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| Illustration 1 | g00843246 |
When the machine is equipped with a bulldozer and with a ripper, the ripper lift control valve is the third 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 (7), resolver (12), flow control valve (16), load check valve (19) 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 (3) 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 (12) is a double check valve. Flow control valve (16) limits the maximum flow of oil to the lift 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 (7) are in separate sections.
Load Check Valve
Load check valve (19) prevents reverse oil flow in the ripper lift 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 (7) is in the head end of the lift circuit. The makeup valve opens when cylinder oil pressure in head end passage (6) drops 14 kPa (2 psi) below the return oil pressure in outlet passage (8). Makeup valve (7) adds return oil from outlet passage (8) to cylinder oil in head end passage (6). The additional oil prevents cavitation (vacuum) in the lift cylinders.
HOLD Position
When the control valve spools are in the HOLD position, pump oil flows to the inlet passage. Oil flows around flow control valve (16) and oil flows in primary metering slots (17). Since there is no signal oil in chamber (14) to move flow control valve (16) to the left, no oil will flow 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 (5), (6) and (20) are blocked.
RAISE Position
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| Illustration 2 | g00843249 |
When pilot control pressure causes valve spool (22) to move to the RAISE position, cylinder oil from passage (6) flows through passage (4) to chamber (10). The oil functions as signal oil. The signal oil opens resolver (12) and flows to chamber (14). The oil in chamber (14) moves flow control valve (16) to the left. The oil flows to the next control valve, to the inlet manifold, and to the compensator valve on the pump.
The increase of pump oil flow to inlet passage (15) opens load check valve (19). The oil flows through load check valve (19). The oil then flows through passage (20) around valve spool (22) and out passage (6) to the rod ends of the ripper lift cylinders. The ripper lift cylinders then raise 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 (9) to the oil tank.
LOWER Position
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| Illustration 3 | g00843258 |
When pilot control pressure causes valve spool (22) to move to the LOWER position, cylinder oil from head end passage (5) flows through passage (4) to chamber (10). The oil functions as signal oil. The signal oil opens resolver (12) and flows to chamber (14). The oil in chamber (14) moves flow control valve (16) to the left. The signal oil flows to the next control valve, to the inlet manifold, and to the compensator valve on the pump.
The increase of pump oil flow to inlet passage (15) opens load check valve (19). The oil flows through load check valve (19). The oil then flows around valve spool (22) and out passage (5) to the head ends of the ripper lift cylinders. The ripper lift cylinders then lower the ripper.
Return oil from the rod ends of the ripper lift cylinders flows through passage (6), around valve spool (22), through outlet passage (21), and to the oil tank.