Valves And Manifolds; Unloader Valve - JLG sky trak mmv Service Manual

Hydraulic System
9.12

VALVES AND MANIFOLDS

Valves are devices that open or close passageways.
Manifolds contain circuit passageways involved in the
distribution of hydraulic fluid flowing under pressure.
There are various valves and manifolds in use on this ve-
hicle. As valves open and close, hydraulic fluid is directed
to flow through various passageways to the prescribed
circuit, causing vehicle functions to occur.
9.12.1

Unloader Valve

The unloader valve (1) creates system pressure and dis-
tributes the hydraulic fluid for various vehicle functions via
its load sense, bypass to tank (via the oil cooler), and pri-
mary and secondary valve ports. The unloader valve is
secured to the underside of the frame near the rear of the
hydraulic reservoir.
Front
1
DO NOT loosen, disassemble or attempt to adjust any
cartridges unless specifically instructed by JLG to do so!
Tampering with the cartridges will irrevocably alter pres-
sure in the affected circuits.
9.98
a. Unloader Valve Removal
1. Park the vehicle on a firm, level surface, fully retract
all hydraulic cylinders, ground the attachment (if
any), place the travel select lever in [N] NEUTRAL,
place the neutral lock lever in the [N] NEUTRAL
LOCK position, engage the park brake switch and
shut the engine OFF.
2. Place an Accident Prevention Tag on both the
ignition switch and the steering wheel, stating that
the vehicle should not be operated. Refer to Section
1.5, Accident Prevention Tag Usage .
WARNING:
cause severe burns. Wait for hydraulic fluid to
cool before servicing any hydraulic component.
3. Unlatch and open the engine cover. Allow the
hydraulic fluid to cool.
WARNING:
under pressure can penetrate the skin, causing
death or serious injury. Relieve hydraulic pres-
sure before servicing any hydraulic component.
4. At the unloader valve (1), label, disconnect and cap
the hydraulic lines (2). Remove the twelve capscrews
(3), twelve lockwashers (4), six flange halves (5) and
three o-rings (6).
5. Remove the three capscrews (7), lockwashers (8)
and washers (9) securing the unloader valve (1) to
the vehicle frame. Remove the valve from the
vehicle. Wipe up any hydraulic fluid spillage.
MT1770
1
8
7
Hot hydraulic fluid can
Escaping hydraulic fluid
6
5
9
4
3
Model MMV Rev. 12/04
2
2
MM4630