9803/3280
Issue 1
8 - 4
8 - 4
Circuit Descriptions
Section E
Section E
Component Key:
B
Parallel Gallery
D
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
B
. The valve prevents reverse flow from the
rams int o t he p ressure feed line, so maint aining ram
pressure until exceeded by system pressure. The illustration
shows a service selected but back pressure
D
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.