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PRODUCT INFORMATION

Silt Density Index (SDI) Testing Technique

Product Information

Silt Density Index (SDI) Testing Technique

Technical explanation

Test Method for Determining the SDI Sedimentation Index

Equipment preparation:
• 0.45 micron filter disc and filter holder.
• 500ml graded cylindrical container
• Stopwatch
• Passivated forceps

testing method:
• Unwrap the filter disc holder, wet it, and place a 0.45 micron filter disc on the backup plate using passivated forceps.
• Position the "O" ring correctly, then replace the top half of the filter pan holder and loosen the bolts.
• Connect the unit to the water inlet pipe (30 PSIG minimum) in a vertical position and slightly open the needle valve.
• Loosen the two adjacent filter valve bolts, tilt the unit and expel all trapped air, then retighten the bolts and adjust the pressure to 30 PSI while starting the stopwatch.
• Immediately run the flow into a graded cylindrical vessel 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.
• Repeat the previous step immediately after 5, 10 and/or 15 minutes of total use. Mark the collection time (t5, t10, tF)).
• After 15 minutes, close the sample valve and disconnect its device. Remove the filter disc and place it in a plastic bag for later inspection.

Calculation method:
• Calculate the ratios R = t1/t5 , t1/t10 and/or t1/tF.
• Use this equation to estimate the percentage of P30 for the selected time: % P30 = [1-R] x 100.
• Use this equation to estimate the sedimentation index SDI: SDI = % P30 = elapsed time (minutes)

Note: The 15-minute index is usually the lowest of the three and should be used for filter sizing purposes.

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