Why does it matter which side of the membrane is used as the feed side? The update addresses a deficiency and in our opinion corrects an error that has existed since the standard was first released in Perhaps the most critical component of the SDI test is the membrane filter used in the test. Previous versions of the standard had defined the membrane as follows: 6.
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A number in parentheses indicates the year of last reapproval. Some filter holders include a foam support pad,which should be used. Place the filter grid side up. Handle themembrane filter only with dull tweezers to avoid puncturing. Avoid touching the membrane filter with the fingers.
NOTE 1—Other membrane filter sizes, that is, 25 mm or 90 mmdiameter, can be used. Replace the top half of the filter holder and closeloosely. Closethe valve and tighten the filter holder.
Simultaneously, using a stopwatch,begin measuring the time required for the flow of mL. Record the time ti. Leave the valve open for continued flow. The nonplugging reference water can be obtained byfiltering distilled water through a 0. If a different filter size is used, adjust the sample size in direct proportionto the filter area. Measure the watertemperature and check the pressure as each sample is collected Note 7 and Note 8. Precision and Bias The pooled single operator precision is 0.
The test method is very sensitive to bothquantity and size of suspended particles, which contribute tothe plugging of the membrane filter. Maintenance of theintegrity of the samples cannot be guaranteed through prepa-ration of the bulk mix, subsampling for testing, shipping, andholding.
Moreover, approximately 5 gal of sample are requiredfor each SDI test run. Thus, if large stock solutions exhibitingdifferent SDI values could be prepared and if representative 30to gal subsamples could be drawn, shipping two or three ofthese samples to each of six or more laboratories for full-scaletesting was not considered to be practical.
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