EP Equipment LIST JX0, Service Manual

Page: 92 / 206

79
REV. 07/2019
HYDRAULIC SYSTEM
7
7.5 Solenoid Valve
When solenoid valve coil is energized (there
is voltage between coil end A and B), the
electromagnetic coil generates electromagnetic
force, and the spool will move, the valve will
open, and the vehicle will be lowered.
When the contactor coil is de-energized, the
closing part will be released under the effect
of the released spring, the hydraulic oil cannot
form a loop, thus the lifting mechanism cannot
be lowered.
Spool
Electromagnetic Coil
7.5.1 Faults and Causes
1
Fault Solenoid valve does not work after
energized
Cause
a. Different power supply circuits;
b. Insufficient power supply
voltage;
c. Short circuit;
d. Unsoldering coil (coil short
circuit);
e. Main spool and moving core
of the solenoid valve blocked by
impurities;
f. High viscosity of hydraulic oil;
g. High frequency of use, service
life has expired already.
2
Fault Solenoid valve cannot be closed
Cause
a. Main spool or core seals broken
or aged;
b. Main spool and moving core
of the solenoid valve blocked by
impurities;
c. Spring deformation;
d. Balancing hole blocked by
impurities;
e. High frequency of use, service
life has expired already.
3
Fault Internal leakage
Cause Damaged seals or spring
deformations
4
Fault External leakage
Cause Loose connections or damaged
seals
5
Fault Noisy when energized
Cause
a. Unstable supply voltage;
b. Impurities on absorption surface
or uneven surface of core,
needs cleaning.
Checking
- Check the solenoid valve connector for loos-
ening or poor connection of leads.
7.5.2 Checking and Testing
Testing
-
-
Switch off the power supply of the vehicle;
Measure the resistance between solenoid
valve coil end point A and B to identify if the
coil is normal;
as shown in the following table:
- Check the solenoid valve for blocking:
the fitting clearance between slide valve
sleeve and spool is very small, when there
is impurity entering or too less lubricant, it is
easily blocked.
Resistance
Measurement
Judgment
Approx. 25 Ω Normal
0 Ω
Coil shorting
(replace the solenoid valve)
∞
Ω
Coil breaking
(replace the solenoid valve)
If the coil is normal, move on to the next step.
Handling method:
- Insert a steel wire from the small hole at va-
lve end to make the spool rebound;