THEORY OF OPERATION - CONTINUED
HYDRAULIC SYSTEM - CONTINUED
TILT BACK Position.
When the tilt circuit is the only hydraulic circuit in operation, the tilt circuit will have the highest signal oil
pressure in the hydraulic system. When the pilot valve is moved to the TILTBACK position, pilot oil
enters the control valve through port (11). The pilot oil flows into chamber (10). As the pilot oil moves
spool (25) to the left, spring (24) is compressed. When the spool moves to the left, pump supply oil flows
from passage (15) over the metering slots in the spool into passage (17).
The hydraulic oil in passage (17) flows to pressure compensator valve (6) and passage (27). In the pressure
compensator valve, the hydraulic oil flows into internal passages. The pressure compensator valve moves
up. As the pressure compensator valve moves up, the cross-drilled passage is opened to passage (4). Some
of the hydraulic oil flows around the pressure compensator valve to spring (3). The hydraulic oil that flows
to spring and passage (4) is signal oil. Spring and the signal oil balance the pressure compensator valve
against the hydraulic oil pressure in passage (17). This controls the flow across spool (25).
The signal oil in passage (4) flows to the pressure compensator valve in each control valve. The signal oil
also flows to the pressure and flow compensator valve on the hydraulic pump. The signal oil helps to con-
trol the output of the hydraulic pump. The hydraulic pump upstrokes and the hydraulic oil pressure in pas-
sage (17) increases. When the hydraulic oil pressure in passage raises above circuit pressure, the hydraulic
oil unseats load check valve (20) and flows to passages (14 and 18).
In passage (18), the hydraulic oil flows around spool (25) into passage (16). From passage, the hydraulic
oil flows into passage (14). In passage, the hydraulic oil flows around spool (25) to passage (13). The
hydraulic oil then flows to the pilot operated check valve (12).
The hydraulic oil flows through the pilot operated check valve. Then, the hydraulic oil flows through port
(5) to the rod end of the tilt cylinder.
Hydraulic oil from the head end of the tilt cylinders flows to port (2). Then, the hydraulic oil flows to pas-
sage (19) around spool (25) to tank passage (21). Then, the hydraulic oil flows to the tank.
When the operator releases the pilot valve, the pilot oil flows to the right. Pilot operated check valve (12)
closes. Spring (24) moves spool (25) to the HOLD position. Pilot operated check valve and load check
valve (20) block the hydraulic oil in the hydraulic lines.