5.3 - Repair
46
SBT-2400 Service Instructions
M2041/5en
©BTG 2006
5.3.5
Measuring Module O-Ring Seal Replacement
NOTE!
Replacing this O-ring seal is complicated, because it have impact on the
transmitters calibration. This should be done by BTG qualified personnel.
The O-ring seal in the measuring module is used to prevent fibers and other
impurities penetrating and blocking the spindle movement. Note that fluid is al-
lowed enter the cavity behind the O-ring, but not any further. This does not af-
fect the transmitter performance.
The standard O-ring seal is made of a fluorine-type rubber material developed
for the pulp and paper industry and have an extremely high resistance to all
chemicals.
As an option the O-ring seal is available in EPDM quality. EPDM is recom-
mended in applications where the pH level is high (more than 12), for example
unwashed sulfate pulp, or hydro peroxide (H
2
O
2
) bleach plant applications
with high pH.
The O-ring seal is a low cost spare part and it is easy to replace. It should be
replaced as a preventive action when aggressive chemicals are present and
also when very reliable measurements are required.
The O-ring seal is replaced when:
•
The transmitter is gradually drifting and has lost sensitivity.
The rubber in the O-ring seal has been chemically attacked and lost its
original properties.
Verify that correct quality is used.
NOTE!
Drift can occur for numerous reasons; change of fiber type, freeness level,
temperature, flow velocity, or other process related parameters.
