuit P3 is merged into that in main pump circuit PP to heighten the boom raising speed.
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Area ratio of pressure compensation valve
Function • The pressure compensation valve determines the compensation characteristics by carrying out fine adjustment of the area r atio (S2/S1) between (left) area S1 of flow control valve (2) and (right) area S2 of reducing valve (1) to match the characteristics of each actuator. S1: Area of flow control valve (2) – area of piston (3) S2: Area of reducing valve (1) – area of piston (3)
PC78US-6
Area ratio (S1:S2) and compensation characteristics • When ratio is 1.00: [Pump discharge pressure PP – spool notch upstream pressure PPB] = [LS circuit pressure PLS – actuator circuit pressure PA (= A)] and oil flow is divided in proportion to area of opening of spool. • When ratio is more than 1.00:PP – PPB > PLS – PA ( = A) and oil fl ow i s divided in a proportion less tha n ar ea of ope ning of spool. • When ratio is less than 1.00:PP – PPB < PLS – PA ( = A) and oil fl ow i s divided in a proportion more tha n ar ea of ope ning of spool.
10-145 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Pressure compensation valve
Function • During compound operations, if the load pressure on either actuator becomes lower than the other actuator and the oil flow is about to increase, compensation is made. [When this happens, the other actuator being used for compound operation (right side) is at a high load than the actuator on this side (left side).] Operation • When the load pressure on the other actuator (right side) becomes higher during compound operations, the oil flow in actuator circuit A on this side (left side) starts increasing. • When this happens, the LS pressure PLS on the other actuator acts on spring chamber PLSS, and reducing valve (1) and flow control valve (2) are pushed to the left. • Flow control valve (2) throttles the area of opening between pump circuit PP and spool upstream PPA to cause a pressure loss between PP and PPA.
10-146 (10)
•
•
Flow control valve (2) and reducing valve (1) are balanced in a position where the difference between PLS and PA acting on both ends of reducing valve (1) and the pressure loss made between PP and PPA on the sides of flow control valve (2) will be the same. In this way, the pressure difference between upstream pressure PPA and downstream pressure PA of both spools used during compound operations is the same, so the pump flow is divided in proportion to the area of opening of notch (a) of each spool.
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Boom hydraulic drift prevention valve Function • This valve prevents the oil in the boom cylinder bottom from leaking through spool (1) to cause hydraulic drift of the boom while the boom control lever is not operated. 1. When boom is raised
Operation • When the boom is "raised", the main pressure from the control valve pushes up puppet (2). As a result, the hydraulic oil from the control valve flows through the valve into the boom cylinder bottom.
PC78US-6
10-147 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
2. When boom is held
•
When the boom control lever is returned to the neutral position after the boom is raised, the holding pressure on the boom cylinder bottom side is closed by puppet (2) and the hydraulic oil that flowed through orifices (a1) and (a2) is closed by pilot spool (3). Accordingly, the boom is held.
10-148 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
3. When boom is lowered
•
•
•
When the boom is lowered, pilot pressure P1 from the PPC valve pushes pilot spool (3) and the hydraulic oil in chamber (b) in the puppet is drained. The pressure in port (Ab) is heightened by the hydraulic oil from the boom cylinder bottom, but the pressure in chamber (b) is lowered by orifices (a1) and (a2). When the pressure in chamber b lowers below that in port (Ab), puppet (2) opens and the hydraulic oil from port (Ab) flows through port (Aa) into the control valve.
PC78US-6
10-149 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Boom regeneration circuit 1. When boom is lowered by its weight.
Function • While the boom is being lowered by its weight, if bottom pressure A of cylinder (1) is higher than head pressure B, this circuit sends the return oil on the bottom side to the head side to increase the cylinder speed by that amount.
•
•
When this happens, a part of the return oil on the bottom side flows through regeneration passages (a) of bottom spool (2), pushes check valve (3) open, and flows into the head side. As a result, the boom lowering speed is heightened.
Operation • While the boom is being lowered by its weight, pressure A on the bottom side of boom cylinder (1) is higher than pressure B on the head side.
10-150 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
2. When boom is lowered under a load.
Function • While the boom is being lowered under a load, if head pressure B of cylinder (1) is higher than bottom pressure A, check valve (3) is closed to shut off the head side and bottom side from each other. Operation • While the boom is being lowered under a load, pressure B on the head side of boom cylinder (1) is higher than pressure A on the bottom side. • When this happens, check valve (3) is closed by pressure B on the head side and spring (4) to shut off the head side and bottom side from each other.
