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With Zip coupling (YKK High-Strength Zipper)
The zip coupling is the new way of connecting the sections. It is both the most strong and easy way of connection.
It is tested for three years now under high pressures and big diameters (up to 2600mm) at many underground projects with no complain from any mining or tunnel construction company.  
 
  With Steel Ring Connection with multi-clip metal clamps
The one ring inserts into the other and coupling them with metal clamps (following the steps of the photos).
For optimal installation, metal clamps should be installed every 60cm around the circumference of the end rings.
For example, 3 metal clamps are required per section for O400-600mm diameter, 4 for O1000-1220mm diameter.
 
  With Steel Ring Connection with over-cover metal ring
 Each ducting section is manufactured with a steel ring vulcanized in one end of every unit length.
When coupling two ducting units, the end without the steel ring of one ducting is pulled over the steel ring at the end of the other ducting unit.
A coupling clamp is then positioned over the overlapping joint so that the central slot is aligned with the steel ring.  Fastening of the clamp secures the coupling and provides complete airtight sealing.
The over-cover metal ring is manufactured from 1mm thick hot-galvanized steel sheet, specially profiled at a width of 60mm. Tightening of the clamps is provided by a zinc plated threaded crank.