Allied Systems Allied H6G Series, Service Manual

Page: 23 / 122

Section 1
1 - 15
Figure 1-17 Hydraulic System - LINE-OUT
Sequence of Operation, Rescue Winch - LINE-OUT
The operator pushes the control lever forward, which
sends pilot control pressure to the direction control valve
and the brake release valve. Oil fl ows from the pump
supply line into the direction control spool cartridge and
continues to the inlet B port of the hydraulic motor. Pres-
sure builds from resistance against the counterbalance
valve, as well as mechanical and volumetric resistance.
This pressure supply communicates through a check valve
to pilot the counterbalance valve open until the inlet pres-
sure falls below a set value, and the counterbalance valve
closes. Similarly, the same pressure is communicated
to the tractor pump load sense controller and the pump
displacement is increased or decreased depending on
the load induced pressure. Oil fl ows through the motor
back through the direction control spool and to the trac-
tor reservoir. Simultaneously, pilot control pressure at the
brake valve is connected to the brake release port, and the brake is fully released. Low pressure case drain oil fl ows
from the hydraulic motor back to the tractor reservoir. This
condition drives the winch drum in
LINE-OUT .
When the winch is operated in LINE-OUT and a load
pulls line from the winch pressure builds on the A port
of the motor up to the load sense relief setting. When
pressure on the A port of the motor exceeds 3500 psi,
the load sense relief valve opens. The load sense pres-
sure signal decreases, and the tractor pump strokes back
reducing displacement so pressure at the hydraulic motor
decreases a corresponding amount. If pressure on the
inlet B side of the hydraulic motor drops below the pilot
setting of the counterbalance valve, the counterbalance
valve closes and acts as a relief valve on the A port of the
hydraulic motor. The valve relieves when pressure on the
A port reaches 4500 psi.