IMPLEMENT AND STEERING HYDRAULIC SYSTEM CONTINUED
Control Valve (Bulldozer Tilt)
a. Flow Control Valve
The flow control valve limits the maximum flow of the oil to the tilt circuit. As the oil flows from passage to either rod
end passage or head end passage, the design of the control valve spool causes a pressure drop. The left end of
the flow control valve is at the same pressure as the passage. The right end of the flow control valve is at the same
pressure as either rod end passage or head end passage. As the flow increases from the passage through the
control valve spool to the cylinders, the pressure differential between the left and the right ends of the flow control
valve increases. The flow control valve moves to the right against spring #1, closing off metering slots and reducing
pump oil flow into the passage through the load check valve. The flow control valve limits the flow of oil to the tilt
cylinders at 21 US gal./min (80 L/min).
N OT E
Different designs of the control valve stem that are used in the various valves change the
limits of the maximum flow into the various cylinders.
b. Pressure Limiter Valve Operation
The pressure limiter valve is used in the bulldozer tilt control valve in order to limit the pressure to the tilt circuit. The
pressure setting of the pressure limiter valve is 2,500 ± 45 psi (17,225 ± 300 kPa).
When the bulldozer tilt control valve is in an operating position, cylinder oil flows through the passage and the oil
becomes signal oil. Signal oil flows to the chamber then to the resolver.
When the signal oil pressure in spring chamber #1 reaches approximately 2,500 psi (17,225 kPa), the spool in the
pressure limiter valve moves from the valve seat. Oil is sent through the outlet passage to the tank.
The system oil causes the flow control valve to move to the right. The flow of pump oil to the tilt circuit decreases
until the pressure of the cylinder oil decreases.
c. Load Check Valve
The load check valve prevents reverse oil flow in the tilt cylinder which can cause cylinder drift or load loss. The
load check valve will not open until system pressure in chamber #2 creates a force against the load check spring
#2 that is higher than the opposing force against the other side of the check valve. The opposing force is the sum
of the force of spring and the force that is created by the oil pressure in the passage.