HOLD Position
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| Illustration 1 | g00875530 |
HOLD position for the stick valve (1) Rod end line relief valve, (2) Spool, (3) Chamber for pilot oil, (4) Spring, (5) Passage to tank, (6) Signal passage, (7) Chamber, (8) Load check valve, (9) Passage, (10) Pump passage, (11) Hole, (12) Passage, (13) Hole, (14) Spring, (15) Chamber, (16) Signal passage, (17) Passage to tank, (18) Signal line to the next valve, (19) Secondary resolver, (20) Signal line from the previous valve, (21) Primary resolver, (22) Chamber for pilot oil, (23) Spring, (24) Head end line relief valve, (25) Port to head end, (26) Passage, (27) Boom cylinder, (28) Check valve, (29) Passage, (30) Port to rod end, (31) Pilot passage, (32) Chamber, (33) Piston, (34) Ball check valve, (35) Chamber, (A) Pump oil, (B) Return oil, (C) Blocked oil and (D) Pilot oil The boom control valve is located between the auxiliary control valve and the swing control valve. | |
In the HOLD position, spool (2) blocks pressure oil in passage (12) from flowing to passages (26) and (29). Spool (2) is centered by spring (4) and spring (23) .
The oil from the pump enters the passage (10). Passage (10) is common in all sections of the valves and the passage has no outlet. Oil flows into passage (9) through hole (11) in load check valve (8). The oil then flows into chamber (7) .
Pressure in chamber (7) rises and the pressure acts against load check valve (8). When the pressure overcomes the force of the spring (14) and the pressure in chamber (15), the pressure causes load check valve (8) to move to the left.
As the load check valve (8) moves to the left, oil flows from passage (10) into passage (12). The oil in passage (12) is blocked by spool (2) until the operator moves the control lever.
The oil in passage (12) enters hole (13). The oil flows into chamber (15). The combination of oil in chamber (15) and the spring (14) cause the load check valve (8) to move to the right. Load check valve (8) blocks oil from entering passage (12).
Passage (6) is open to the tank through passage (5). Passage (16) is open to the tank through passage (17). The return to the tank passage is common in all control valves.
The check valve (28) blocks the oil in port (29). The spool (2) blocks the oil in port (25) .
LOWER Position
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| Illustration 2 | g00875531 |
LOWER position for the stick valve (1) Rod end line relief valve, (2) Spool, (3) Chamber for pilot oil, (4) Spring, (5) Passage to tank, (6) Signal passage, (7) Chamber, (8) Load check valve, (9) Passage, (10) Pump passage, (11) Hole, (12) Passage, (13) Hole, (14) Spring, (15) Chamber, (16) Signal passage, (17) Passage to tank, (18) Signal line to the next valve, (19) Secondary resolver, (20) Signal line from the previous valve, (21) Primary resolver, (22) Chamber for pilot oil, (23) Spring, (24) Head end line relief valve, (25) Port to head end, (26) Passage, (27) Boom cylinder, (28) Check valve, (29) Passage, (30) Port to rod end, (31) Pilot passage, (32) Chamber, (33) Piston, (34) Ball check valve, (35) Chamber, (A) Pump oil, (B) Return oil, (C) Blocked oil and (D) Pilot oil | |
When the operator places the joystick into the LOWER position, pilot oil flows into chamber (22). The pilot oil in chamber (22) compresses spring (4). This allows the spool (2) to move to the right.
Pilot oil flows through passage (31) and into chamber (32). The pressure in chamber (32) will move piston (33) downward. Ball check valve (34) will unseat when piston (33) moves downward. The trapped oil in chamber (35) will be vented to the tank and check valve (28) will open. When check valve (28) opens, oil will flow from the rod end of the cylinder to tank when the rod extends.
For a given amount of lever movement, spool (2) will move a proportional amount because of the pilot oil that is sent into chamber (22) .
Pump oil from passage (12) flows around spool (2) and into passage (26). Oil in signal passage (16) is blocked from entering the passage to the tank (17). Oil in signal passage (16) senses the pressure in port (26). The oil in signal passage (16) flows to the primary resolver (21) .
