Buick LeSabre 1965 Service Manual page 479

STEERING GEAR, STEERING COLUMNS AND LINKAGE POWER STEERING 8 - 1 5
pressure in the spring chamber
drops to a minimum value. Thus,
the pressure in the discharge
cavity also is reduced as this
pressure is governed by the
spring tension and the oil pres-
sure p r e s e n t in the spring
chamber of the pump.
If pump output pressure reaches
1100 to 1200 psi, the increased
pressure in the spring chamber
forces a pressure relief valve
open and oil escapes from the
spring chamber into the by-pass
hole around the pressure relief
valve ball. See Figure 8-21.
As oil pressure is relieved in the
spring chamber, the high pressure
in the pump discharge cavity
overcomes the spring load to open
the flow control valve. Because
outlet pressure has to pass
through an orifice to get into the
spring chamber, the pressure in
the spring chamber drops below
outlet pressure for a fraction of a
second. This allows the flow con-
trol valve to be open enough to
lower line pressure to a safe level
immediately. Oil is then pumped
into the by-pass passage until the
line pressure opposing the pump
drops below the relief valve set-
ting, permitting this valve to
close. The flow control valve then
resumes normal operation.
The flow control valve starts to
open at 300-400 RPM of pump and
is functioning when the pump is
running 465 RPM (400 RPM of en-
gine). The minimum flow a new
pump (46000, 48000 and 49000 Se-
ries) must produce is 1.75 gal.
per minute (or 1.25 for 45000
Series) at 465 pump RPM against
a pressure of 700 psi. The flow
plunger permits a maximum flow
of 2.3 gal. per minute at 1500
RPM against a pressure of 50 psi
on 45000 Series cars. A maxi-
mum flow of 2.8 gal. per minute
will be had on 46000, 48000 and
49000 Series cars. The pressure
relief valve is set for 1100 to
1200 psi.
The power steering pump identifi-
cation number is stamped on the
left side of the reservoir below
filler neck. The first 3 digits
show the day of the year (1
through 36 5) the pump was tested.
Next is a letter for manufacturer
identification (S for Sag in aw).
The last digit shows the year (5
for 1965, etc.).
A pressure hose connects the
pressure union in the pump to the
rotary valve in the steering gear
housing and a return hose con-
nects the rotary valve to the pump
reservoir.
8 - 1 0 OPERATION OF
POWER STEERING
GEAR
a. Neutral or Straight-Ahead
Figure 8-22 shows the rotary
valve in the neutral or straight-
/ Z ^ 0 ^ ^ ^ ^ \ P R E S S U R E
• 3
/ /-VALVE
I _ VALVE
RETURN
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SPOOL ^ ^ '
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BODY ^ ^
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RETURN
OIL ~~7
Figure 8-22—Oil Flow—Straight-Ahead