PC78US-6
10-151 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Travel junction valve (L.H., R.H. travel junction circuit) 1. When traveling in a straight line
10-152 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
2. When steered during travel
PC78US-6
10-153 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Function • To compensate for any difference in the oil flow in the left and right travel circuits while machine travels in a straight line, the junction circuit opens when the left and right travel spools are operated. • In this way, the flow rates of oil to the left and right travel motors are almost the same when the machine travels in a straight line, so the machine deviates less. • When the machine is steered, the junction circuit opens. Since opening (b) of travel junction valve spool (3) is small, however, the junction circuit does not affect the steering performance. Operation 1. When traveling in a straight line • Since only both travel valves are operated and any work equipment valve is not operated, pump discharge circuits PP1 and PP2 and LS circuits PLS1 and PLS2 are separated by the pump merge-divider spool. (See the section on the LS bypass plug). • When both travel spools (1) are operated, the oil from the pump flows from pump discharge circuits PP1 and PP2 through actuator circuit PB to B. • When the machine travels in straight line, both reducing valves (2) are pushed to the right and notch (a) and travel junction circuit are opened. • The right end of travel junction spool (3) is the work equipment PPC pressure circuit. Since the work equipment valve is not operated at this time, however, any pressure is not generated. • In this way, both travel actuator circuits are interconnected by the travel junction circuit. If any difference occurs in the flow of oil to both travel motors, the difference is compensated to reduce travel deviation. 2. When steered during travel • Since only both travel valves are operated and any work equipment valve is not operated, pump discharge circuits PP1 and PP2 and LS circuits PLS1 and PLS2 are separated by the pump merge-divider spool. (See the section on the LS bypass plug). • The machine is steered by supplying the demand flow to the actuator circuit according to the strokes of both travel spools. (See the section on the unload valve.) • While the machine is traveling in a straight line, if the right travel spool (right 1) is returned to the neutral position and the machine is steered, a difference (left B > right B) is made between the load pressures in both travel actuator circuits PB.
10-154 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
Travel LS bleed circuit and travel junction valve 1. During normal operation
PC78US-6
10-155 (10)
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
CLSS
2. When travel actuator and another actuator are operated
10-156 (10)
PC78US-6
STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
Function • When the travel actuator and another actuator are operated at the same time, the amount of oil discarded through the throttle in LS circuit PLS increases and the pressure compensation precision of the travel circuit is lowered to reduce the drop of the travel speed. • When the travel actuator or any other actuator is operated singly, the LS bleed circuit is closed. • Travel junction valve spool (5) is set to open (b) (small) or open (c) (large) by the boom PPC pressure so that the difference between the flow rates in both travel circuits can be corrected easily.
CLSS
•
•
As a result, reducing valve (2) moves to the left and LS pressure PLS flows through check valves (3) and (4) and notch (a) of reducing valve (2) to travel circuit PB. For this reason, LS circuit pressure PLS, which is the same pressure as boom circuit pressure A, flows to travel circuit B to reduce the pressure.
Operation 1. During normal operation • When boom spool (1) is operated, LS circuit PLS becomes the same pressure as boom circuit pressure A. • Since the work equipment valve is operated, pump discharge pressures PP1 and PP2 are merged by the pump merge-divider valve spool. LS pressures PLS1, PLS2, and PLS3 are also merged. (See the sections on the pump merge-divider valve and logic valve.) • At the same time, LS pressure PLS also goes to spring chamber PLSS of reducing valve (2) of the travel valve. • Since the travel valve spool is not operated, notch (a) of reducing valve (2) is closed, and check valves (3) and (4) of the bleed circuit are also closed. • As a result, when the boom is operated singly, the travel LS bypass circuit is closed. 2. When travel actuator and another actuator are operated • When boom spool (1) is operated, LS circuit PLS becomes the same pressure as boom circuit pressure A. • Since the work equipment valve is operated, pump discharge pressures PP1 and PP2 are merged by the pump merge-divider valve spool. LS pressures PLS1, PLS2, and PLS3 are also merged. (See the sections on the pump merge-divider valve and logic valve.) • As for the actuator circuit pressure, the boom RAISE pressure is normally higher than the travel pressure (A > B), so the pressure in spring chamber PLSS inside reducing valve (2) of the travel valve is higher than travel circuit pressure PB.
