JLG 1250AJP Service Manual - Manual (Page 415)

SECTION 5 - HYDRAULICS
3121171 – JLG Lift – 5-61
NOTE: Shim thickness 1 mm = 56 psi (3.86 bar). Shims are
available in 0.3, 0.5, and 1.0 mm thickness.
Mechanical Centering of Pump
PREPARATION FOR ADJUSTMENT
The control piston has strong centering springs to ensure
that once the pump is adjusted for the neutral position it
will always return to neutral. If an adjustment is necessary
follow the steps listed below.
To ensure there is equal pressure on both sides of the
control module during the centering operation, it is neces-
sary to connect the X
1
and X
2
ports together by means of
hose or tubing. (No less than a 1/4 inch ID) The port sizes
are:
With pressure gages installed at M
A
, and M
B
, and with A
and B ports blocked (or motor stalled), and with the pump
running, loosen the jam nut. Turn the mechanical center-
ing adjusting screw until 1000 psi is read on M
A
, or M
B
then turn screw opposite direction until 1000 psi is read
on other pressure port. Turn the screw back, splitting the
distance between the previous two positions. This should
be the neutral position. Pressure on M
A
, and M
B
should
be equal.
Tighten jam nut, stop the pump drive, remove the hose
connecting ports X
1
and X
2
.
Hydraulic Centering of Control Modules
PREPARATION FOR ADJUSTMENT
When control modules are exchanged or replaced, it is
generally necessary to center the new module. This is
done by running the pump with gauges installed at ports
X
1
, X
2
, M
A
, and M
B
Release the jam nut and turn the
adjustment screw on top of the control module valve
body.
The adjustment screw is an eccentric, therefore, turning
more than 90’ in either direction will have no further cen-
tering effect, and could cause damage to the eccentric
pin.
CENTERING THE EP CONTROL MODULE
With no electrical signal to solenoids A and B, (remove
both plug-in connectors), the EP control module is cor-
rectly adjusted when any or all of the following conditions
exist:
1. Approximately, when equal control pressures are
obtained at control pressure ports X
1
and X
2
.
2. The hydraulic motor does not turn when the brake is
released.
3. Charge pressure is registered equally at ports M
A
and M
B
, when the flow output of the pump is dead-
headed against a locked motor or a valve.
If difficulties are encountered in obtaining neutral position
of the HD or EP control modules, check that the ends of
Pump Size Allen Wrench Wrench
28 5 mm 17 mm
Pump Size Tool Required Wrench
28 Screwdriver 10 mm