1. Install the SDI tester in the test position of the RO system. If the test point is after the pre-processing system, then when testing the SDI value, the RO system should operate normally, otherwise the final test result will be invalid.
2. At the beginning, no 0.45μ microporous filter membrane can be placed in the SDI tester.
3. After the tester is connected, open the valve on the tester and allow the measured water to flow through the tester for a few minutes.
4. Close the valve and use a special tweezers to place a 0.45μ white microporous filter membrane (bright side up) on the tester's capsule support plate and gently press the “0†ring and capsule head. Screw on the plastic screw, but do not tighten it too much.
5. Open the valve and when the water flows through the tester, slowly loosen one or two plastic screws to allow the water to diffuse out of the tester and expel air from the tester.
6. Make sure there is no air in the tester, gently tighten the plastic screws. Open the valve completely and adjust the pressure of the regulator to 0.2MPa (207KPa). Hold the pressure and close the valve. The pressure must remain constant throughout the test.
7. Collect the water sample in a suitable container. As long as it is guaranteed to use the same capacity test each time, the size of the capacity is not important. The capacity can be between 100 and 500 ml. Different containers are available: eg measuring cylinders, beakers, coffee cups, Coca-Cola bottles, etc. Generally consider collecting 500 ml of water sample.
8. Fully open the valve and use a stopwatch to measure the time required to collect 500 ml of water and record it as T(1)=__ seconds. After the collection is completed, continue to keep the valve open and let the water continue to flow out.
9. After 5 minutes, use a stopwatch to measure the time required to collect another 500 ml of water sample and record it as T(5)=__ seconds. After 10 and 15 minutes, do the same test and record it as T. (10) and T (15). After the test is complete, the SDI value can be calculated. Some data sampling of water samples may be required to extend to T(20), T(30), or even T(60). Of course, such water samples are rare.
10. Determine the water temperature. Water temperature must be consistent throughout the test.
11. The SDI value is calculated from the following formula:
SDI=100P30/Tt=100(1-T1/T2)/ Tt
P30 - clogging index at inlet pressure of 207 kPa; Tt total test time (minutes) is usually T15,
At this point P30 <75%, otherwise test T10 or T5, so that P30 <75% at this time
T1 - time (in seconds) required to initially collect 500 ml of water sample;
T2 - The time (in seconds) required to collect 500 ml of water after T1 (usually T15, ie 15 minutes).
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