Duct Connections & Sealing
TDC connections, standing drive slips, duct sealant classes, seal classifications, hanger spacing, and flexible connectors.
- Describe TDC, drive slip, and companion flange connection methods
- Apply SMACNA duct sealing standards and seal classifications
- Specify reinforcement, hanger types, and support spacing
Lección 1
TDC, Drive Slips & Connection Methods
TDC (Transverse Duct Connection)
The TDC (transverse duct connection) flange is the most widely used connection method for rectangular duct in North America. A rolled flange is formed on each end of the duct section. The two flanges are bolted together with a corner piece (90-degree bracket) at each corner and a gasket between the flanges.
Drive Slip Connection
A drive slip (also called S-slip or standing drive slip) connects two duct sections by sliding a formed metal strip over the raw duct edges. The slip has a pocket on each side that captures each duct edge. Button punches or sheet metal screws lock the slip in place. Drive slips are faster than TDC but limited to smaller duct sizes and lower pressures.
Companion Flange (Angle Flange)
A companion flange (angle iron flange) is riveted or welded to the duct end. Two flanges are bolted together with gaskets. This method is used for large, high-pressure duct where TDC flanges are insufficient. The angle iron provides superior structural support at the connection.
TDC Flange
Speed: Fast - machine-formed
Pressure: Up to 4" w.g.
Duct size: Up to 84"
Seal: Gasket between flanges
Drive Slip
Speed: Fastest connection
Pressure: Low pressure only
Duct size: Up to 48" typically
Seal: Sealant required
Companion Flange
Speed: Slow - custom fabrication
Pressure: High pressure, 6"+ w.g.
Duct size: Any size
Seal: Gasket with bolted flange
TDC flanges are the most common rectangular duct connection, using machine-rolled flanges with corner brackets and gaskets. Drive slips are fastest but limited to smaller, low-pressure duct. Companion flanges handle large, high-pressure applications.