General Information
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| Illustration 1 | g00855149 |
When the machine is equipped with a bulldozer and with a ripper, the ripper lift control valve is the fourth valve in the valve stack. The ripper lift control valve controls the raising and the lowering of the ripper. The control valve is equipped with these components: makeup valve (4), resolver (11), pressure limiter valve (12), load check valve (20) and valve spool (22) .
The ripper lift control valve is a spring centered valve. Control valve spool (22) is a closed center spool and a pilot operated spool with three positions: RAISE, HOLD and LOWER. Spring (2) keeps the valve spool in the HOLD position when the ripper lift control valve is not active. Movement of the spool is controlled by the pilot control system. The pilot control system connects the ripper control lever to valve spool (22) .
Resolver (11) is a double check valve. The functions of the resolver and of the control valve spool are described in the sections on positions of the control valve. The descriptions of the functions of makeup valve (4), pressure limiter valve (12), and load check valve (20) are in the following separate sections.
Load Check Valve
Load check valve (20) prevents reverse oil flow in the ripper lift cylinders, which can cause cylinder drift or load loss. The load check valve does not open until pump oil pressure in passage (18) overcomes the force of the spring for the load check valve and of the cylinder oil pressure in passage (19) .
Makeup Valve
Makeup valve (4) is in the head end of the lift circuit. The makeup valve opens when cylinder oil pressure in passage (5) drops 14 kPa (2 psi) below the return oil pressure in outlet passage (6). Makeup valve (4) adds return oil in outlet passage (6) to cylinder oil in passage (5). The additional oil prevents cavitation (vacuum) in the lift cylinders.
Pressure Limiter Valve Operation
Pressure limiter valve (12) is used in the ripper lift control valve in order to limit the pressure to the lift circuit. The pressure setting of the pressure limiter valve is 19300 ± 300 kPa (2800 ± 45 psi).
When the ripper lift control valve is in an operating position, cylinder oil flows through passage (3) and the oil becomes signal oil. Signal oil flows to chamber (9). Then, the oil flows to resolver (11) .
When the signal oil pressure in spring chamber (14) reaches approximately 19300 kPa (2800 psi), the spool in pressure limiter valve (12) moves from the valve seat. Oil is sent through outlet passage (8) to the tank.
The signal oil causes flow control valve (16) to move to the right. The flow of pump oil to the tilt circuit decreases until the pressure of the cylinder oil decreases.
Basic Valve Operation
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| Illustration 2 | g00855149 |
When the control valve spools are in the HOLD position, pump oil flows to inlet passage (15). This passage is common to all sections of the valve stack and this passage has no outlet. Since all the valve spools are in the HOLD position, pump oil fills the parallel oil passages of the control valves. The pump maintains oil pressure at 3000 kPa (435 psi). Passage (3), chamber (9), and resolver (11) are drained. Passages (5), (7), and (19) are blocked.
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| Illustration 3 | g00856184 |
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| Illustration 4 | g00855370 |
When the pilot control pressure causes the valve spool (22) to move to the RAISE position, cylinder oil from passage (5) flows through passage (3) to chamber (9). The oil functions as signal oil. The signal oil opens resolver (11) and flows to the previous control valve and to the inlet manifold.
The increase of pump oil flow to inlet passage (15) opens load check valve (20). The oil flows through load check valve (20), through passage (19), and around valve spool (22). Then, the oil flows through passage (5) to the head ends of the ripper lift cylinders. The ripper lift cylinders then raise the ripper.
Return oil from the rod ends of the ripper lift cylinders flows through passage (7), around valve spool (22) and through outlet passage (8) to the tank.
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| Illustration 5 | g00856313 |
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| Illustration 6 | g00855371 |
When the pilot control pressure causes valve spool (22) to move to the LOWER position, cylinder oil from passage (7) flows through passage (3) to chamber (9). The oil functions as signal oil. The signal oil opens resolver (11). The signal oil flows to the previous control valve and to the inlet manifold.
The increase of pump oil flow to inlet passage (15) opens load check valve (20). The oil flows through load check valve (20). The oil then flows around valve spool (22) and out passage (7) to the rod ends of the ripper lift cylinders. The ripper lift cylinders then lower the ripper.
Return oil from the head ends of the ripper lift cylinders flows through passage (5), around valve spool (22), and through outlet passage (21) to the tank.