Lull 944E-42 Service Manual - Manual (Page 150)

Hydraulic System
8-34 944E-42
8.7.15 General Information
Each accumulator (1) is a 3,000 psi (207 bar) diaphragm
type accumulator. Each accumulator has a total volume
of 1.06 qt. (1 liter) (gas & oil combined).
The pneumatic accumulator is operated by compressed
gas. Gas and hydraulic oil occupy the same container.
When oil pressure rises, incoming oil compresses the
gas. When oil pressure drops, the gas expands, forcing
the oil out into the service brake system.
The gas is separated from the oil by a flexible diaphragm.
This diaphragm prevents the mixing of gas and oil and
keeps the gas out of the hydraulic system.
The accumulator must be “pre-charged” with gas before
use in the service brake system. This is done by filling the
gas chamber with dry nitrogen to a pressure of
450 ± 35 psi (3103 ± 241 kPa). The gas valve (2) is
located under the protective cap (3) at the top of the
accumulator. The gas valve is used for pre-charging and
testing the accumulator.
e. Pre-Charging the Accumulator
Note: Replacement accumulators are not pre-charged
when shipped.
Pre-charge accumulators with nitrogen gas only.
Nitrogen gas is free of water vapor and oxygen which
makes it harmless to internal parts and will not react if
mixed with oil under pressure.
Pre-charge Pressure/Temperature Range
Operating
Temperature
Actual Pre-charge Pressure
30°F (-1° C) 414 psi (2854 kPa)
40°F (4° C) 423 psi (2916 kPa)
50°F (10° C) 432 psi (2978 kPa)
60°F (16° C) 441 psi (3040 kPa)
70°F (21° C) 450 psi (3103 kPa)
80°F (27° C) 459 psi (3165 kPa)
90°F (32° C) 468 psi (3227 kPa)
100°F (38° C) 477 psi (3289 kPa)
110°F (43° C) 486 psi (3351 kPa)
120°F (49° C) 490 psi (3378 kPa)
130°F (54° C) 499 psi (3440 kPa)
140°F (60° C) 508 psi (3503kPa)
150°F (66° C) 517 psi (3565 kPa)
160°F (71° C) 526 psi (3627 kPa)
MU1941
1
WARNING
NEVER fill an accumulator with oxygen! An
explosion could result if oil and oxygen mix under
pressure. Only fill accumulator with dry nitrogen.
CAUTION
Never fill an accumulator with air. When air is
compressed, water vapor condenses and can cause
corrosion. This corrosion may damage seals and ruin
the accumulator.
MU1971
2
3