◼ Note that with a low-pressure range piezometer (less than 350 kPa), it is
recommended that vibrating wire readings be taken with a VW2106 Readout
Unit while the filter housing is being pushed slowly into place, to ensure that
the sensor does not over-range due to this operation.
• The vibrating wire piezometer should be stored in the bucket of water until ready
to install downhole to maintain the filter saturation prior to installation.
• During the installation, the vibrating wire piezometers should be handled as
gently as possible to keep the water in the filter sinter and the bottom chamber
until submerging in the borehole.
CAUTION: VIBRATING WIRE PIEZOMETERS CANNOT BE ALLOWED TO FREEZE WHEN
FULLY SATURATED, OTHERWISE DAMAGE WILL OCCUR TO THE TRANSDUCER
DIAPHRAGM, WHICH WILL INVALIDATE THE TRANSDUCER FUNCTION AND
CALIBRATION.
The O-ring providing the friction fit may become worn and the filter housing may
become loose if the vibrating wire piezometer must undergo multiple removals and
reinstallations of the filter housing. Replace the O-ring immediately if the filter
housing is loose.
Coarser screen housings are available for use on vibrating wire piezometers if salts
or other precipitates are clogging the stainless sinter filter. Screens are less likely to
become clogged by precipitates and other debris found in some water sources.
Note that salts and other dissolved solids can be deposited within a stainless
sintered filter if the filter is allowed to dry out completely. Thoroughly rinse out the
filter with clean distilled water prior to drying to prevent filter clogging.
5.3 HIGH AIR ENTRY CERAMIC FILTERS
The ceramic filter on high air entry piezometers is also removable for de-airing.
Because of the high air entry characteristics of the filter, proper de-airing is
particularly important for this type of filter assembly in order to ensure that accurate
readings can be taken. High air entry filters are available with different air entry
values, which will require different procedures. It is therefore very important to know
which type of high air entry filter is installed.
5.3.1 One Bar High Air Entry Filters
1 Remove the filter housing from the piezometer body by carefully twisting and
pulling on the filter housing assembly. Remove the filter housing slowly to avoid
causing a vacuum pressure on the piezometer diaphragm.
2 Boil the filter assembly in de-aired water for 30 minutes to force all air out of the
filter and to saturate the filter material. Place the filter into de-aired water when
boiling is completed.
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