When pressure class changes connector requirements not recognized

Pressure class is not just a label - it can change the required connector, gauge, reinforcement, and sealing method. When duct changes pressure class mid-run, check the joint requirements before sealing or insulating.

Watch out

• Do not assume the same flange setup works after duct size or pressure class changes.

Check

• Find the pressure-class note on the drawing, duct schedule, mechanical notes, or shop drawing for this section.
• Identify where the pressure-class change occurs. Common places include equipment connections, VAV box inlets, distribution mains, branches, or transitions between systems.
• Compare the connector you have installed with what the project spec, approved detail, shop standard, or SMACNA-based table requires for that pressure class.
• Check whether reinforcement, tie rods, cross-angles, gasket, seal class, or a different flange/connector detail is required at the higher pressure section.
• If the wrong connector or reinforcement appears to be installed, flag it before insulating or cover-up. Do not hide a pressure-class mismatch behind sealant or insulation.

Steps

• Find the pressure-class note on the drawing, duct schedule, mechanical notes, or shop drawing for this section.
• Identify where the pressure-class change occurs. Common places include equipment connections, VAV box inlets, distribution mains, branches, or transitions between systems.
• Compare the connector you have installed with what the project spec, approved detail, shop standard, or SMACNA-based table requires for that pressure class.
• Check whether reinforcement, tie rods, cross-angles, gasket, seal class, or a different flange/connector detail is required at the higher pressure section.
• If the wrong connector or reinforcement appears to be installed, flag it before insulating or cover-up. Do not hide a pressure-class mismatch behind sealant or insulation.

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