Accumulators; General Information - JLG sky trak mmv Service Manual

Hydraulic System
9.13

ACCUMULATORS

This section covers the testing and charging of the accu-
mulator system.
The accumulators (1) are located under the engine cover
and are mounted to the top of the hydraulic oil reservoir
(2). The internal parts of these accumulators are not ser-
viceable. If the internal seals on the "free floating" piston
are leaking or the seals on the top or bottom cap are leak-
ing the accumulator requires replacement.
1
2
9.136
9.13.1

General Information

Each accumulator is a 4000 psi (276 bar) piston type ac-
cumulator. Each accumulator has an oil volume of 53 cu-
bic inches and a gas volume of 58 cubic inches, with a
bore size of three inches.
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 "free floating" pis-
ton. This piston prevents the mixing of gas and oil and
keeps the gas out of the hydraulic system. The piston fits
into a smooth bore and uses seals to separate the gas
from the oil. O-rings on both end caps prevent leakage of
the gas or oil.
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 700 +50/-
0 psi (4826 +345/-0 kPa). The gas valve (3) located under
the protective cap (4) at the top of the accumulator. The
gas valve is used for pre-charging and testing the accu-
mulator.
MM4450
4
Model MMV Rev. 12/04
3
MM4500