jcb JS300 Service Manual page 706

Section E - Hydraulics
Hydraulic System
Hydraulic Operation and Schematics
Priority Valves
K Fig 12. ( T
For schematic, E-46).
Boom over Swing Priority (A)
This is selected by the operator via switch in the right hand
console.
When there is a boom up & swing pressure switch signal
the boom priority solenoid on the 8 spool block 60 is
energised sending a signal via port C6 to the main control
valve 14 at port Pi1. This selects the boom over swing
priority spool. Oil now being fed to the swing spool is
restricted to give priority to the boom.
Swing over Dipper Priority (B)
This is a non-selectable function automatically carried out
within the main control valve 14 when Swing is used.
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 from 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.
Boom Priority over Bucket (C)
This a non-selectable function automatically carried out
within the Main control valve 14 when Boom up is selected.
When boom up is selected a signal is sent from port C1 on
the servo shuttle valve 46 to the main control valve port
Pi2. This selects the boom over bucket priority valve C. Oil
now flowing to the bucket spool is restricted and gives
priority to boom up.
E-45 9813/5100-1 E-45