Control Valve - Boom Spool Shifted - New Holland LS140 Workshop Manual

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CONTROL VALVE - BOOM SPOOL
SHIFTED
Boom Control Operation
Foot Controls
When the toe of the control pedal is pushed down, it
will shift the control valve spool in, lowering the boom.
When the heel of the control pedal is pushed down it
will shift the control valve spool out, raising the boom.
Hand Controls
When the left control handle is pivoted down, it will
shift the control valve spool in, lowering the boom.
When the left control handle is pivoted up, it will shift
the control valve spool out, raising the boom.
1. Oil flows from the gear pump, 1, through pres-
sure line, 2, to control valve, 3.
2. When the boom valve spool, 4, is pulled out, the
oil flows from the rear work port, 5, to the base
(piston) end of the boom cylinder raising the
boom.
SECTION 35 - HYDRAULIC SYSTEM
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35-24
3. When the boom valve spool, 4, is pushed in, the
oil flows from the front port, 6, to the shaft end of
boom cylinders, to lower the boom.
4. When the boom circuit is operated to maximum
pressure or cylinders are bottomed, the main
system relief valve will relieve the high pressure
oil into the return oil valley in the control valve, re-
turning the oil to the reservoir.
5. The return oil from the opposite side of cylinders
being pressured will return through the control
valve to the reservoir.
6. When the boom cylinders are extended, the
boom control valve spool is in neutral, and a load
is put on the boom cylinders causing them to re-
tract the circuit. Relief valve, 7, will relieve the
pressure in the base (piston) side of cylinders
protecting the cylinder and lines. The oil relieved
from the circuit relief valve enters the return oil
galley in the control valve and returns to the res-
ervoir.
7. When the boom valve spool, 4, is pushed in all
the way, it will put the spool into detent position,
holding the spool, opening both work ports 5 and
6 to the return allowing the boom to float.
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