62
Magtrol WB/PB Dynamometers
Chapter 3 – Cooling
°dH
= German hardness degree
= 10 mg CaO/liter
°THfr = French hardness degree
= 10 mg CaCO
3
/liter
°eH
= English hardness degree
= 1 grain CaCO
3
/gallon
°THus = American hardness degree
= 1 mg CaCO
3
/liter (ppm)
1 °dH = 1.79 °THfr = 1.25 °eH = 17.9 °THus
C
aution
:
n
ever
use
demineralized
water
for
the
Cooling
of
dynamometers
as
this
water
is
aggressive
and
leads
to
Corrosion
due
to
a
high
Content
of
free
Carbon
dioxide
.
3.4.3
F
iltering
In order to avoid clogging of the cooling system due to sand, mud, rust or other substances, the
installation of a filter at the water inlet is recommended.
Solid substances conveyed by the cooling water should not exceed 250 microns. As a rule, the filter
should remove approximately 98% of the substances above 250 microns of diameter.
3.4.4
c
ontrolling
the
W
Ater
F
loW
r
Ate
An excessive deposit of minerals may be avoided by limiting consumption to the absolute minimum
necessary for the dynamometer braking power dissipation. This may be performed by installing a
thermostatic valve on the water outlet and by adjusting it just below the cutoff temperature of the
dynamometer safety thermostat (approximate setting ~50 °C or 120 °F). This valve must constantly
guaranty a flow rate in order to get enough water flowing to the dynamometer safety thermostat.
3.4.5
W
Ater
i
nhiBitorS
In order to prevent scale from forming in closed-circuit cooling circuit systems, it is sometimes
necessary to use water inhibitors which must be effective against rust, corrosion and mineral deposits.
The use of strong alkaline substances or certain acids may be risky and dangerous during
manipulations. These substances can attack the different metals of the dynamometer, and may even
be toxic to the operator.
•
Chromates:
should not be used as they cannot avoid mineral deposits and do not protect
aluminum. Furthermore, they are acid-based, dangerous and toxic.
•
Borates:
should not be used as they cannot prevent deposits from forming.
•
Phosphates:
should not be used as they will cause algae growth.
•
Chlorides
,
nitrates
and
sulfates:
should not be used as they will cause corrosion.
If the available water proves to be of questionable quality, the user should contact the local authorities
to be informed about an adequate form of water treatment. Special attention should be paid to water
found in industrial areas where contained polluting substances may represent a source of potential
dangers for the dynamometer cooling system. Furthermore, water inhibitors improperly used can
have a negative impact on the environment.