IMPLEMENT AND STEERING HYDRAULIC SYSTEM CONTINUED
Control Valve (Ripper Tip)
When the machine is equipped with a bulldozer and with a ripper, the ripper tip control valve is the fifth valve in the
valve stack and controls the angle of insertion of the ripper. The control valve is equipped with these components:
makeup valve, resolver, pressure limiter valve, load check valve, and valve spool.
The ripper tip control valve is spring centered. The control valve spool is a closed center spool and a pilot operated
spool with three positions: TIP IN, HOLD, and TIP OUT. A spring 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 the valve spool.
The resolver 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 the makeup valve, pressure
limiter valve, and load check valve are in the following separate sections:
a. Load Check Valve
The load check valve prevents reverse oil flow in the ripper tip cylinders, which can cause cylinder drift or load loss.
The load check valve does not open until the pump oil pressure in chamber #3 overcomes the force of the spring
for the load check valve and of the cylinder oil pressure in the passage.
b. Makeup Valve
The makeup valve is in the rod end of the tip circuit. The makeup valve opens when cylinder oil pressure in the
passage drops 2 psi (14 kPa) below the return oil pressure in the outlet passage. The makeup valve adds return oil
in the outlet passage to cylinder oil in the passage. The additional oil prevents cavitation (vacuum) in the tip
c. Pressure Limiter Valve Operation
Pressure limiter valve is used in the ripper tip control valve in order to limit the pressure to the tip circuit. The
pressure setting of the pressure limiter valve is 3,300 ± 45 psi (22,750 ± 300 kPa) 3,300 ± 45 psi.
When the ripper tip control valve is in an operating position, cylinder oil flows through the passage and the oil
becomes signal oil. Signal oil flows to chamber #1. Then, the oil flows to the resolver.
When the signal oil pressure in spring chamber #2 reaches approximately 3,300 psi (22,750 kPa), the spool in the
pressure limiter valve moves from the valve seat. Oil is sent through the outlet passage to the tank.
The signal oil causes the flow control valve to move to the right. The flow of pump oil to the tip circuit decreases
until the pressure of the cylinder oil decreases.