jcb JS300 Service Manual page 708

Swing Circuit
K Fig 13. ( T
For schematic,
Circuit description is for swing left.
Servo pressure from the hand controller 50 enters the
Servo shuttle valve 46 at port A2 and is distributed to:
1 Port C7 to port A on 8 station solenoid valve 60.
2 Port C8 to port Pc3 in main control valve to the Swing
over dipper priority spool SDV.
3 Port S1 to the Swing pressure switch 45.
4 Port B2 via the Swing shut off solenoid 44 to the
Swing spool at port Pa3 on the main control valve 14
to move spool across.
When the pressure switch 45 closes, a signal is sent from
the MECU to energise CT1 on the 8 station solenoid valve
60. This allows 40 bar (580 lb/in
then cross the shuttle CT10 and the Swing lock solenoid
CT3 to release the Swing brake.
When the Swing pressure switch 45 opens, the solenoid
remains energised for 5 seconds to allow the Swing to
come to a standstill before the brake is applied. If the
pressure switch fails, there is an override device fitted.
Servo pressure from the hand controller 50 passes
through the shuttle valve 46 and exits at C7. This signal is
sent to the 8 station solenoid valve 60 to port A, crosses
the shuttle CT10 and the Swing lock solenoid CT3 and
releases the Swing brake.
Note: When the override is in operation, the Swing may
become very harsh.
Flow from pump 2 travels through the neutral gallery to the
Swing spool. The flow is restricted allowing reduced
pressure at port ps1 which is sensed at pm2 of pump 2
allowing the pump to come to full flow. The flow passes
through into the parallel working passage to the Swing
spool. The flow is then directed via port A3 to the Swing
motor 1. Exhaust oil enters the main control valve 14 at B3
through the Swing spool to the tank line.
Swing over Dipper Priority (A)
This is a non-selectable function automatically carried out
within the main control valve 14 when Swing and dipper
are used together.
E-47
E-48).
2 ) to cross the solenoid
9813/5100-1
Section E - Hydraulics
Hydraulic Operation and Schematics
When Swing is selected a signal is sent from the servo
shuttle valve 46 via port C8 to the main control valve 14 at
port Pc3. This selects Swing over dipper priority valve B
and limits the flow to the dipper to at pump A1 only. This
makes it possible to have maximum Swing torque with
high Swing pressure when the dipper is used at the same
time.
Hydraulic System
E-47