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| Illustration 1 | g00798180 |
When the machine is equipped with a bulldozer and with a ripper, the ripper tip control valve is the fourth valve in the valve stack. The ripper tip control valve changes the angle of the ripper from the vertical toward the machine. The control valve is equipped with these components: makeup valve (5), resolver (12), flow control valve (16), load check valve (19) and valve spool (22) .
The ripper tip control valve is a spring centered valve. Control valve spool (22) is a closed center spool and a pilot operated spool with three positions: TIP IN, HOLD and TIP OUT. Spring (3) keeps the valve spool in the HOLD position when the ripper tip 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 (12) is a double check valve. Flow control valve (16) limits the maximum flow of oil to the tip circuit. 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 function of load check valve (19) and of makeup valve (5) are in separate sections.
Load Check Valve
Load check valve (19) prevents reverse oil flow in the ripper tip cylinders, which can cause cylinder drift. The load check valve does not open until pump oil pressure in chamber (15) overcomes the force of the spring for the load check valve and of the cylinder oil pressure in passage (20) .
Makeup Valve
Makeup valve (5) is in the rod end of the tip circuit. The makeup valve opens when cylinder oil pressure in passage (6) drops 14 kPa (2 psi) below the return oil pressure in outlet passage (7). Makeup valve (5) adds return oil from outlet passage (7) to cylinder oil in passage (6). The additional oil prevents cavitation (vacuum) in the tip cylinders.
HOLD Position
When the control valve spools are in the HOLD position, pump oil flows to the inlet passage of the control valve. Oil flows around flow control valve (16) and oil flows in primary metering slots (17). Since there is no oil in chamber (14) to move flow control valve (16) to the left, no oil flows through the metering slots to open load check valve (19). Pump oil then flows through the outlet passage to the next control valve.
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 2950 kPa (410 psi). Passage (4), chamber (10), and resolver (12) are drained. Passages (6), (8) and (20) are blocked.
TIP OUT Position
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| Illustration 2 | g00798171 |
When pilot control pressure causes control valve spool (22) to move to the TIP OUT position, chamber (10) is blocked from outlet passage (9). Passage (4) is opened to passage (6). Cylinder oil from passage (6) flows through passage (4) to chamber (10). The oil functions as signal oil. Part of the signal oil flows to resolver (12) and through an orifice to the spring chamber behind flow control valve (16). The signal oil opens flow control valve (16). The rest of the signal oil flows through resolver (12) to the inlet manifold and to the compensator valve on the pump.
The increase of pump oil flow to the inlet passage flows through primary metering slots (17) into chamber (18). The pump oil opens load check valve (19). The oil flows through load check valve (19). The oil then flows through passage (20) around control valve spool (22) and out passage (6) to the rod ends of the tip cylinders. The tip cylinders then retract. The ripper tips outward.
Return oil from the head ends of the tip cylinders flows through passage (8), around control valve spool (22) and through outlet passage (9) to the oil tank.
TIP IN Position
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| Illustration 3 | g00795269 |
When pilot control pressure causes control valve spool (22) to move to the TIP IN position, chamber (10) is blocked from outlet passage (9). Passage (4) is opened to passage (8). Cylinder oil from passage (8) flows through passage (4) to chamber (10). The oil functions as signal oil. Part of the signal oil flows to resolver (12) and through an orifice to the spring chamber behind flow control valve (16). The signal oil opens flow control valve (16). The rest of the signal oil flows through resolver (12) to the inlet manifold and to the compensator valve on the pump.
The increase of pump oil flow to the inlet passage flows through primary metering slots (17) into chamber (18). The pump oil opens load check valve (19). The oil flows through load check valve (19). The oil then flows through passage (20) around control valve spool (22) and out passage (8) to the head ends of the tip cylinders. The tip cylinders then extend. The ripper tips inward.
Return oil from the rod ends of the tip cylinders flows through passage (6), around control valve spool (22), and through outlet passage (21) to the oil tank.