and the system pressure can be maintained within
an acceptable range for long periods of time.
Accumulators also compensate for thermal
expansion and contraction of the liquid due to
variations in temperature.
A liquid, flowing at a high velocity in a pipe
will create a backward surge when stopped
suddenly by the closing of a valve. This sudden
stoppage causes instantaneous pressures two to
three times the operating pressure of the system.
These pressures, or shocks, produce objectional
noise and vibrations which can cause considerable
damage to piping, fittings, and components. The
incorporation of an accumulator enables such
shocks and surges to be absorbed or cushioned
by the entrapped gas, thereby reducing their
effects. The accumulator also dampens pressure
surges caused by pulsating delivery from the
There are times when hydraulic systems
require large volumes of liquid for short periods
of time. This is due to either the operation of large
cylinders or the necessity of operating two or more
circuits simultaneously. It is not economical to
install a pump of such large capacity in the system
for only intermittent usage, particularly if there
is sufficient time during the working cycle for an
accumulator to store up enough liquid to aid the
pump during these peak demands.
The energy stored in accumulators maybe also
used to actuate hydraulically operated units if
normal hydraulic system failure occurs.
Four types of accumulators used in Navy
hydraulic systems are as follows:
1. Piston type
2. Bag or bladder type
3. Direct-contact gas-to-fluid type
4. Diaphragm type
Piston-type accumulators consist of a
cylindrical body called a barrel, closures on each
end called heads, and an internal piston. The
piston may be fitted with a tailrod, which extends
through one end of the cylinder (fig. 9-5), or it
may not have a tailrod at all (fig. 9-6). In the latter
case, it is referred to as a floating piston.
Hydraulic fluid is pumped into one end of the
cylinder and the piston is forced toward the
opposite end of the cylinder against a captive
Figure 9-6.Floating piston-type accumulator.