Application and calculation method of SDI detection in purified water equipment

1. Install SDI tester on the test position of RO system of purified water equipment. If the test point is after preprocessing the system, the RO system should run normally when testing the SDI value, otherwise the final test result will be invalid.

2. At the beginning, 0.45 μ microporous filter membrane cannot be placed in SDI tester.

3. After the tester is connected, open the valve on the tester and let the tested water flow directly through the tester for several minutes.

4. Close the valve, put a 0.45 μ white microporous filter membrane (bright side up) on the membrane box support plate of the tester with special tweezers, press the "0" ring and the upper cover of the membrane box lightly, and screw on the plastic screw, but not too tight.

5. Open a part of the valve. When the water flows through the tester, slowly loosen one or two plastic screws to let the water diffuse out of the tester to eject the air in the tester.

6. Make sure there is no air in the tester, and tighten the plastic screw slightly. Fully open the valve, adjust the pressure of the pressure reducing valve to 0.2MPa (207kpa), keep the pressure and close the valve. The pressure must remain constant throughout the test.

7. Collect water samples in a suitable container. As long as the same capacity is used for each test, the size of capacity is not important. The capacity can be between 100 and 500 ml. Different containers are available: measuring cylinder, large cup, coffee cup, Coca Cola bottle, etc. It is generally considered to collect 500ml water sample.

8. Fully open the valve, use the stopwatch to measure the time required to collect 500 ml of water sample, and record it as t (1) = uuu second. After collection, keep the valve open to let water flow out.

9. After 5 minutes, use a stopwatch to measure the time needed to collect another 500ml water sample and record it as t (5) = A S. after 10 and 15 minutes, do the same test and record it as t (10) and t (15), respectively. After the test, the SDI value can be calculated. Some water sample data sampling may be required to continue to t (20), t (30) or even t (60), of course, this kind of water sample is very few.

10. Measure the water temperature. The water temperature must be consistent throughout the test.

11. SDI value is calculated by the following formula:

SDI = 100p30 / TT = 100 (1-t1 / T2) / TT

P30 - plugging index under 207kpa water inlet pressure;

The total test time (score) of TT is usually T15, when P30 is less than 75%, otherwise test T10 or T5, so that P30 is less than 75%.

T1 - time required to collect 500ml water sample at the beginning (seconds);

T2 ---- time (s) required to collect 500ml water sample after T1 (usually T15, i.e. 15 minutes).