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Direct SDI - Silt Density Index Test Kit
Silt Density Index Test Assembly

Completely assembled in a portable, compact case, ready for on-site testing. Includes ASTM instructions for measuring silt density index. Minimum of 30 PSI water pressure required. Optional Pump Assembly Kit available for pressures below 30 PSI.

Model Number:  SDI-2000

Assembled with:

  • Filter Holder
  • Pressure Gauge
  • Pressure Regulator
  • Ball Valve
  • Graduated Cylinder
  • Thermometer
  • Tubing
  • Filter Tweezers


Click Here to Purchase our SDI Kit Online

Also Available:

  • Manual SDI Kit with Milipore brand filter holder - Model No. SDI-2000-MIL


  • Pump Assembly Kit for testing with less than 30 psi. Assembled with Booster Pump, Power Supply, and Pressure Regulator. This is available in three voltages:
    • SDI-PU: 115-120VAC, 60Hz
    • SDI-PE: 230VAC, 50Hz
    • SDI-PJ: 100VAC, 50-60Hz

 (Filters not included - see below)

Spare Parts for Silt Density Index Kits

AMI Model No.
Filters for SDI Testing 0.45 Micron, 47 mm, package of 100
Filter Holder for SDI Kit



What is SDI?

Suspended solids and colloidal materials in feed water are one of the biggest problems in reverse osmosis systems.

Although most systems have some pretreatment, including 5-micron prefilters, these fine particles are responsible for the fouling of reverse osmosis membranes.

In order to have some measure of the degree of this fouling problem, a concept called Silt Density Index is used. Here a 0.45 micron filter is exposed to the feed water under pressure and filtration rates are calculated.

An SDI of less than 5 is considered acceptable for the reverse osmosis systems. This means that at values of SDI of less than 5, the membranes should foul at a very low rate. Even though the concept works most of the time, there are exceptions when a lower SDI (less than 3) is desirable due to the nature of the suspended solids in that feed water.

To perform the test, a new filter is placed in the filter housing, and the operator times and records how long it takes for the water flow to fill a pre-set volume in a graduated cylinder.  The water is then allowed to run through the filter for a predetermined amount of time, and then the amount of time it takes to fill the same volume is recorded again.  This indicates amount of 'clogging' that has occurred during the elapsed time, and the SDI of the water can be calculated from these figures.   Click here for the detailed test procedure.

Silt Density Index Test


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