NMC-WOLLARD MB-4 200-DF, Operation, Maintenance And Parts Manual

Page: 58 / 321

below relates the precharge temperature
(T
o
) to the operating temperature (T).
Fahrenheit
P
O
,T
O
=P
O
,T
2
x(T
O
+460)/(T
2
+460)
T
O
=precharge temperature
T
2
=maximum operating temperature
P
O
,T
O
=gas precharge pressure at precharge
temperature
P
O
,T
2
=gas precharge pressure at maximum
operating temperature
NOTE: Substitute 273 for 460 in above for-
mulas for Celsius calculation.
3.10.2 OPERATING AND INSTALLATION
INSTRUCTION
Preparation
To check the gas precharge pressure in an
accumulator, it must first be isolated from the
system shut off, and all hydraulic pressure
relieved.
For accumulators with HYDAC gas valve
version 4, unscrew the valve protection cap
“H” (where applicable) and the valve seal
cap ‘G” (see fig. 5).
FPS Unit
Prior to connecting the charging and gauging
unit to an accumulator, turn T-handle “A”
counter clockwise until resistance is felt.
Close manual bleed valve ‘B” by hand tight-
ening. Connect the unit to the accumulator
by screwing cap nut “D” onto HYDAC gas
valve version 4; hand tighten (see fig 5).
Checking Gas Precharge Pressure
Connect the appropriate charging and gaug-
ing unit to the accumulator following the in-
structions under “Preparation”, following.
NOTE: Temperature affects the gas
precharge pressure, please refer to previ-
ous “Temperature Effect” instructions.
FPS Unit
Turn T-handle “A” clockwise a maximum of
3 full turns from the full counterclockwise
position. The gauge needle should indicate
the existing gas precharge pressure. If
there is no gas precharge pressure indi-
cated or if it is too low or too high, please
follow instructions under the appropriate
section, either “Pressure Release’ or
“Charging” . If desired gas precharge pres-
sure registers, please follow the instruc-
tions under ‘Removal of Charging and
Gauging Unit”.
Pressure Release
With the appropriate charging and gauging
unit attached as previously described, gas
precharge pressure can be released by
carefully opening manual bleed valve “B”.
Release the gas precharge pressure very
slowly until the desired gas precharge
pressure is reached (this insures that the
gas temperature does not fluctuate greatly,
providing and accurate gas precharge
pressure). Close the manual bleed valve
‘B”. Allow the gas precharge pressure to
stabilize. (5 to 10 minutes) recheck, adjust
if required. Once the desired gas
precharge pressure is reached, please fol-
low the instructions under “Removal of
Charging and Gauging Unit”.
Charging
Never use oxygen or
air, this could cause an explosion. Use
dry nitrogen or other recommended
gases.
PAGE 3-12 PREVENTIVE MAINTENANCE
JULY 31, 2007
M200 MB4 Tow Tractor Manual No. 42975