jcb JS300 Service Manual page 688

Section E - Hydraulics
Hydraulic System
Hydraulic Operation and Schematics
Neutral Circuit
K Fig 3. ( T
For Schematic, E-28).
With all the controls in the neutral position, flow from pump
1 enters the main control valve 14 at port P2 and flow from
pump 2 enters the main control valve 14 at port P1.
Oil is allowed to flow across all of the spools via the neutral
gallery when all controls are in the neutral position. Oil from
pump 1 exits port Ps2 and oil from pump 2, exits port Ps1
at the top of the main control valve.
Both flows of oil meet a separate restrictor and relief valve.
Some oil will pass through the restrictor above 40 bar and
back to tank, creating back pressure in the line. Oil is
exhausted across the negative controls relief valves at 40
2
bar (580 Ib in ). The back pressure created is sent to ports
Pi1 and Pi2 negative control ports on the pumps to keep
the pumps at minimum flow.
Load Assist Valve Operation
The load assist valve 15 is connected in circuit with the
negative control line of pump 2. Under normal conditions it
allows free flow of the control signal to pass to pump 2 from
Ps2 on the main control valve.
The solenoid 9 will automatically energise if the exhaust
gas temperature criteria during regeneration of the Diesel
Particulate Diffuser (DPD) is not met.
For more information about the load assist valve refer to
Section C - Engine and Power Control - Engine
Exhaust After Treatment.
E-27 9813/5100-1 E-27