JLG 4394RT Service Manual - Manual (Page 186)

SECTION 4 - HYDRAULICS
4-20 – JLG Lift – 3121249
Pressure Setting Procedures
Cold temperatures have a significant impact on pressure
readings. JLG Industries Inc. recommends operating the
machine until the hydraulic system has warmed to normal
operating temperatures prior to checking pressures. JLG
Industries Inc. also recommends the use of a calibrated
gauge. Pressure readings are acceptable if they are within
± 5% of specified pressures.
1. Main Relief
a. Refer to Figure 4-16., Main Valve Block.
b. Locate the lift up solenoid valve. Remove the coil
nut and remove the coil from the cartridge. Do
not remove the wire out of the coil plug.
c. Install a pressure gauge, 3000 psi (207 bar) or
higher, at port MP1. Start the engine and activate
lift up.
d. Gauge should read 3000 psi (207 bar).
e. Adjust the main relief (RV2) clockwise to
increase, counter-clockwise to decrease.
f. Reintall the coil to the cartridge and torque to 5
lb-ft (6.8 Nm).
2. Lift Up Relief Valve
a. Refer to Figure 4-16., Main Valve Block.
b. Install a pressure gauge, 3000 psi (207 bar) or
higher, at port MP1. Start the engine and activate
lift up.
c. Gauge should read 2700 psi (186 bar).
d. Adjust the lift up relief (RV1) clockwise to
increase, counter-clockwise to decrease.
3. Steer Relief Valve
a. Refer to Figure 4-16., Main Valve Block.
b. Install a pressure gauge, 3000 psi (207 bar) or
higher, at port MS. Start the engine and activate
steer right or left.
c. Gauge should read 2500 psi (172 bar).
d. Adjust the steer relief (RV3) clockwise to
increase, counter-clockwise to decrease. This
relief valve takes care of both right and left.
4. Leveling Jack Retract Relief Valve
a. Refer to Figure 4-16., Main Valve Block.
b. Install a pressure gauge, 3000 psi (207 bar) or
higher, at port MP1. Start the engine and activate
jack retract.
c. When all jacks are retracted the gauge should
read 2500 psi(172 bar).
d. Adjust the relief valve located on the leveling
jack directional valve (refer to Figure 4-19.)
clockwise to increase, counter-clockwise to
decrease. (The relief valve is on the same face
as the solenoid valves).
5. Single Power Deck Relief Valve
a. Refer to Figure 4-20., Powerdeck Valve (Single).
b. A pressure gauge must be hosed in the power
deck retract circuit. Tee the gauge in port 2 of
the power deck valve.
c. Retract the power deck. Gauge should read
1500 psi (103 bar).
d. Adjust the relief valve (RV1) clockwise to
increase, counter-clockwise to decrease.
NOTE: This type of relief valve is a bi-directional type. Port 2
is the primary setting. Port 1 is the secondary set-
ting. Port 1 is a function of Port 2. When setting the
primary setting, the secondary setting can be as
much as 300 psi (21 bar) lower. In order to check
Port 1, tee in a gauge at Port 1.
6. Dual Power Deck Relief Valve
Front Power Deck:
a. Refer to Figure 4-21., Powerdeck Valve (Double).
b. A pressure gauge must be hosed in the power
deck retract circuit. Tee in a gauge at Port 4 of
the dual deck valve.
c. Retract the power deck. Gauge should read
1500 psi (103 bar).
d. Adjust the relief valves (RV1, RV2) clockwise to
increase, counter-clockwise to decrease.
NOTE: This type of relief valve is a bi-directional type. Port 4
is the primary setting. Port 3 is the secondary set-
ting. Port 3 is a function of Port 4. When setting the
primary setting, the secondary setting can be as
much as 300 psi (21 bar) lower. In order to check
Port 3, tee in a gauge at Port 3.
Rear Power Deck:
a. Refer to Figure 4-21., Powerdeck Valve (Double).
b. A pressure gauge must be hosed in the power
deck retract circuit. Tee in a gauge at Port 2 of
the dual deck valve.
c. Retract the power deck. Gauge should read
1500 psi (103 bar).
d. Adjust the relief valves (RV1, RV2) clockwise to
increase, counter-clockwise to decrease.
NOTE: This type of relief valve is a bi-directional type. Port 2
is the primary setting. Port 1 is the secondary set-
ting. Port 1 is a function of Port 2. When setting the
primary setting, the secondary setting can be as
much as 300 psi (21 bar) lower. In order to check
Port 1, tee in a gauge at Port 1.