jcb JS300 Service Manual page 690

Section E - Hydraulics
Hydraulic System
Hydraulic Operation and Schematics
Linear Travel Valve Spools Operation
If another service (boom up for example) is selected at the
same time as straight line travel, there would be a flow
difference at the LH and RH track motors. This would
cause the machine to track to one side even though both
travel spools are fully selected. The linear travel valve
spools prevent this happening.
To demonstrate the linear travel, both travel spools and
boom up spool have been selected, refer to individual
circuits.
K Fig 4. ( T E-30)
Servo pressure enters the main control valve 14 at Pa1 to
select LH travel spool. This pressure is seen at the travel
pressure switch 52 and also selects the linear travel spool
(LT1)
Servo pressure enters main control valve 14 at Pa6 to
select RH travel spool. The pressure is also seen at the
travel pressure switch 52 and also selects the linear travel
spool (LT2)
Servo pressure has entered the main control valve 14 at
Pa8 to select the boom up spool. This pressure is also
seen at the inlet port of linear travel spool LT1 and passes
through LT2 to select liner travel spool (LT3)
Oil from pump 2 enters the main control valve 14 at port P2
and is used at the boom 1 spool. This also passes over the
selected LT3 spool to supply the boom 2 spool. The oil
from both boom spools 1 and 2 merges and exits the main
control valve 14 at A8 to raise the boom via boom rams 13.
Oil from pump 1 enters the main control valve 14 at port P1
and is available at the LH travel spool and the RH travel
spool via LT3. Since the LH and RH track motors 5L and
5R are connected directly to the same pump they both run
at the same speed, maintaining straight line travel.
E-29 9813/5100-1 E-29