Subaru 2002 Impreza Service Manual page 338

PROPORTIONING VALVE
Brakes
2) Operation at the split point pressure
When pressure
"P2"
increases to the split point pressure, force
"f2"
is generated. (Piston's cross
sectional area "A" has been selected so that the force is generated starting with the split point pres-
sure.) The pressure pushes the piston rightward, overcoming spring force "F". As a result, the pis-
ton moves rightward and comes in contact with the lip seal, blocking the passage toward the rear
wheel cylinders.
(1) To rear wheel cylinder
(2) From master cylinder
(3) Lip seal
I
F A
I
f2
NF0251
(4)
Spring
(5) Piston
3) Operation after reaching the split point pressure
Immediately before the fluid passage toward the rear wheel cylinders is closed, pressure "P2" is
slightly higher than pressure
"P3".
So the piston can move in the spring force acting direction and
the fluid can flow to the wheel cylinders. However, as soon as pressure 'iP2" becomes equal to liP3",
the passage closes.
This cycle is repeated as long as the pedal is depressed further, but pressure increasing rate of
the rear wheel cylinders is smaller than that of the front wheel cylinders.
BR-I 2