THEORY OF OPERATION - CONTINUED
HYDRAULIC SYSTEM - CONTINUED
When a single hydraulic circuit is activated from the HOLD position and a pump STANDBY position, the spool
shifts due to pilot oil from the pilot lever. Pump supply oil flows over the metering slots on the spool to passage
(18). The hydraulic oil in passage flows to the pressure compensator valve (6).
When the hydraulic oil pressure increases, 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 is signal oil. Spring
and the signal oil balance the hydraulic oil pressure in passage (18). This controls the flow of hydraulic oil across
If this circuit has the highest hydraulic oil pressure in the main control valve, 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 compensa-
tor valve on the hydraulic pump in order to signal the pump. The hydraulic pump upstrokes and the hydraulic oil
pressure in passage (18) increases. When the hydraulic oil pressure in passage raises above circuit pressure, the
hydraulic oil unseats load check valve (21) and flows to passages (15 and 19).
More than one hydraulic circuit can be activated at a time. The highest signal oil pressure is sensed through pas-
sage (4) to the chamber and spring (3) above each pressure compensator valve. The hydraulic circuit with the high-
est hydraulic oil pressure controls the operating pressure differential between passages (18 and 19). The signal oil
pressure and the circuit pressure will match.
The same signal oil pressure will act on each pressure compensator valve. The pressure differential across each
activated spool will match. The hydraulic pump will attempt to meet all flow demands. If the pump cannot meet all
flow demands, the flow across each spool will be reduced proportionally.