THEORY OF OPERATION - CONTINUED
There are two pumps for the hydraulic system: implement and steering, and supplemental steering. The implement and
steering pump is powered through the transmission and is located on the upper-right front of the transfer case. This is a double-
section, vane-type pump. Rotation is clockwise (viewed from drive end). Rated output at 1,900 RPM: 56 gpm flow @ 2,250
psi (15,513 kPa) for the steering section, and 74 gpm flow @ 2,000 psi (13,790 kPa) for implement controls.
During normal operations a gear-type pump (supplemental steering pump), located beneath engine on front of case and
frame, adds to the volume of flow in implement hydraulics. Since this pump is ground-driven by forward motion of machine,
the amount of oil it adds is directly proportional to machine speed. If the implement/steering pump loses drive power, then the
supplemental steering pump supplies hydraulics for operation of steering only. This allows the machine, in motion, to be
steered safely to a stop.
Hydraulic Reservoir. Located on the right side of engine compartment, directly in front of the fuel tank. The reservoir
stores system hydraulic fluid for use by system components. Capacity is 29 gallons (110 L).
Filter. Located and mounted in the hydraulic reservoir. Receives hydraulic fluid at relief dump pressure, filters it, then
returns it to the system hydraulic reservoir. The filter has a built-in bypass valve. If the filter is full of dirt, and oil can
not easily pass through the element, there is an increase in the pressure of the oil. This opens the bypass valve, relieving
back pressure and preventing collapse of the element. Bypass also serves to allow oil to flow when temperatures are cold
and oil is thick.
Control Valve. A spool-operated, spring-centered, differential-pressure bank valve is located near the left side and on
top of the differential housing. Each of the separate control features (bowl, apron and ejector) have a separate spool. The
control levers for the scraper are on the right side of the operator seat. Rods and levers are used to connect the control
levers to the valve spools in the control valve. When one of the three implement valves is moved, fluid is circulated to
the respective implement. When all control levers are in the hold position, the fluid circulates through the control valve
then returns to the hydraulic tank.
Pressurized hydraulic fluid is directed to the separate systems by the control levers. Valve spools and internal porting
direct fluids to the necessary-outlets for positive control of hydraulic pressure. An internal relief valve keeps hydraulic
pressures from exceeding system capabilities.
Cylinders. Receive hydraulic fluid and convert pressure into mechanical force to either extend or retract the mechanical
Quick Drop and Check Valves. Mounted on bowl cylinders. Check valves operate by pilot signal pressure from control
valve. When activated, the check valves open to release pressurized fluid from the rod-end of the bowl cylinders. This
joins the flow from the hydraulic pump into the head-end of the cylinders. The additional flow through the cylinders
speeds up the lowering of the bowl.
Sequence Valve. This is a pressure relief valve for the rod end of the apron cylinder. This valve is mechanically set to a
relief pressure of 1,000 psi (6,895 kPa).
Due to the operating characteristics of the apron, relief pressure must be variable according to position. In its lowest
position, against the bowl stops, the relief pressure is at 1,000 psi. As the bowl is raised with the apron in the closed posi-
tion, mechanical linkages increase closure pressures on the apron. These pressures are variable with respect to apron/
bowl position. Tapped from bowl raise control valve pressures, a feedback pressure is sent to the sequence valve piston.
This pressure increases the mechanical relief pressure setting to a maximum of approximately 2,272 psi (15,665 kPa),
affording system components protection with increased pressure closing capabilities.