Fire-Resistant Hydraulic Fluids - Parker O-Ring Handbuch

7. Applications
Medium Old abbr.
Vegetable oil HTG
(triglycerides)
non-water-
soluble
Polyalkylene HPG
glycol
water-soluble
Synthetic ester HE
Polyalphaole- --
fines
(synth. hydro-
carbons,
non-water-
soluble)
For operating temperature limits please refer to manufacturers' instructions.
*
Table 7.7 Environmentally harmless pressure fluids
% was noted in particular. This may lead to considerable func-
tional performance problems and, perhaps, all the way to seal
failure. The potential effects on the performance of seals must be
shown by future field experience.
Table 7.8 lists the compounds that can be recommended for the
aforementioned fluids based on currently available knowledge.
In the category of polyalkylene glycols (HEPG) a large number of
fluids based on polyethylene oxide and polypropylene oxide as
well as mixtures of these two are available.
Generally, for systems using HEPG fluids the use of polyurethane
seals is not recommended. On the whole, the possibility of water
entering the hydraulic circuits of mobile machinery and equip-
ment cannot be excluded. In a lab test of NBR and HNBR com-
pounds at 100°C and 168h resp. 1000h the effects of a 1 % water
content in a vegetable oil (HETG) and a synthetic ester (HEES)
on the sealing compounds have been determined. With both
compounds an exceptionally high volumetric swelling of app. 20
< 80°C
HETG AU , NBR, HNBR,FKM
1
HEPG NBR , HNBR ,FKM
1 2
HEES AU , NBR ,HNBR
1 1
HEPR NBR ,HNBR , FKM
1 1
to be tested for the particular application
1
only if medium has no ester admixture
2
Table 7.8 Recommended elastomers for industrial uses, test period 168 + 1000h
(ISO 6072) , environmentally harmless pressure fluids
Abbr. acc. to the 7th
Luxemburg Report,
DIN 51502 and ISO
6743/4
HETG
HEPG
HEES
HEPR
< 100°C
N/A
HNBR ,FKM
2 1
,FKM HNBR ,FKM, AU
1 1 1
, AU HNBR , FKM , AU
1 1 1
Application
Operating tempera-
tures*
Hydrostatic drives, mobile
hydraulics
-20°C to +70°C
Hydrostatic drives, hy-
draulic systems for locks
-30°C to +90°C
Hydrostatic drives, mobile
and industrial hydraulics
-35°C to +90°C
Hydrostatic drives, mobile
and industrial hydraulics
-35°C to +80°C

7.13 Fire-resistant hydraulic fluids

When mineral oils represent a high fire risk, fire-resistant hydrau-
lic fluids are used. Three groups of such fluids are described in
VDMA 24317 and 24320:
 water emulsions (HFA and HFB groups)
 water solutions (HFC)
 water-free synthetic fluids (HFD)
The types of fire-resitant hydraulic fluids are presented in table 7.9.
Fluids containing water rely on their water content to prevent
fire. To remain effective such fluids must be regularly checked
and their water concentration maintained. Working temperatures
are limited to between +50 °C and +65 °C because water eas-
ily evaporates at higher temperatures. All fluids containing wa-
ter have one common feature: they have a negative effect upon
bearings.
According to ISO 6071, groups HFA, HFB and HFC are differenti-
ated further by the suffix letters C, M, E and S:
 C indicates that no wear inhibitor is present
 M indicates that a wear inhibitor is present
 E indicates a mineral oil based HFA fluid
 S indicates a synthetic HFA fluid
Table 7.10 shows a comparison of the most important properties
of the four groups of non-flammable fluids together with the rec-
ommended type of elastomer.
145
Typical uses
Sanitary land fills/municipal
vehicles,
rail vehicles, farming and
forestry
Water protection zones, waste
water technology, tunnel/gallery
driving equipment, wet excava-
tors, offshore technology
Large-scale metal forming tech-
nology systems
Biodegradability is insufficient
O-Ring Handbook
Parker Hannifin GmbH
O-Ring Division Europe