THEORY OF OPERATION - CONTINUED
HYDRAULIC SYSTEM - CONTINUED
When the auxiliary circuit is the only hydraulic circuit in operation, the auxiliary circuit will have the highest
hydraulic oil pressure in the hydraulic system. When the hydraulic oil exits the control valve through the port (2),
pilot oil enters the control valve through port (22). The pilot oil flows through the shock reducing check valve (21).
The shock reducing check valve moves to the right.
Pilot oil flows into chamber (23). As the pilot oil moves spool (25) to the right, spring (9) is compressed. When the
spool moves to the right, pump supply oil flows over the metering slots in the spool and into passage (16).
The hydraulic oil flows to the pressure compensator valve (6) and passage (26). In the pressure compensator valve,
the hydraulic oil flows into internal passages. The pressure compensator valve moves up. As the pressure compen-
sator 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 (16).
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 control the output
of the hydraulic pump. The hydraulic pump upstrokes and the hydraulic oil pressure in passage (16) increases.
When the hydraulic oil pressure in passage raises above circuit pressure, the hydraulic oil unseats load check valve
(19) and flows to passages (14 and 17).
In passage (14), the spool blocks the flow of the hydraulic oil. In passage (17), the hydraulic oil flows to passage
(18) and through port (2) to the work tool.
Hydraulic oil flows from the work tool to port (5). The hydraulic oil flows through the port to passage (13). The
hydraulic oil flows around spool (25) and into tank passage (8). The hydraulic oil flows to all control valves as
makeup oil. The hydraulic oil flows through an internal passage to back pressure check valve (1). When the pres-
sure overcomes the spring in the check valve, the check valve opens. The hydraulic oil flows through the check
valve to the tank.
When the operator releases the pilot valve, the flow of pilot oil to the pilot valve moves the shock reducing check
valve to the left. The hydraulic oil flows through an orifice. This dampens the flow of hydraulic oil to the pilot
valve. The spool slowly closes off the hydraulic oil to the circuit. Spring (9) moves spool (25) to the HOLD posi-
tion. Load check valve (19) blocks hydraulic oil in the hydraulic lines.