26
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November - December 2015
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www.machinerylubrication.com
What do you normally cover in
your plant's safety meetings?
Personal protective equipment,
chain guards, safety harnesses and lock-
out-tagout procedures are common topics.
When was the last time hydraulic accumu-
lators were discussed? If your plant is like
most, the answer is never. Why? In most
plants, maintenance, production and
safety managers are not aware of the
dangers. Nevertheless, accumulators can
present a safety hazard if the potential risks
are not understood.
Accumulator Function and
Pre-Charging
An accumulator is a storage device in a
hydraulic circuit. It is the hydraulic equivalent
of a capacitor in an electrical circuit. The two
most common kinds of accumulators are the
bladder and piston types. The bladder (Figure
1) is nothing more than a rubber balloon that
separates the hydraulic oil from the dry
nitrogen. Dry nitrogen is used to fill the inside
of the bladder to a pre-charge level. The
nitrogen pre-charge is usually half to two-thirds
the maximum pressure in the system.
When the pump is turned on, the
nitrogen is compressed to the maximum
pressure in the system. The setting on the
pump compensator spring will determine
the maximum pressure when a pres-
sure-compensating pump is used. The
relief-valve setting controls the pressure in a
fixed-displacement pump circuit.
In Figure 2, the bladder accumulator has
been pressurized to 2,000 pounds per
square inch (psi).
The piston in a piston-type accumulator
(Figure 3) separates the nitrogen from the
hydraulic oil. When oil is ported into the
By Al Smile y, GPm HydrAulic conSultinG
HYDRAULICS
Dangers of
Hydraulic
The Safety
Accumulators
1000
PSI
PSI PSI
0
2000
A
B
2000
PSI
Figure 1. Bladder accumulator Figure 2. Bladder accumulator
pressurized to 2,000 psi
Figure 3. Piston-type
accumulator
