Operation
Functional Description
JA control is a stand-alone, dual signal hydraulic proportional control. The control housing contains a
pressure compensating override (PCOR) valve, a brake pressure defeat (BPD) valve, and passages to route
oil to the 4-way valve and to the servo piston ends. An external servo supply pressure fed to port M5 is
required. A threshold spring and ramp spring(s) act on the opposite end of the 4-way valve.
Signal Pressure
Separate external variable signal pressures are fed into ports XA or XB. The BPD spool resolves which
signal pressure is higher and routes this signal pressure to the end of the 4-way valve. The signal pressure
shifts the 4-way valve and it ports servo supply pressure to the ends of the servo piston, changing motor
displacement in proportion to the signal pressure.
JA Control Schematic Diagram
n
T2
T3
T7 T8
T1
T6
T4
max.
disp.
B
XB
XA
A
L2
M4
M3
N
M1
L1
M2
(M5)
X3
P106 420E
U7
Loop flush
PCOR
BPD
Repair
Disassembly
1. Remove PCOR lock nut (M14).
2. Remove and discard O-ring (M16).
3. Remove adjuster ( Z*).
4. Remove spring (M18).
5. Remove spool assembly (M20).
C
Caution
Do not remove PCOR valve bushing (M21).
Service Manual
Series 51 Hydraulic Proportional Controls Service Manual
JA Control
36
11009446 • Rev BA • July 2014