The choice of the elastomer used for the bladder depends on the liquid to be used and on the operating temperatures
(and at times, storage). In the chart below, each polymer has a designated letter to be used in the ordering code.
Code
letter
E
Polymer
ISO
EPDM
Temperature
range (°C)
-20 +90
to
Some of the liquids compatible with the polymer
N
CR
-20 +85
to
V
FKM
-20 +121
to
Break fluids, hot water, leaching fluids, detergents, water-glycol
(HFC), many acids and bases, saline solutions, skydrol 500, etc.
Freon (12-21-22-113-114-115), water and aqueous solutions,
ammonia, carbon dioxide, mineral, paraffin and silicon oils.
The same as with standard nitrile but with excellent performance at
both high and low temperatures.
P
NBR
-20 +85
to
F
NBR
-40 +70
to
H
NBR
-10 +90
to
Mineral, vegetable, silicon and lubricating oils, industrial water,
glycols,
non-flammable
liquids
(HFA-HFB-HFC),
aliphatic
hydrocarbons, butane, diesel oil, kerosene, fuel oils etc.
The same as with standard n a number of different types
of Freon. (This contains less acrylonitrile than the standard and is
therefore more suitable for low temperatures, but is chemical
resistance is slightly lower.
The same as with standard nitrile + regular and premium grade
slightly aromatic gasoline.
K
HNBR
-50 +130
to
A
NBR
-20 +85
to
B
IIR
-20 +90
to
The same as with standard nitrile but with excellent performance
at both high and low temperatures.
Foods (specify which type when ordering).
Phosphoric esters (HFD-R), phosphate esters, fyrquel, hot water,
ammonia, caustic soda, some kinds of Freon (22-31-502), glycol-
based brake fluids, some acids, alcohols, ketones, esters, skydrol
7000, etc.
Y
ECO
-30 +1 0
to
0
Lead-free gasoline, mineral oils.
Nitrile (Buna-N
/ Perbunan)
Ethylene-
Propylene
Low Temperature
Nitrile
For food-stuffs
Butyl
Nittrile for
Hydrocarbons
Chloroprene
(Neoprene)
Epichloridrin
Viton
(Flouroelastomer)
Hydrogenated
Nitrile
The precharge pressure P
- In most cases the values
0
recomended in Gas Precharge Pressure - page-3 are valid
although, as the pressure and, above all, the velocity of the
yield required increase, there is the danger that in each
cycle the bladder will knock against the poppet valve. In
these cases it is possible to use P = 0.8 to 0.7 P .
0
1
The P /P ratio
- Any increase in this, will increase the
2
0
stress the bladder is subjected to in each cycle.
The maximum operating pressure P
- Any increase in
2
this will subject the bladder to greater stress.
Flow rate -
Flow rate does not affect bladder working life if
values given in Table.2 are not exceeded. When
approaching the maximum values, make sure there
remains a residual volume of liquid > 10% of the volume V
0
in the accumulator, in both loading & unloading conditions.
The frequency
or number of cycles per day.
Installation
- The vertical position with gas valve on top is
the recommended arrangement. When the position is
horizontal the bladder tends to rest and rub against the
accumulator body. This could result in quicker wear.
The operating temperature
- This is one of the factors
which most affects the life of the bladder: at very low
temperatures the bladder tends to become brittle; as the
temperature rises, reaching, or going beyond the limits for
the elastomer, the stress the bladder is subjected to
increases exponentially, which can lead to fracturing within
a short time.
It should be remembered that the temperature in the
accumulator is in many cases higher than the one of the
system, and that it rises with each increase of P , of P /P ,
2
2
1
and with the volume of the accumulator (in other words,
larger the accumulator, lesser is the capacity to dissipate
heat).
Durability of the Bladders
It is essential, in order to make the correct choice, to take into consideration the working conditions that the bladder will be
operating in, because these can considerably affect the durability of the bladder. Assuming that the liquid used is
clean
and compatible with the bladder material, there are a number of factors which can affect the life of the bladder:
Material
Bladder - Material | Durability
* Check availability before ordering.
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