Operation and maintenance manual

Section 220-0100
3
SM 1392 Rev 3 10-03
RL
7
PT
LS
R
5
EF P PP HP LS HT T L
A
TANKSUPPLY FROM
MAIN HYDRAULIC
PUMP
Steering System - Flow Amplifier Valve
OPERATION
Neutral Position
Numbers in parentheses refer to Figs. 1 & 6. Refer to
Fig. 3 for hydraulic schematic of the flow amplifier
valve and steering valve operating in the neutral position.
Oil flows out of the hydraulic tank, through the main
hydraulic pump, through check valves and enters the
flow amplifier valve at port 'HP'. Oil flows through
priority spool (7) and dead heads at amplifier spool (8).
At the same time, oil flows through priority spool (7),
exits from port 'P' and flows into the steering valve at
port 'P'. This pressure is dead headed at the steering
valve and, as the pressure builds up, pilot pressure is
tapped off of line 'P' and flows through port 'PP' to the
left hand end of priority spool (7).
This pressure moves priority spool (7) to the right,
thus opening the main supply 'HP' line to the 'EF'
passage. Oil exits from port 'EF' to the inlet port 'P'
on the body control valve. At the same time, a
restricted pressure in line 'P' maintains the pilot
pressure on the left hand end of priority spool (7).
SM - 6666A
Fig. 3 - Hydraulic Schematic - Neutral Position
Orifice (3) meters oil in the left hand end of amplifier
spool (8). During right or left hand turns this oil will
balance amplifier spool (8).
Orifice (4) meters working pressure in the load
sensing line 'LS' during normal steering operation and
dead heads at system relief valve (1).
Check valve (9) is located in the right hand end of
amplifier spool (8).
Orifices (10) are threaded into the ends of directional
spool (6). Their purpose is to control the movement
of directional spool (6) which controls the oil flow to
the steering cylinders.
Throttle check valve (11) is located in pilot pressure
port 'PP'.
Orifice (12) is threaded in the cross passage above
amplifier spool (8) and meters oil in the right hand
end of amplifier spool return spring area.
Orifice drillings are located in covers (13 & 14) at
either end of directional spool (6).
5 - Flow Amplifier Valve
7 - Steering Valve
8 - Steering Cylinders