JLG GRADALL 522 Owner'S/Operator'S Manual Download

Page: 61 / 288

79.37

3.125

36.32

1.43

64.00

2.52

32.00

1.26

50.8

2.07

19.05

.75

86.86

3.42

43.43

1.71

61.91

2.43

136.12

5.35

369.87

14.56

22.22

.875

38.10

1.50

PRESSURE PORT

FLOW
THRU
PORT

BRAKE
PORT

RETURN PORT

millimeters

nches

NOTE: Dimensions will vary

slightly between units
and are to be used for
reference purposes only.

FIGURE 6

DIA. THRU
(3) HOLE

- 20 UNF - 28 THD.

2 13

DEEP

one-half the brake line pressure, the
PRESSURE REGULATING SPOOL
shifts a minute amount and the
pressure is regulated across LAND
“A” and LAND “B” (Figure 4).
If the pressure required by the
brake valve is lower than that
required by the power steering, the
power steering will not normally
interfere with the operation of the
brake (Figure 4).
NOTE:

is equal to one-half of the brake line
pressure.  To accomplish this, the
area of the MASTER CYLINDER
PISTON is twice the area of the
MASTER CYLINDER.  Therefore,
any pressure that is applied to the
MASTER CYLINDER PISTON will
be multiplied by two to determine the
master cylinder pressure.  The
pressure regulating spring can be
factory set to normally limit brake
line pressure regardless of system
pressure.
This valve will act as a manual
brake master cylinder, in the event
of failure in the hydraulic circuit
supplying power to it.   The
PRESSURE REGULATING
SLEEVE contacts the MANUAL
BRAKE ACTUATING SLEEVE
which, in turn, pushes directly on the
master cylinder piston, thereby
building pressure in the MASTER
CYLINDER (Figure 5). This requires

a longer stroke in the pedal.  This
amount of pressure that can be
generated in the brake lines in
manual operation is proportional to
the pedal ratio and the effort which
the operator is able to exert on the
pedal. In most cases, the operator
is not able to build as much pressure
in the brake line as can be done in
power operations.  The ports from
the pump are restricted when the
valve is actuated manually; however,
as soon as the engine is started,
hydraulic pressure will push the
MANUAL BRAKE ACTUATING
SLEEVE back against the retaining
ring which contains it and the valve
again functions with power.  This is
rather an abrupt action when the
engine is started, causing the brake
pedal to return to its power mode
position, and it is suggested that the
brakes not be applied manually when
starting the engine.

INSTALLATION INSTRUCTIONS

Mount MICO Open Center Power
Brake Valve on vehicle and
complete push rod and pedal hook-
up. NOTE: It is important that the
system reservoir be mounted above
the brake valve, or that the return
line have a vertical section of one
foot directly above the valve.
The pedal assembly must have its
own return spring. DO NOT rely on

the internal spring in the valve for
this function.
Pedal should be adjusted to allow
1/32” clearance between pressure
regulating rod and actuator.
Bleed system (see bleeding
instruction on page 14).
Be sure all hydraulic fittings are tight
and visually check system for leaks
with power applied.

Brake line pressure can
exceed preset specifica-
tions in the unusual condi-
tion of a simultaneous
brake application and sud-
den elevation of the steer-
ing pressure above the
value.

In the standard MICO Open
Center Valve, the pressure in the
REACTION CHAMBER and ahead
of the MASTER CYLINDER PISTON

(5)

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