The oil in the primary resolver (21) flows to the secondary resolver (19) and to the pump. This causes the pump to increase flow.
Load check valve (8) compares the pressure in chamber (7) to the signal pressure in chamber (15) and spring (14). When the pressure in chamber (7) is greater than the pressure in chamber (15) and force of spring (14) combined, load check valve (8) will move down and oil will be directed to passage (12). Spool (2) controls the amount of flow into passage (26) that is desired.
As pump flow increases, more oil flows past spool (2) through passage (26) and into port (25) for the head end of the boom cylinder.
This will cause the rod of the boom cylinder to extend and the boom will lower.
As the rod extends, oil flows from the rod end of the cylinder through port (30), past check valve (28), into passage (29), past the spool (2) and into passage (6). Then, the oil flows into passage (5) to the hydraulic tank.
If the pump supply pressure becomes less than the requirements for the work port, the load check valve (8) will move to the right in order to prevent boom cylinder drift. Check valve (28) also prevents the boom cylinder from drifting. Check valve (28) opens when pump supply pressure enters passage (26) or pilot pressure enters passage (31) .
When the operator releases the control lever, spring (3) moves the spool (2) to the HOLD position.
Refer to Systems Operation, "Makeup and Relief Valve" for the operation of relief valve (24) .
RAISE Position
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| Illustration 3 | g00875533 |
HOLD position for the stick valve (1) Rod end line relief valve, (2) Spool, (3) Chamber for pilot oil, (4) Spring, (5) Passage to tank, (6) Signal passage, (7) Chamber, (8) Load check valve, (9) Passage, (10) Pump passage, (11) Hole, (12) Passage, (13) Hole, (14) Spring, (15) Passage, (16) Signal passage, (17) Passage to tank, (18) Signal line to the next valve, (19) Secondary resolver, (20) Signal line from the previous valve, (21) Primary resolver, (22) Chamber for pilot oil, (23) Spring, (24) Head end line relief valve, (25) Port to head end, (26) Passage, (27) Boom cylinder, (28) Check valve, (29) Passage, (30) Port to rod end, (31) Pilot passage, (32) Chamber, (33) Piston, (34) Ball check valve, (35) Chamber, (A) Pump oil, (B) Return oil, (C) Blocked oil and (D) Pilot oil | |
When the operator places the joystick into the RAISE position, pilot oil flows into chamber (3). The pilot oil in chamber (3) compresses spring (23). This allows the spool (2) to move to the left.
For a given amount of lever movement, spool (2) will move a proportional amount because of the pilot oil that is sent into chamber (3) .
Pump oil from passage (12) flows around spool (2) and into passage (29). Oil in signal passage (6) is blocked from entering the passage to the tank (5). Oil in signal passage (6) senses the pressure in port (29). The oil in signal passage (6) flows to the primary resolver (21) .
The oil in the primary resolver (21) flows to the secondary resolver (19) and to the pump. This causes the pump to increase flow.
Load check valve (8) compares the pressure in chamber (7) to the signal pressure in chamber (15) and spring (14). When the pressure in chamber (7) is greater than the pressure in chamber (15) and force of spring (14) combined, load check valve (8) will move down and oil will be directed to passage (12). Spool (2) controls the amount of flow into passage (29) that is desired.
As pump flow increases, more oil flows past spool (2) to passage (29) .
As the pressure in passage (29) rises, the pressure opens check valve (28). Check valve (28) allows oil to flow into the port for the rod end of the boom cylinder (30). This will cause the rod of the boom cylinder to retract and the boom will raise.
As the rod retracts, oil flows from the head end of the cylinder through port (25) and into passage (26). Then, the oil flows through passage (6) and into passage (5) to the hydraulic tank.
When the operator releases the control lever, spring (23) and spring (4) move the spool (2) to the HOLD position.
Refer to Systems Operation, "Makeup and Relief Valve" for the operation of valve (1) .