Service Manual User Manual

Section 9
9-64
9.9 VALVES AND MANIFOLDS
Valves are devices that open or close passageways.
Manifolds (derived from the words, “many folds”) contain
circuit passageways involved in the distribution of hydrau-
lic fluid flowing under pressure. There are various valves
and manifolds in use on this vehicle. As valves open and
close, hydraulic fluid is directed to flow through various
passageways to the prescribed circuit, causing vehicle
functions occur.
9.9.1 Unloader Valve
The unloader valve (Fig. 9–49 ) creates system pressure
and distributes the hydraulic fluid for various vehicle func-
tions via its load sense, bypass, primary, and auxiliary
supply ports.The unloader valve distributes fluid to the
hydraulic system oil cooler (Fig. 9–6) and is secured to
the underside of the frame near the transmission.
Figure 9–49. The unloader valve is secured to
the underside of the frame, located near the transmission.
DO NOT loosen, disassemble or attempt to adjust any of
the cartridges unless specifically instructed by Sky Trak
to do so! Tampering with the cartridges will irrevocably
alter pressure in the affected circuits. A new cartridge will
be required to rectify the situation.
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 NEUTRAL (N), engage
the park brake switch and shut the engine OFF.
2. Unlatch, unlock and open the engine cover. Allow the
hydraulic fluid to cool.
3. Label, disconnect and cap the hydraulic lines at the
unloader valve.
4. Remove the two 5/16-18 x 3-1/4" hex-head
capscrews, two 5/16" lockwashers and two 5/16"
SAE washers securing the unloader valve (Fig. 9–49)
to the vehicle frame. Remove the valve from the
vehicle. Wipe up any spilled hydraulic fluid.
b. Unloader Valve Disassembly
Safely secure the unloader valve (1, Fig. 9–50) in a
bench vise or by other suitable means. Remove the cap
(2), O-ring (3), spool spring (4), tube spacer (5), spool
(6), and relief valve assembly (8) from the unloader valve
housing (7). Discard the O-ring (3). Always replace O-
rings with new O-rings lubricated with clean hydraulic oil.
c. Cleaning and Drying
Clean metal parts in an approved solvent such as triclor-
ethylene and blow dry.
d. Inspection
Inspect all sealing surfaces. They must be clean, smooth,
and free of damage, and have no indication of wear.
Replace parts if damaged or worn.
e. Reassembly
Safely secure the unloader valve (1, Fig. 9–50) in a
bench vise or by other suitable means. Install the relief
valve assembly (8) and torque to 20 lb/ft (27 Nm). Install
the spool (6), tube spacer (5), spool spring (4), and new
O-ring (3). Always replace O-rings with new O-rings lubri-
cated with clean hydraulic oil. Thread the cap (2) tightly
into the unloader valve housing (7).
MS2020
WARNING: Hot hydraulic fluid can cause
severe burns. Wait for hydraulic fluid to cool
before servicing any hydraulic component.
WARNING: Escaping hydraulic fluid under
pressure can penetrate the skin, causing seri-
ous injury. Relieve hydraulic pressure before
servicing any hydraulic component.
Model 3606 • Origin 10/99