The savings of Buttonlock in place of Pittsburgh on Low Pressure Rectangular Duct

: Lockformer Company Brochure, August 1968

Snaplock Buttonpunch on Rectangular Duct is making a comeback! Even though Snaplock has been a SMACNA standard for the Longitudinal Seam on Low Pressure Duct since 1969, many shops left it behind in favor one method- Pittsburgh-that covers all duct pressure classes, thereby streamlining their operation with one method on the longitudinal seam as well as saving money and floorspace from having to buy another machine. Buttonlock and Pittsburgh are run on separate machines. The Buttonlock Machine is set up to run the Female Seam “inboard” and the male dimpled Right Angle Flange on the outboard side. It’s a similar operation to the Pittsburgh Lock which has a Female Seam “inboard” and a Right Angle Flange known as the Male Pittsburgh on the other side.

The features that propelled the Buttonlock’s popularity back in 1969 are the same with it’s resurgence today: Labor.

Although the fabrication of the Buttonlock and Pittsburgh are done very similar, it’s in the connection that they differ greatly. With the Buttonlock, the Male Flange can simply be “snapped” into the Female Buttonlock seam. The Pittsburgh Lock however is very labor intensive because once the Male Pittsburgh is mated with the Female Pitts seam there’s a Hammer Over Edge” of the seam that must be Folded Over itself to complete the Lock.

Guys in the field are already used to snapping together round pipe – why not rectangular duct as well? It’s the same process they are used to but instead with rectangular duct instead of round duct.

Rectangular Duct has a length and a width. On completed Duct, the length (referred to as Longitudinal) is seamed; for the Longitudinal Seam there are two options that a Contractor has if the Engineer has specified “per SMACNA”: Buttonlock or Pittsburgh.

Buttonlock can cut assembly time in half vs what’s required in assembling Pittsburgh duct. Fabricated and sent out to job site in 2 piece / L sections “nested” like this below, cutting transportation expenses to job site significantly.

The Buttonlock is SMACNA approved for Low Pressure duct (2” wg and below) and then the stronger Pittsburgh Lock is required for 3” (Medium Pressure) and up.

: Male Buttonlock Seam

: Female Buttonlock Seam

: Buttonlock connection

: Flagler High Speed Button Lock

For Rectangular Duct, what percentage of Snaplock vs. Pittsburgh are you using on the straight duct?

: Snaplock is alternative to Pittsburgh (for low pressure duct) in forming the Longitudinal Seam on Rectangular Duct. Because there’s no hammer over edge, the labor savings is significant.

If 25% or more of a shop’s jobs are low pressure duct (2″ water gauge), the $14,000 investment towards a freestanding Buttonlock machine may be worth the savings that shop would then get in labor both in the shop and in the field. For someone in the field, the option of being able to simply “snap-in” the longitudinal seam would be chosen 100% of the time.

: Lockformer Company Brochure, August 1968

This machine runs a female receiver lock inboard and the male button-punched right angle flange outboard. The inboard female operation is fixed, however the male rolls on the outboard side can be removed and added to another 8 station Rollformer for a crossover setup.