TM 5-3805-290-23-1
THEORY OF OPERATION - CONTINUED
0003 00
HYDRAULIC SYSTEM - CONTINUED
b.
DUMP Position.
(1)
When the tilt circuit is the only hydraulic circuit in operation, the tilt circuit will have the highest load sig-
nal pressure in the hydraulic system. When the pilot valve is moved to the DUMP position, pilot oil enters
the control valve through port (22). The pilot oil flows into chamber (23) and passage (26). As the pilot oil
moves spool (25) to the right, spring (9) is compressed. The pilot oil also opens the pilot operated check
valve (12). When the spool moves to the right, pump supply oil flows over the metering slots in the spool
and into passage (17).
(2)
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).
(3)
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).
(4)
Hydraulic oil flows from the rod end of the tilt cylinder to port (5). The hydraulic oil flows through the
port to the pilot operated check valve (12). The hydraulic oil flows through the check valve to passage
(13). The spool blocks the hydraulic oil from flowing to the passage (8).
(5)
In passage (14), the hydraulic oil flows around the spool into passages (16 and 18). The hydraulic oil com-
bines with the hydraulic oil from passage (27). All of the hydraulic oil flows into passage (19). The
hydraulic oil then flows through port (2) to the head end of the tilt cylinder.
(6)
In passage (13), the hydraulic oil flows around spool (25) into passages (16 and 18). Then, the hydraulic
oil combines with the hydraulic oil from passage (27) and flows to passage (19). The hydraulic oil flows
through port (2) to the head end of the tilt cylinder.
(7)
When the operator releases the pilot valve, the pilot oil flows toward the pilot valve and to the tank. Pilot
operated check valve (12) closes. Spring (9) moves spool (25) to the HOLD position. Pilot operated check
valve and load check valve (20) block the hydraulic oil in the hydraulic lines.
0003 00-170
