Note: This hydraulic arrangement pertains to the single action one pump arrangement and to the double action one pump arrangement.
In the one pump flow system, the attachment circuit oil is supplied by the front pump. The two pump flow system allows the attachment circuit to share rear pump oil and front pump oil. This system offers the following benefits: increased oil flow to the attachment and reduced load on the front pump. The two pump flow system consists of pilot lines and a front lines group.
Inactive Boom Raise Circuit
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| Illustration 1 | g00385453 |
Pilot Oil Lines (1) Pilot valve (2) Pilot line from attachment valve to pilot valve (3) Main control valve (4) Port to attachment control valve (5) Return line to pilot oil manifold (6) Pilot oil supply line (7) Pilot oil manifold (8) Pilot line to the bottom of Boom II control valve (9) Pilot line to the top of Boom II control valve | |
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| Illustration 2 | g00385464 |
Pilot valve (1) (10) Passage from attachment control valve (11) Passage to top of Boom II control valve (12) Spring (13) Passage to drain (14) Spool (15) Passage to bottom of Boom II control valve | |
Pilot supply oil from pilot manifold (7) goes through line (6) . The oil then enters the attachment control valve through port (4) . When the attachment is not being used, the pilot oil passes through the stem in the main control valve. The oil then goes to the drain.
When the pedal for the attachment is operated, the stem is shifted. The shifting of the stem blocks the flow of pilot oil through the stem. The pilot oil then flows through the tee at port (4) . The pilot oil goes through line (2) to pilot valve (1) and passage (10) . The pilot oil in passage (10) flows around spool (14) and out passage (15) .
The pilot oil now flows through line (8) to the bottom of the Boom II control valve. The pilot oil shifts the Boom II control valve stem upward. While the stem is shifted, the front pump oil is blocked from flowing through the center passage in the stem. While the front pump oil is blocked, the pressure in the front pump increases.
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| Illustration 3 | g00385592 |
Front Lines Group (3) Main control valve (16) Check valve group (17) Line from the front pump to main control valve (18) Tee (19) Line from the front pump to attachment control valve | |
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| Illustration 4 | g00385636 |
Check valve group (16) Check valve group (20) Passage (21) Spring (22) Valve (23) Passage | |
The front lines group contains tee (18) and line (17) . Tee (18) and line (17) supply front pump oil to main control valve (3) . While the Boom II control valve is shifted, front pump oil is sent through line (19) to check valve (16) .
Valve (22) shifts to the right when the pressure of the front pump oil is greater than the combined force of spring (21) and the pressure in passage (20) . This allows the front pump oil to flow through passage (20) to the attachment control valve to join with the rear pump oil.
Valve (22) shifts to the left when the pressure of the front pump oil is less than the combined force of spring (21) and the pressure in passage (20) . This stops the supply of front pump oil the to the attachment circuit.
Active Boom Raise Circuit
With an active boom raise circuit, the front pump and the rear pump are required to operate the boom. Pilot oil is sent to the bottom the boom control valve stems and passage (11) of pilot valve (1) . The pilot oil moves spool (14) to the left. This closes the connection between passages (10) and (15) , but this opens the connection between passage (15) and (13) . Now the pilot oil in line (9) and the top of Boom II control valve can go through passage (15) and out passage (13) of pilot valve (1) . The pilot oil then goes through line (5) to pilot oil manifold (7) and to the drain.
While the pilot oil is at the top of the Boom II control valve and open to drain, the boom control stem shifts upward. Then, the front pump oil is sent to the boom. The attachment circuit does not get front pump oil when the boom raise circuit is fully activated. The attachment circuit will get oil if the pressure in the boom circuit is less than the pressure in the attachment circuit. The boom circuit has priority over the attachment circuit.