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1. Please explain the different joining methods? 

  • There are basically three joining methods. Flanged, Welded and Clamp-together Duct (CTD). Within Flanged there are three variations. 
  • Flanged - All Flanged duct uses mating flanges also known as Angle Rings, or simply ‘rings’. These flanges/rings (term used inter-changeably) are typically carbon steel or stainless angle iron that is rolled and then the ends are welded so that the resulting ‘ring’ fits over the duct. A bolt hole of various patterns is punched into the ring. Specification for the holes is usually bolt size, bolt hole center and with either standard configuration or Chicago style hole pattern. (Chicago- has additional holes) The carbon steel rings are sometimes galvanized by plating or painted for protection.
    • Vanstone or Welded Duct
      1. Vanstone - If the duct is to be Vanstoned, this means that a 90 degree lip is turned onto the duct after the ring is in place. The loose flanges of the mating pieces then pull the sandwiched vanstoned ends together in a pressing motion as the bolts are tightened. This is also known as loose flange application as the flanges are not attached to the duct. 
      2. Welded - In this case the flanges are welded to the duct with either a specified full weld or skip weld/interval welding. The mating flanges are then pulled together and mate to one another.
  • Clamp Together Duct (CTD) simply uses an over center latching clamp to tightly ‘draw’ and join the rolled lips that are preformed onto the duct. This is similar in a smaller fashion to the lips and clamping of a 55 gallon metal drum. A sealing gasket secured in the clamp insure that the joint is tight.  Visit our Clamp Together Duct FAQs page for more info.
  • Welded Duct - The ends of this duct are raw (un-formed) and are simply welded together. 

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2. What are the advantages of Vanstone over Welded? 

  • Actually it is most often a case of preference, need and application. For example, flanged duct is often thought to be for applications too heavy for Clamp Together Duct. But as CTD is now available in heavy gauge that idea is often challenged. However, since CTD is only available up to 24”, of course flanges or welding is the only alternative for these large sizes.
  • Welding is the least common method of joining and is primarily reserved for applications where it must be 100% (no room for error whatsoever) air or liquid tight. It is of course permanent and costly.
  • Flanged duct work can be sealed very tightly with the addition of a gasket between the mating flanges. However, it typically takes a skilled mechanic to cut to length and fit the flanges- either by vanstoning or welding. There is minimal room for error. 
  • CTD on the other hand is adjustable. US Duct, more so than others, has the ability to utilize infinite length adjustment in each fitting. (See clamp together duct adjustability) It is the adjustability and clamping that makes it the choice for those who want the fastest installation or who lack the skill to fit and/or weld. 

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3. What if I don’t know what I need?

  • Many of our customers don’t know the details and specifics they need and a lot of the others just want us to do the details for them. So give us a call. Typically, all we need is a rough idea of where you want to collect from and collect to and the location and port size of your equipment. General information about the product also helps. We can get started from there and work it through with you. Once we have the basics, we can do a GoToMeeting to look at the layout and discuss the duct requirements. It really is just like us being there with you.

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3. What about your Clamp Together Duct?



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