Alfa Laval LeviMag, Instruction Manual, Page: 37 / 68

7 ATEX specific conditions for safe use
7.1 Recommendation
Alfa Laval recommend while operating with ATEX to use an inert gas in the vapor space in the tank to eliminate all possible
ignition hazards. The installation must be according to the requirements for safety use of an inert gas.
7.2 Requirements
If is not possible to use an inert gas as recommended - the following requirements must be met before using the mixer in an
ATEX classified zone:
A. The impeller must always be submerged during operation since dry running will result in a temperature increase in the
bearing surfaces and potential ignition source can become effective. With the impeller submerged, the mixer is not
subjected to any gas inside the tank and is therefore outside any classification zone – even though the inside of the tank
can be ATEX classified to a zone.
To prevent dry running, a level switch must be installed to shut down the mixer.
Follow section 7.5 Positioning of level switch to install the equipment.
Ensure the liquid level during operation is always above the impeller to prevent dry running.
B. The properties of the fluid and the speed of the mixer are limited to prevent the mixer from losing the magnetic coupling – if
the limitations are not followed a potential ignition source can become effective.
The properties of the liquid are limited by the following:
-
fluid must be Newtonian
- maximum density: 1.1 g/cm
3
- maximum viscosity: 50 cP
Ensure that there is enough conductivity in the liquid to avoid the risk of electrostatic charging and an ignition hazard.
With the above fluid restrictions, the following maximum speed limits must be respected and must not be exceeded in relation
to the selected impeller diameter:
Weld plate Impeller Maximum speed
50 100 800 RPM (80,8 Hz)
50 150 436 RPM (44,1 Hz)
81 200 446 RPM (76,9 Hz)
81 250 230 RPM (39,6 Hz)
81 300 182 RPM (31,3 Hz)
Ensure the mixer cannot generate mechanical sparks in an ATEX classified zone by hitting the tank wall or other equipment in
the tank.
C. To prevent developing a vortex which reaches the impeller when there is an ATEX zone above the media level, the maximum
speed must be evaluated depending on the specific tank dimension.
To prevent the mixer operating with a higher speed than specified according to section 7.5 Positioning of level switch make
sure to follow section 7.4 Monitoring the frequency converter .
NOTE
If the operating limits are to be exceeded it can lead to an ignition source coming affective, either by the mixer loses the magnetic
coupling, resulting in mechanical contact to the wall, otherwise through a vortex or dry-running heat can buildup in the bearing
surfaces, resulting in exceeding the assigned temperature class of the product.
37