FTTH project OSP notes: Duct Integrity Testing (DIT)

“All team members MUST wear eye protection during DIT testing as small particles can be blown out of ducts through the holes in the DIT catcher.” keyword: Outside plant (OSP)

Duct Integrity Testing (DIT) for fiber cables

  If you have no ideas about what is this fiber cables DIT (Duct Intergrity Testing), please check bottom’s project video for reference. After backfilling ducts shall be tested for fiber cable’s integrity. Four types of tests are conducted:

  1. Air Tightness Test
  2. Foam Sponge Test
  3. Mandrill Test
  4. Pressure Test
Which test are they doing?

Which test are they doing?

First, Air Test

  • Fit a DIT catcher on the far side and equip personnel with two-way radios.
  • Allow the air to flow through duct for at least one minute, to remove all loose particles and/or moisture.
  • Now proceed with the sponge test.
    outside work: Duct Integrity Test

    outside work: Duct Integrity Test

Second, Foam Sponge Test – cleaning the duct:

  • A sponge is typically 100mm in length and 2 x the duct ID.
  • Wet the sponge slightly with blowing lubricant.
  • Place the tight-fitting foam sponge inside the microduct.
  • At a pressure of 10bars, blow the sponge through the microduct.
  • If excess water or dirt exits the microduct, repeat the process.
  • Have a DIT catcher in place at the far end to catch the sponge when it emerges.
    Duct Integrity Test DIT

    Duct Integrity Test DIT

Third, Mandrill Test – check for bends, kinks or blockages:

  • The sponge test MUST precede this test – a mandrill can damage a dirty duct.
  • Use a 40mm long mandrill made from Nylon or Teflon.
  • The OD must be no more than 85% of the microduct ID
  • At the receiving end, a DIT catcher must be used.
  • Note that a flying shuttle can cause injury and/or damage!
  • Always inspect the condition of the emerged mandrill, visible grooves is an indication of duct indents.
    FTTH Project OSP

    FTTH Project OSP

Last, Pressure Test – check for coupler leaks or microduct punctures:

  • Fit a high-pressure end-cap to the duct under test on the far-side.
  • Gradually build the pressure up to 10 bars.
  • Test all coupling used for this test for leaks, using soap, water and a sponge.
  • Connect the air feed and leave this open until the pressure in duct stabilizes at 10 bars.
  • Close the air valve on the test assembly and monitor the pressure gauge for 5min.
  • Losing 1 bar in 5min is acceptable – any leak greater than that, must be found and fixed.

  If the duct fails DIT tests, consult with the relevant authority on whether to use an alternative duct or to repair of the designated duct.

What is DIT (Duct Integrity Testing)?

Read more FTTH Outside plant (OSP) installation details!

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