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3. SATURATING FILTER TIPS
Warning! Do not allow the piezometer to freeze once the filter stone has been saturated!
See Section 4.9 for information about protecting the piezometer from freezing.
Most filter tips can be removed for saturation and then reassembled. To maintain saturation, the
unit should be kept underwater until installation. If the piezometer is used in a standpipe where it
will be raised and lowered frequently, the filter housing may loosen over time, and a permanent
filter assembly may be required. The removable filter may be fixed permanently by prick
punching the piezometer tube approximately 1/16" to 1/8" behind the filter assembly joint.
Salts in the water can be deposited into the filter stone causing it to become clogged if it is
allowed to dry out completely. Filter stones may be replaced with screens for standpipe
installations. Screens available from Geokon are less likely than standard filters to collect salt
and become clogged.
3.1 Saturating Low Air Entry (Standard) Filters
For accurate results, total saturation of the filter is necessary. As the piezometer is lowered into
the water, water is forced into the filter, compressing the air in the space between the filter stone
and the pressure sensitive diaphragm. After a period of time, this air will dissolve into the water,
filling the filter and the space above it entirely with water.
To speed up the saturation process, remove the filter from the piezometer by carefully twisting
and pulling on the filter housing assembly (or unscrewing the point of the piezometer for model
3400DP). Hold the piezometer with the filter facing up and fill the space above the diaphragm
with water. Slowly replace the filter housing, allowing the water to squeeze through the filter
stone as it is installed. For piezometers with a range of less than 10 psi, take readings with a
readout box while reinstalling the filter housing to ensure the piezometer is not overranged.
3.2 Saturating High Air Entry Ceramic Filters
Because of the high air entry characteristics of the ceramic filter, de-airing is particularly
important. Different air entry values require different saturation procedures.
3.2.1 One Bar Filters
1) Remove the filter from the piezometer by carefully twisting and pulling on the filter
housing assembly.
2) Boil the filter assembly in de-aired water.
3) Reassemble the piezometer under the surface of a container of de-aired water. Use a
readout box while installing the filter to monitor the diaphragm pressure. If the
piezometer begins to overrange, allow the pressure to dissipate before pushing further.
4) Be sure that no air is trapped in the transducer cavity.
3
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