Operation and maintenance manual

Section 220-0100
4
Steering System - Flow Amplifier Valve
SM 1392 Rev 3 10-03
RL
7
PT
LS
CR
CL
8
8
R
5
EF P PP HP LS HT T L
A
TANKSUPPLY FROM
MAIN HYDRAULIC
PUMP
LEFT HAND
CYLINDER
RIGHT HAND
CYLINDER
SM - 6666B
In this condition, the body control valve has priority
over the steering valve. If oil is not required to operate
the body hoist cylinders, the oil flows through the body
control valve and back to tank.
Right Hand Turn
Numbers in parentheses refer to Figs. 1 & 6. Refer to
Fig. 4 for hydraulic schematic of the flow amplifier valve
and steering valve operating in the right turn position.
On turning the steering wheel for a right turn
application, oil flows from the steering valve 'LS' port to
the flow amplifier valve 'LS' port. The oil flows through
the load sensing orifice and into the spring cavity of
priority spool (7) moving the spool to the left. This
movement allows oil to flow out of port 'P' in the flow
amplifier valve and into port 'P' in the steering valve.
Oil leaves the steering valve through port 'R' and into
the left hand end of directional spool (6). This pressure
moves directional spool (6) to the right allowing a pilot
pressure to act on the right hand end of amplifier spool
(8). Pilot pressure overcomes spring pressure on the
left hand end of amplifier spool (8) moving amplifier
spool (8) to the left. This movement allows the main oil
flow from priority spool (7) and pilot flow through
directional spool (6) to merge at directional spool (6)
and flow through port 'CR' to the steering cylinders.
Return oil from the opposite ends of the steering
cylinders flows into port 'CL' and through directional
spool (6). Oil then flows through counter pressure &
anti-cavitation valve (2) and back to tank.
In this condition remaining oil supplied from the main
hydraulic pump, is available for the body hydraulics or
is returned to tank.
Left Hand Turn
Numbers in parentheses refer to Figs. 1 & 6. Refer to
Fig. 5 for hydraulic schematic of the flow amplifier valve
and steering valve operating in the left turn position.
On turning the steering wheel for a left turn application, oil
flows from the steering valve 'LS' port to the flow amplifier
valve 'LS' port. The oil flows through the load sensing
orifice and into the spring cavity of priority spool (7)
moving the spool to the left. This movement allows oil to
flow out of port 'P', in the flow amplifier valve, and into port
'P' in the steering valve.
Oil leaves the steering valve through port 'L' and into
Fig. 4 - Hydraulic Schematic - Right Turn
5 - Flow Amplifier Valve
7 - Steering Valve
8 - Steering Cylinders