IMPLEMENT AND STEERING HYDRAULIC SYSTEM CONTINUED
Bulldozer Lift Control Valve
The bulldozer lift control valve is located between the steering control valve and the bulldozer tilt control valve in
the valve stack.
Pilot supply oil from the pilot control valve is used to control the position of the control valve spool. When the pilot
supply oil with sufficient pressure enters the bulldozer lift control valve at port control, the valve spool is shifted to
the left causing the pilot supply oil at the opposing end of the control valve spool to flow out of the port. This oil
flows to the pilot control valve and to the tank. When the spool is shifted to the left, the valve is in the RAISE
Similarly, when pilot supply oil with sufficient pressure enters the bulldozer lift control valve at pilot port #1 the
control valve spool is shifted to the right. This action causes the pilot supply oil at the opposing end of the control
valve spool to flow out of pilot port #2. This oil flows to the pilot control valve and to the tank. When the spool is
shifted to the right, the valve is in the LOWER position.
The lift valve has four positions.
The bulldozer lift control valve is spring centered. The springs that are located at the left end of the control valve
spool to keep the spool in the HOLD position when the lift circuit is not active.
The resolver is a two-way check valve. Signal oil from the previous resolver enters signal oil passage #2. The
resolver compares the pressure signal that is between the bulldozer lift control valve and the following control
valve. The pressure signal from the bulldozer lift control valve enters the resolver through passage #1. The higher
pressure of signal oil exits signal oil passage #3.
a. Flow Control Valve
Flow control valve limits the maximum flow of the oil to the lift circuit. As the oil flows from passage #5 to either rod
end passage or head end passage, the design of control valve spool causes a pressure drop. The left end of flow
control valve is at the same pressure as passage #5. 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 passage #5 through control valve
spool to the cylinders, the pressure differential between the left and the right ends of flow control valve increases.
Flow control valve moves to the right against the spring, closing off metering slots and reducing pump oil flow
into passage #5 through the load check valve. The flow control valve limits the flow of oil to the lift cylinders at
50 US gal./min (190 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
Pressure limiter valve is used in the bulldozer lift control valve in order to limit the pressure to the lift circuit.
The pressure setting of the pressure limiter valve is 3,300 ± 45 psi (22,750 ± 300 kPa).
When the bulldozer lift control valve is in an operating position, cylinder oil flows through passage and the oil
becomes signal oil. Signal oil flows to the chamber and then to the resolver and through passage #4 to spring