ABB KM26 Operating Instruction page 11

KM26 | M AG N ET I C LE V EL G AUG E | O I/KM 2 6 -EN RE V I
. . . 3 Mounting
Floats
The float is a strong capsule that is engineered for the
temperature and pressure conditions of an application and
designed to be precisely buoyant in a liquid or liquids
(interface). The float follows the surface of the process fluid
or liquid-liquid interface as the level in the chamber
fluctuates. The float interacts magnetically with a visual
indicator mounted on the outside of the chamber to reveal
the liquid level inside. Communicating the fluid level
information using the float's magnetic field isolates the level
indicator from the process allowing for longer lasting, error-
free operation of the KM26 MLG.
The float (figure 11) is a key component of the KM26 MLG and
is engineered to match the medium in respect of density,
pressure resistance and material durability. Every float is
precisely engineered to customer application, ensuring
optimal accuracy and performance. Precisely spaced magnets
create a 360° magnetic field coverage, safeguarding level
transmitter and gauge performance, even the most
challenging applications. Several materials of construction
available including titanium, Monel®, Hastelloy® C, stainless
steel, and plastics. Tefzel®, Halar®, TEFLON® S protective
coatings are also available. The float is equipped with a ring
system of permanent magnets for transmission of liquid level
to the indicator. The indicator is linked magnetically to the
magnet system in the float. During installation, it may be
necessary to remove the float from the chamber. For proper
operation, the float must be reinstalled using the proper
orientation. Floats may be marked with 'top for SPM' or floats
may be marked with an arrow indicating the proper
orientation.
KM26S float is shipped inside the chamber unless specified
for separate shipment. Most floats are labeled to indicate the
top of the float, the specific gravity of the fluid and the serial
number of the chamber for which they are designed. If the
float is coated, labeling is not performed and the float should
stay with the chamber. The top of the float can be found by
locating the magnet placement and direction with respect to
the indicator in the scale. The indicator should be attracted to
the float, not repelled, when inserted correctly.
The KM26T float is wrapped separately in bubble wrap. The
magnet assembly at the end of the float rod is inserted into
the top of the guide chamber unless the float rod is too long,
in which case it will be shipped outside of the guide chamber.
The stop tube and disk are installed over the rod end and into
the chamber. Then, the snap ring is inserted into the internal
groove to hold the assembly in place. Finally, the float is
threaded onto the rod and locked in place with the nut
provided.
Float Stop Springs
Springs are often included in the top and bottom of a the
MLG chamber. The primary purpose is to provide protection
for the float during operation and shipping/handling. If
pressure rapidly enters the chamber (possibly due to a quickly
opened valve), the float could be propelled toward the top of
the chamber at a high rate of speed. The spring will dampen
the impact and assist in protecting the float from damage.
Figure 11 - KM26 MLG floats
If specific gravity decreases, the float will have more of its
length below the fluid level and give a visual indication that is
lower than actually exists. If the fluid specific gravity has
significantly changed after the unit has been placed in
service, it may be necessary to replace the float in order to
allow for accurate level indication. This can change the length
and magnet position of the float. The stop springs must be
adjusted accordingly. On the KM26S this is accomplished by
either stretching or compressing (or cutting) the bottom and
top springs. The scale may also have to be adjusted to
coincide with the floats' new zero position. To adjust the zero
for the KM26T, the float stop tube can be elongated or
reduced.
CAUTION
Do not weld on MLG or on the vessel with indicator and
float installed, this will damage the magnetic circuit.
The chamber must be vertically level (plumb) to insure proper
operation of the float and its follower. A unit that is not
leveled properly may decouple unexpectedly due to friction
with the sides or because the float travels too far away from
the indicator.
NOTICE
The end user must provide adequate structural support
for the chamber in the field. It is recommended that, for
longer chambers (and especially for non-metallic
constructions), support brackets attached to the side of
the level gauge are placed at minimum intervals of 6 feet.
11