Loader Valve - Variable Flow
Loader Shovel Spool
The loader shovel spool operates in the same manner as the
auxiliary spool, refer to Auxiliary Spool.
The shovel valve section also houses auxiliary relief valves
(items 30 and 30A).
Under normal operating conditions, with the shovel in the
'carry' position, the mechanical linkage keeps the shovel
level as the arms are raised, to prevent spillage of the load.
If, as illustrated, the shovel is fully tipped when the arms are
being raised, the shovel is unable to tip further, producing
back pressure in the head side of the shovel rams and
cavitation in the rod side.
As the arms continue to rise, the back pressure increases
until it reaches the setting of A.R.V. 30A. This A.R.V. then
opens, allowing the excess back pressure to be dumped to
exhaust and prevent the rams and linkage from being
damaged.
The rod side A.R.V. 30 senses a higher pressure in the
exhaust gallery than in the service port and therefore opens
to allow exhaust oil to overcome the cavitation.
The shovel service may also be fitted with a ‘return to dig’
detent solenoid 12.
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