Service Manual 83
© 2018 Nortek AS
3.8.6 O-ring Care
Watertight sealing of the instrument housing is provided by double O-rings on the head and end cap
sub-assemblies. The outer O-ring forms the primary seal and the inner forms a secondary (or
backup) seal. If the integrity of the O-rings are degraded the instrument should not be re-deployed. In
this case, please contact us.
O-rings are the critical component that keeps water out of the housing and thus the instrument dry.
Make a routine of O-ring inspection, maintenance and replacement.
Check the O-rings and the O-ring grooves for grit, hair, lint, sand, or anything that could potentially
breach the O-ring seal.
After frequent deployments or if O-rings or groves appear dirty, remove O-rings and clean the
groves. To remove O-rings, use finger pressure or the rounded edge of a plastic card to lift the O-
ring out of the grove. Caution! Never use a metal object to remove an O-ring. It may cause damage
to the O-ring or the sealing surface.
To check O-rings for damage, place the O-ring between the middle and index finger and thumb.
Then pull the O-ring through your fingers, feeling for any debris or wear.
If O-rings are dirty, it is best to replace them. Washing dirty O-rings with soap and water is not
recommended. Soap breaks down the lubricants and will compromise the integrity of the seal.
Properly greased O-rings will help maintain sealing integrity and minimize O-ring degradation. Use
enough grease to lubricate the O-ring thoroughly, but not so much that it will attract additional
debris.
Clean the groove with a lint free swab or the folded edge of a paper towel.
3.8.7 Replace Desiccant Bag
Humid air can condense enough water do damage the electrical circuitry. At least once a year,
replace the desiccant located in the pressure case or the external battery canister. Refer to the
battery installation description for the procedure of opening the pressure case.
3.8.8 Biofouling
Marine growth, or fouling, on moorings should be considered when planning long-term mooring
systems. The thickness of growth depends on location (temperature, sunlight conditions, depth,
latitude, currents etc.). Fouling can be a problem already after 2 weeks in tropical areas or it can
take 6 months in cold areas. Sunlight is also an important factor - fouling is generally much less of a
problem below 100 m than it is at 5 m depth.
When calculating forces, the marine growth is accounted for by increasing the expected weight and
diameters of the mooring line and all instrumentation attached, in addition to increasing the drag.
Antifouling paints and other agents are often used to avoid transducers being covered with barnacles
or other evil crustaceans during long deployments. The important thing when it comes to antifouling
is that the paint is not too thick; otherwise, the signal strength may decrease. We tested the effect
on the profiling range of the 2 MHz Aquadopp and we could find no appreciable change when we
applied a thin (1 mm or so) layer on the transducers. You can probably use most anti-fouling paints
as long as it is not too (chemically) aggressive and contains no solids (metal flakes, etc.) that could
interfere with acoustic beams.
We realize barnacle has to be removed mechanically, but we strongly advice against using sharp
objects capable of harming the surface. We also recommend staying away from strong organic
solvents such as acetone.
A common, easy, and inexpensive way to keep the Delrin housing on the Vector clean is to wrap the
housing in either clear packaging tape and/or clear plastic wrap (such as the brand name "Seran
Wrap"). At the end of the deployment, simply unwrap the protective coating to find a clear
instrument. Tapes such as "Duct Tape" can leave a sticky residue that is very difficult to remove
(although it does not actually harm the Delrin housing).
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