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Operation
Functional Description
The HZ, HA, HB, and HE controls consist of a ported housing mounted directly to the end cap. Variable
signal pressure fed to port X1 is routed to the end of the 4-way valve. A threshold spring and ramp
spring(s) act on the opposite end of the 4-way valve.
HZ Control
The HZ control has a check valve to resolve which port (system A or B) is higher pressure. It routes this
high pressure to the 4-way valve to power the servo piston.
HA and HB Controls
The HA and HB controls have internal porting to feed system A or B pressures, respectively, to the 4-way
valve to power the servo piston.
HE Control
The HE control has no internal porting for servo supply pressure. An external servo supply pressure fed to
port M5 is required.
HZ Schematic Diagram
T2
T1
B
A
T7
max.
disp.
L2
M4
M3
M2
M5
T8
T3
L1
M1
M7
X1
P107 823
Service Manual
Series 51 Hydraulic Proportional Controls Service Manual
HZ, HA, HB, HE Controls
18
11009446 • Rev BA • July 2014