Hydraulics
9803/7130 Issue 1
7 - 4 7 - 4
Circuit Descriptions
Section E Section E
Component Key:
X Parallel Gallery
Y Service Line
4B Spool
4S Load Hold Check Valve
Excavator Valve - Load Hold Check Valves
Operation 1
Flow to the service via a typical solid spool 4B is controlled
by the load hold check valve 4S which is a spring-loaded
non-return valve operating across the pressure feed from the
parallel gallery X.The valve prevents reverse flow from the
rams into the pressure feed line, so maintaining ram
pressure until exceeded by system pressure. The illustration
shows a service selected but back pressure Y exceeds
system pressure which closes the load hold check valve 4S.
Operation 2
When pressure in the feed line exceeds back pressure, the
load check valve 4S opens and oil operates the ram. The
remaining load hold check valves are also opened by system
pressure but the galleries are dead-ended because the
spools are in neutral.
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