Pilot Check Valve; Crossover Relief Valve - Dodge D150 1990 Service Manual

• ACCESSORIES 1 - 3
PILOT CHECK VALVE
A p i l o t "check" valve is more sophisticated t h a n a
standard "check" valve because i t has a p i s t o n i n a d -
d i t i o n t o a b a l l "seat" a n d s p r i n g . A p i l o t "check"
valve i s located between solenoid-valve " C " a n d t h e
reservoir. I t has t w o functions:
• i t prevents t h e h y d r a u l i c fluid i n either a n g l i n g
c y l i n d e r from l e a k i n g back t o t h e reservoir; a n d
• i t allows t h e h y d r a u l i c fluid f r o m t h e r e t r a c t i n g
a n g l i n g cylinder ( d u r i n g a n a n g l i n g cycle) t o r e t u r n
to t h e reservoir.
T h e valve action i s accomplished b y pressurized h y -
d r a u l i c fluid m o v i n g t h e piston, w h i c h forces t h e
"check" b a l l off i t s "seat".
CROSSOVER RELIEF VALVE
T h e crossover r e l i e f valve has t h e function o f pro-
t e c t i n g against p o t e n t i a l damage t h a t can be caused
by a n abnormally h i g h opposite force (from impact)
being applied against t h e end of t h e blade (e.g., w h e n
t h e blade end contacts a curb or other immovable
structure). This type o f action w i l l cause very h i g h
h y d r a u l i c pressure t o accumulate i n one o f t h e a n -
g l i n g cylinders.
W h e n t h e h y d r a u l i c pressure increases sufficiently
to open t h e crossover r e l i e f valve, t h e valve allows
t h e h i g h l y pressurized h y d r a u l i c fluid t o flow directly
to t h e opposite power a n g l i n g cylinder. T h i s function
aids i n cushioning t h e impact a n d results i n only
changing t h e angle position o f the plow blade.
SYSTEM OPERATION
Refer t o Figures 2 t h r o u g h 5 for voltage application
a n d h y d r a u l i c fluid flow for each snow plow function.
Each figure i l l u s t r a t e s t h e components t h a t are actu-
ated and associated for t h e applicable function.