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ACCESSORIES
•
SYSTEM DESCRIPTION AND OPERATION
HYDRAULIC
CYLINDER
AND MOTOR
The snow plow h y d r a u l i c cylinder a n d m o t o r (pow-
er) u n i t i s a n electrically powered, electrically con-
t r o l l e d
h y d r a u l i c mechanism
t h a t
is specifically
designed t o raise, lower and angle t h e blade.
The power u n i t is comprised o f a high, torque, 12-
v o l t motor t h a t is directly coupled t o a gear-type hy-
draulic p u m p . A driver-actuated, solenoid-controlled
switch located i n t h e engine c o m p a r t m e n t connects
battery voltage to t h e motor. T h e p u m p i s supplied
w i t h
h y d r a u l i c
fluid
f r o m a n i n t e g r a l
reservoir,
w h i c h completely surrounds t h e h y d r a u l i c cylinder
t h a t raises and lowers the blade.
The remotely located ( i n s t r u m e n t panel)
toggle
switches provide a means to electrically operate t h e
electro-hydraulic solenoid valves. T h e solenoid (elec-
tro-mechanical) h y d r a u l i c valves
(designated " A " ,
" B " , and "C"), along w i t h t h e mechanical h y d r a u l i c
check valves, p i l o t check valve a n d crossover r e l i e f
valve, control t h e pressurized h y d r a u l i c f l u i d for
snow plow blade positioning.
SOLENOID
(ELECTRO-MECHANICAL)
VALVES
Three
solenoid
(electro-mechanical)
h y d r a u l i c
valves are used for snow plow h y d r a u l i c f l u i d control.
Each solenoid valve is comprised o f t w o components:
• cartridge — comprised of a valve and a solenoid
armature t h a t enables the h y d r a u l i c valve t o be op-
erated a n d controlled electrically; a n d
• coil — t h e electrical component t h a t retracts t h e
cartridge
solenoid
a r m a t u r e
( a n d t h e h y d r a u l i c
valve) v i a electromagnetic action.
T h e c a r t r i d g e t h r e a d s into a n d o u t o f the
p o w e r u n i t s i m i l a r to the w a y a s p a r k p l u g i s i n -
stalled a n d r e m o v e d from a n engine.
W i t h power applied, t h e solenoid a r m a t u r e (con-
nected t o the h y d r a u l i c valve) retracts and p u l l s the
spool or poppet valve i n t o the O P E N position.
When t h e current flow ceases (power off), t h e com-
pressed coil spring forces the a r m a t u r e (and t h e hy-
draulic
valve) back
t o i t s n o r m a l ,
de-energized
CLOSED position.
SOLENOID VALVE "A"
The solenoid valve " A " cartridge contains a poppet
valve t h a t is n o r m a l l y de-energized i n t h e C L O S E D
position. W h e n closed, t h e valve r e t a i n s pressurized
hydraulic f l u i d i n the l i f t cylinder. W h e n i t is ener-
gized (valve opened), i t allows t h e h y d r a u l i c f l u i d to
flow from t h e l i f t cylinder back t o t h e reservoir,
w h i c h enables the plow blade t o lower v i a g r a v i t y .
Solenoid valve " A " is designed t o r e m a i n energized
(valve open) d u r i n g snow plow operation t o provide a
" f l o a t i n g " blade position, w h i c h ensures t h a t t h e
plow blade is guided up-down b y t h e surface devia-
tions.
SOLENOID VALVE "B"
The solenoid valve " B " cartridge contains a spool
valve t h a t i s n o r m a l l y i n t h e de-energized
CLOSED
position t o allow t h e pressurized h y d r a u l i c f l u i d to
flow t o solenoid valve " C " . I n t h e energized O P E N
position, t h e pressurized h y d r a u l i c f l u i d is diverted to
the l i f t cylinder, w h i c h causes t h e plow blade to be
raised.
SOLENOID VALVE "C"
The solenoid valve " C " cartridge contains a spool
valve t h a t i s n o r m a l l y i n t h e de-energized
CLOSED
position t o allow t h e pressurized h y d r a u l i c f l u i d to
flow to t h e right-side power a n g l i n g cylinder, w h i c h
angles t h e plow blade t o t h e left. A t t h e same t i m e ,
i t allows t h e h y d r a u l i c f l u i d t h a t is being forced from
the r e t r a c t i n g left-side power a n g l i n g cylinder to flow
t h r o u g h t h e " C " cartridge valve and r e t u r n t o t h e
pump reservoir.
E n e r g i z i n g t h e solenoid valve w i l l route pressur-
ized h y d r a u l i c f l u i d to t h e left-side a n g l i n g cylinder,
w h i c h angles the plow blade t o the r i g h t . Also, dur-
i n g t h i s action, the h y d r a u l i c f l u i d is forced from the
r e t r a c t i n g right-side power a n g l i n g cylinder, i t flows
t h r o u g h t h e " C " cartridge valve and i t r e t u r n s to the
pump reservoir.
MECHANICAL
HYDRAULIC
VALVES
The mechanical h y d r a u l i c valves a l l have the same
function: t h e y control t h e d i r e c t i o n o f the hydraulic
f l u i d flow.
CHECK VALVES
H y d r a u l i c "check" (one-way) valves allow f l u i d to
flow freely i n one direction w h i l e preventing f l u i d
from f l o w i n g i n the opposite direction.
A p u m p "check" valve is used i n a l l applications to
prevent h y d r a u l i c f l u i d f r o m l e a k i n g back t h r o u g h
the p u m p t o the reservoir.
Two a d d i t i o n a l "check" valves are necessary be-
cause solenoid valves " B " a n d " C " (as do a l l spool
valves) have some leakage.
One
"check" valve
is located between
solenoid
valve " B " and t h e l i f t cylinder. I t prevents f l u i d i n
the l i f t cylinder from l e a k i n g back t h r o u g h solenoid
valve " B " , w h i c h could cause the w e i g h t of the plow
to angle t h e plow blade to t h e left by forcing f l u i d
t h r o u g h solenoid valve " C " i n t o t h e right-side power
a n g l i n g cylinder.
The other "check" valve is located between solenoid
valve " B " and solenoid valve " C " . I t prevents the hy-
draulic f l u i d i n either power a n g l i n g cylinder from
being forced t h r o u g h solenoid valve " B " and back to
the l i f t cylinder.
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