jcb JS300 Service Manual page 180

Operation
Operating Levers/Pedals
Rockbreaker Circuit
This system supplies a one-way, regulated hydraulic flow to operate a rockbreaker. The flow to the rockbreaker
is controlled by a pedal at the operator's feet. Automatic engine speed reduction is incorporated, to prevent
damage to the rockbreaker because of excessive oil flow.
Two-Way Auxiliary Circuit
This system supplies a two-way flow, controlled by the pedal. It is suitable for attachments which need a
relatively high flow in either direction.
Combined Rockbreaker and Two-Way Auxiliary Circuit
This system allows the operation of a rockbreaker and two-way attachments without changing the pipework.
Rockbreaker, Two-Way Auxiliary and Merged Flow System
This system allows the operation of a rockbreaker and standard flow two-way attachments. The outputs of both
pumps can be merged to give a greater flow for high capacity attachments such as large demolition cutters
and crushers.
Low Flow Auxiliary Circuit
This system lets the joystick operate a low flow attachment (for example a weedcutter).
Change-Over Valves
To change from the bucket to the grab option operate the change-over valve.
Figure 136.
A
A Change-over valve
If you operate the change-over valve with stored pressure in the hydraulic system its seals will be damaged.
When the change-over valve is operated, you must follow the procedure below to prevent damage to its seals.
Remove the handle from the change-over valve when the machine is in use, to prevent the accidental operation
of the change-over valve.
Bucket Mode to Grab Mode
1. Fully retract the bucket ram, extend the arm and lower the boom to the ground.
2. Extend the bucket ram until the bucket sits flat on the ground.
3. Set the engine speed to minimum.
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