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The Importance Of Duct Integrity Testing Prior To Fiber Cable Blowing And Everything You Need To Know

The Importance Of Duct Integrity Testing Prior To Fiber Cable Blowing And Everything You Need To Know


DIT, or Duct Integrity Test, is an extensive series of evaluation steps. It gets performed on the duct below the ground for putting or installing the optical fiber in the network. It is an integral and indispensable step that needs to be conducted between duct laying and pre-installation of cable jetting within the duct. The Duct Integrity Test apparatus is critical for testing the different parameters of the network ducts. It includes the evaluation of duct alignment, air tightness, etc.


The purpose of DIT – A brief overview


The Duct Integrity Test resolves to ensure the appropriateness of the duct before the optical fiber cable installation through jetting, blowing, or cable pulling. The prime purpose of DIT is to recognize and determine the suitability of the ducts. It examines if the installed ducts are ready and apt for blowing from one dug hole to another. 


Duct Integrity testing is a critical step before blowing the cables. Why? Because it helps to avoid unseen circumstances and practical challenges. It could be a missing section in the ducts, unsuitable coupling, and blockage in the ducts. The experts carry out the testing process with compressed air, a go-gauge sponge, and a spindle of the correct size. It gets pushed inside from one end with the help of immense pneumatic pressure to throw it outside through the other end. 


Stepwise description of DIT prior to fiber cable blowing - 


First Step - Air pressure check 

Duct continuity is an integral component, and compressed air testing helps determine it. The air gets compressed from one end of the duct. The experts examine if the air comes out through the other end. If there is a blockage and no air comes out, there is a fault. It has to be identified before fiber blowing and rectified before proceeding to the next steps. Duct leakage is also reviewed through compressed air. Here the air is compressed from one unit head to one end of the duct. The testers attach the pressure gauge to one end of the duct to check the leakage. If the pressure drops, it indicates leakage in the duct. 


Second step - The shuttle test

The twists and sharp curves in the installed ducts are convenient to review and locate via shuttle test. A shuttle of an appropriate size gets passed through the duct. It is also done with the help of compressed air. If the shuttle comes out smoothly without barriers from the other end, there is no evidence of blockage. It is then ready for cable blowing. However, if the shuttle does not come out smooth from the other end, it is either kinked or blocked. The testers need to identify the duct blockage and the location of the unwanted kink. They pass a transmitter via the duct and track the blockage point with the help of the receiver. The blocked portion gets replaced, eliminating the fault.


Final step - The sponge test

It is a problem to identify mud and water inside an underground duct. It can create an issue during signal transmission. During the sponge test a sponge with a dimension double the size of the duct's inner diameter gets passed through the duct with the help of compressed air. The purpose is to clean the duct. This way, one can remove the unwanted particles before the fiber cable blows and eliminate the possibility of faults in the duct. 


Pressure test :

Connect one end of the duct to a Pressure Testing Equipment and other end connect an end coupler with a valve where you can measure the pressure with a gauge.Pressurize the duct to 5 Bar and leave it for 30 min. Recommended for a section of 2KM.Pressure drop in 30 min should be less than or equal to 0.5 bar.The amount of pressure drop will determine how much blowing length can be achieved.

What are the critical aspects checked in DIT?


  1. Evaluation of the continuity of the duct
  2. Review and clear the duct to eliminate the particles of mud, stones, or moisture.
  3. Inspect for kinks, blockages in the duct, unwanted sharp bends, etc.
  4. Review the possibilities of leakage in the duct and fix the flaws in the ducts.


The safety aspect – Know it rightly


Duct testing is crucial and following the safety measures is more integral. You must know the safety steps to ensure a hassle-free and effective evaluation before cable blowing. 


  1. Never go inside the pit while the process of duct testing gets conducted.
  2. During the duct evaluation process, do not stand in front of the ducts while blowing air, shutter, sponge, or transmitter.
  3. Take time before releasing the couplers or PTE. It is ideal to wait till the complete release of pressure.
  4. Always use the warning tape for safety with cones while opening the pits.


Closing note – Selection makes the difference


Duct integrity testing is a vital part. You cannot take risks with the steps. Blown fiber technology has become an indispensable choice in the access network installation process. Get a chance to improve the network performance with high-quality equipment pieces and testing steps with the top distributors and manufacturers in the industry. They bring the top equipment pieces and testing solutions to assist professionally. 



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