HOLD Position
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| Illustration 1 | g00878082 |
HOLD position for the boom valve (1) Rod end line relief valve, (2) Spool, (3) Passage to tank, (4) Signal passage, (5) Chamber, (6) Load check valve, (7) Passage, (8) Pump passage, (9) Hole, (10) Passage, (11) Hole, (12) Spring, (13) Chamber, (14) Signal passage, (15) Passage to tank, (16) Spring, (17) Line to the next valve, (18) Secondary Resolver, (19) Line from the previous valve, (20) Head end line relief valve, (21) Primary Resolver, (22) Port for the head end of the cylinder, (23) Port to rod end of the cylinder, (24) Hole, (25) Advance signal passage, (26) Hole, (A) Pump oil, (B) Return oil and (C) Blocked 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 (10) from flowing to ports (22) and (23). Spool (2) is centered by spring (16) .
Supply oil from the pump flows in the valve through passage (8). Passage (8) is common in all sections of the valves and the passage has no outlet. Oil flows into passage (7) through hole (9) in load check valve (6). The oil then flows into chamber (5) .
Pressure in chamber (5) rises and the pressure acts against load check valve (6). When the pressure overcomes the force of spring (12) and the pressure in chamber (13), the pressure causes load check valve (6) to move down. As the load check valve (6) moves down, oil flows from passage (8) into passage (10). The oil in passage (10) is blocked by spool (2) until the operator moves the control lever.
The oil in passage (10) enters hole (11). The oil flows into chamber (13). The combination of the oil in chamber (13) and the spring (12) causes the load check valve (6) to move up. Load check valve (6) blocks oil from entering passage (10).
RAISE Position
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| Illustration 2 | g00878083 |
RAISE position of the boom valve (1) Rod end line relief valve, (2) Spool, (3) Passage to tank, (4) Signal passage, (5) Chamber, (6) Load check valve, (7) Passage, (8) Pump passage, (9) Hole, (10) Passage, (11) Hole, (12) Spring, (13) Chamber, (14) Signal passage, (15) Passage to tank, (16) Spring, (17) Line to the next valve, (18) Secondary Resolver, (19) Line from the previous valve, (20) Head end line relief valve, (21) Primary Resolver, (22) Port for the head end of the cylinder, (23) Port to rod end of the cylinder, (24) Hole, (25) Advance signal passage, (26) Hole, (A) Pump oil, (B) Return oil and (C) Blocked oil | |
When the operator places the control lever in the RAISE position, spool (2) moves upward. Spring (16) is compressed.
For a given amount of lever movement, spool (2) will move a proportional distance.
As spool (2) moves upward, the pump oil in passage (10) flows around spool (2) into port (22). Oil in signal passage (14) is blocked from entering tank passage (15). Signal passage (14) senses the pressure in port (22). The oil in signal passage (14) flows to the primary resolver (21) .
The oil in the primary resolver (21) flows to the secondary resolver (18) and to the pump. This causes the pump to increase flow.
Load check valve (6) compares the pressure in chamber (5) to the signal pressure in chamber (13) and spring (12). When the pressure in chamber (5) is greater than the pressure in chamber (13) and force of spring (12) combined, load check valve (6) will move down and oil will be directed to passage (10). Spool (2) controls the amount of flow into head end of the boom cylinder that is desired.
As pump flow increases, more oil flows past spool (2) to the head end of the boom cylinder. The oil causes the rods to extend. When the rods extend, the rod causes the boom to raise.
As the rod extends, oil from the rod end of the cylinder flows from port (23), through passage (4) and into passage (3) to the hydraulic tank.
If the pump supply pressure becomes less than the requirements for the work port, the load check valve (6) will move upward in order to prevent stick cylinder drift.
When the control lever is released, spring (16) moves spool (2) downward into the HOLD position.
Refer to Systems Operation, "Makeup and Relief Valve" for the operation of valves (20) .
LOWER Position
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| Illustration 3 | g00878084 |
LOWER Position for the Boom Valve (1) Rod end line relief valve, (2) Spool, (3) Passage to tank, (4) Signal passage, (5) Chamber, (6) Load check valve, (7) Passage, (8) Pump passage, (9) Hole, (10) Passage, (11) Hole, (12) Spring, (13) Passage, (14) Signal passage, (15) Passage to tank, (16) Spring, (17) Line to the next valve, (18) Secondary Resolver, (19) Line from the previous valve, (20) Head end line relief valve, (21) Primary Resolver, (22) Port for the head end of the cylinder, (23) Port to rod end of the cylinder, (24) Hole, (25) Advance signal passage, (26) Hole, (A) Pump oil, (B) Return oil and (C) Blocked oil | |
When the operator places the control lever in the LOWER position, spool (2) moves downward. Spring (16) is compressed downward.
For a given amount of lever movement, spool (2) will move a proportional distance.
As spool (2) begins to move downward, oil fills advance signal passage (25) through hole (24). The oil from advance signal passage (25) flows through hole (26). The oil then flows into port (23) and signal passage (4). The advance signal passage allows signal pressure to be sent back to the pump in order to upstroke the pump. This will provide a better response to the demand of the work tool.
As the spool continues to move up, the pump oil in passage (10) flows around spool (2) into port (23). Oil in signal passage (4) is blocked from entering tank passage (3). Signal passage (4) senses the pressure in port (23). The oil in signal passage (4) flows to the primary resolver (21) .
The oil in the primary resolver (21) flows to the secondary resolver (18) and to the pump. This causes the pump to increase flow.
Load check valve (6) compares the pressure in chamber (5) to the signal pressure in chamber (13) and spring (12). When the pressure in chamber (5) is greater than the pressure in chamber (13) and force of spring (12) combined, load check valve (6) will move down and oil will be directed to passage (10). Spool (2) controls the amount of flow into rod end of the boom cylinder that is desired.
As pump flow increases, more oil flows past spool (2) to the rod end of the boom cylinder. The oil causes the rods to retract. When the rod retracts, the rod causes the boom to lower.
As the rod retracts, oil from the head end of the cylinder flows from port (22), through passage (14) and into passage (15) to the hydraulic tank.
If the pump supply pressure becomes less than the requirements for the work port, the load check valve (6) will move upward in order to prevent stick cylinder drift.
When the control lever is released, spring (16) moves spool (2) upward into the HOLD position.
Refer to Systems Operation, "Makeup and Relief Valve" for the operation of valves (1) .