PC78US-6
10-157 (10)
90 OTHERS HYDRAULIC CIRCUIT DIAGRAM PC78US-6 Serial No.: 4001 – 6500 (Blade-less specification)........... 90- 3 PC78US-6 Serial No.: 6501 and up (Blade-less specification).......... 90-3-2 PC78US-6 (Additional attachment circuit)........................................... 90- 5 PC78US-6 Serial No.: 4001 – 6500 (Blade specification) .................. 90- 7 PC78US-6 Serial No.: 6501 and up (Blade specification) ................. 90-7-2 PC78US-6 Serial No.: 4809 – 6500 (Norway & EU specification) ..... 90-7-4 PC78US-6 Serial No.: 6501 and up (Norway & EU specification) ..... 90-7-6 PC78UU-6.......................................................................................... 90-7-8 ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 4001 – 5500 (1/2)........................................... 90- 9 PC78US-6 Serial No.: 4001 – 5500 (2/2)............................................90-11 PC78US-6 Serial No.: 5501 – 6500 (1/2)........................................... 90-13 PC78US-6 Serial No.: 5501 – 6500 (2/2)........................................... 90-15 PC78US-6 Serial No.: 6501 and up (1/2)....................................... 90-15-2 PC78US-6 Serial No.: 6501 and up (2/2)....................................... 90-15-4 PC78US-6 Serial No.: 4809 – 5500 (Norway & EU specification) (1/2) ..................................................... 90-17 PC78US-6 Serial No.: 4809 – 5500 (Norway & EU specification) (2/2) ..................................................... 90-19 PC78US-6 Serial No.: 5501 – 6500 (Norway & EU specification) (1/2) ..................................................... 90-21 PC78US-6 Serial No.: 5501 – 6500 (Norway & EU specification) (2/2) ..................................................... 90-23 PC78US-6 Serial No.: 6501 and up (Norway & EU specification) (1/2) .................................................. 90-23-2 PC78US-6 Serial No.: 6501 and up (Norway & EU specification) (2/2) .................................................. 90-23-4 PC78UU-6 Serial No.: 22832 – 23500 (1/2)....................................... 90-25 PC78UU-6 Serial No.: 22832 – 23500 (2/2)....................................... 90-27 PC78UU-6 Serial No.: 23501 and up (1/2)......................................... 90-29 PC78UU-6 Serial No.: 23501 and up (2/2)......................................... 90-31
PC78US-6
90-1
HYDRAULIC CIRCUIT DIAGRAM PC78US-6 Serial No.: 4001 – 6500 (Blade-less specification)
PC78US-6
*1. Serial No.: 4001 – 4248 *2. Serial No.: 4249 and up
*3. Serial No.: 4001 – 5500 *4. Serial No.: 5501 and up
90-3 (10)
HYDRAULIC CIRCUIT DIAGRAM PC78US-6 (Additional attachment circuit)
PC78US-6
90-5
HYDRAULIC CIRCUIT DIAGRAM PC78US-6 Serial No.: 6501 and up (Blade-less specification)
PC78US-6
90-3-2 (10)
HYDRAULIC CIRCUIT DIAGRAM PC78US-6 Serial No.: 4001 – 6500 (Blade specification)
PC78US-6
*1. Serial No.: 4001 – 4248 *2. Serial No.: 4249 and up
*3. Serial No.: 4001 – 5500 *4. Serial No.: 5501 and up
90-7 (10)
HYDRAULIC CIRCUIT DIAGRAM PC78US-6 Serial No.: 6501 and up (Blade specification)
PC78US-6
90-7-2 (10)
HYDRAULIC CIRCUIT DIAGRAM PC78US-6 Serial No.: 4809 – 6500 (Norway & EU specification)
PC78US-6
*1. Serial No.: 4809 – 5500 *2. Serial No.: 5501 and up
90-7-4 (14)
HYDRAULIC CIRCUIT DIAGRAM PC78US-6 Serial No.: 6501 and up (Norway & EU specification)
PC78US-6
90-7-6 (14)
HYDRAULIC CIRCUIT DIAGRAM PC78UU-6
PC78US-6
*1. Serial No.: 22832 – 23500 *2. Serial No.: 23501 and up
90-7-8 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 4001 – 5500 (1/2)
PC78US-6
90-9
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 4001 – 5500 (2/2)
PC78US-6
90-11
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 5501 – 6500 (1/2)
PC78US-6
90-13 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6Serial No.: 5501 – 6500 (2/2)
PC78US-6
90-15 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 6501 and up (1/2)
PC78US-6
90-15-2 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 6501 and up (2/2)
PC78US-6
90-15-4 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 4809 – 5500 (Norway & EU specification) (1/2)
PC78US-6
90-17 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 4809 – 5500 (Norway & EU specification) (2/2)
PC78US-6
90-19 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 5501 – 6500 (Norway & EU specification) (1/2)
PC78US-6
90-21 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 5501 – 6500 (Norway & EU specification) (2/2)
PC78US-6
90-23 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 6501 and up (Norway & EU specification) (1/2)
PC78US-6
90-23-2 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78US-6 Serial No.: 6501 and up (Norway & EU specification) (2/2)
PC78US-6
90-23-4 (10)
ELECTRICAL CIRCUIT DIAGRAM PC78UU-6 Serial No.: 22832 – 23500 (1/2)
PC78US-6
90-25
ELECTRICAL CIRCUIT DIAGRAM PC78UU-6 Serial No.: 22832 – 23500 (2/2)
PC78US-6
90-27
ELECTRICAL CIRCUIT DIAGRAM PC78UU-6 Serial No.: 23501 and up (1/2)
PC78US-6
90-29
ELECTRICAL CIRCUIT DIAGRAM PC78UU-6 Serial No.: 23501 and up (2/2)
PC78US-6
90-31
