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Silt Density Index Test
Instructions
Equipment
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Silt Density Index Test Assembly (AMI DIRECT SDI - Model No. SDI-2000)
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Filter Holder
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Pressure Gauge
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Pressure Regular
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Ball Valve
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Graduated Cylinder
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Thermometer
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Tubing
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Filter Tweezers
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Stop watch or other means of timing (not included)
Procedure
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Unbolt the filter holder, wet it, and place a 0.45 micron
filter on the back-up plate using the dull tweezers.
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Place the "O"-ring properly and then replace the top half of
the filter holder and bolt loosely.
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Connect apparatus to the feedwater line (minimum 30 PSIG) in a
vertical, downflow position and open the needle valve a crack.
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Loosen two adjacent filter-holder bolts, tilt the apparatus
and bleed out all trapped air, then retighten bolts and adjust the pressure to
30 PSI while starting the stopwatch.
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Immediately run the flow into the graduated cylinder and
measure the time required to collect 500 ml, maintaining a pressure of 30 PSIG
during the run. Mark the time (t1)
and keep the watch running.
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Repeat the previous step immediately after 5, 10, and/or 15
minutes of total elapsed time. Mark the collection times (t5,
t10,
tF).
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Close the sample valve and disconnect the apparatus after the
15 minute reading. Remove the disk and place it in a plastic bag for later
examination.
Calculation
Calculate the ratios R = t1/t5
, t1/t10
and/or t1/tF.
Estimate % P30
at the selected time(s) from the following equation:
% P30
= [1-R] × 100.
Estimate the Silt Density Index, SDI, from the following equation:
SDI = % P30
÷ Elapsed Time (minutes)
The 15-minute index will generally be the lowest of the three, and
should be used for filter sizing purposes.
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