Sheet Metal and Fabrication Flashcards
7 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Sheet Metal and Fabrication flashcards as text
What does the term 'duct aspect ratio' refer to, and why does it matter?
Answer: The ratio of duct width to height; high ratios increase friction loss
Aspect ratio is the width-to-height ratio of rectangular duct; ratios above 4:1 significantly increase friction losses and material use.
When fabricating a conical reducer in round ductwork, what maximum taper angle minimizes turbulence?
Answer: 15 degrees or less per side
Keeping the taper angle to 15 degrees or less per side (30 degrees total included angle) minimizes flow separation and turbulence in a conical reducer.
What is a 'snap lock' seam used for in HVAC sheet metal fabrication?
Answer: Joining round duct spiral seam longitudinally
The snap lock seam is the longitudinal seam used on spiral wound round duct, formed continuously by interlocking the strip edges as it is wound.
Which material is NOT typically acceptable for use as HVAC duct in a commercial building per IMC/SMACNA?
Answer: PVC plastic
PVC plastic duct is generally not acceptable for supply and return HVAC systems in commercial buildings due to flammability concerns, though it may be allowed for specific exhaust applications.
A duct system tested at 1.0 inch WC positive pressure is classified under SMACNA as what pressure class?
Answer: 1-inch WC (low pressure)
SMACNA classifies duct systems tested at 1.0 inch WC as the 1-inch pressure class, requiring specific gauge and reinforcement standards.
When cutting galvanized sheet metal with power shears, what safety practice is most critical?
Answer: Wearing cut-resistant gloves and eye protection to guard against sharp edges and metal fragments
Cut-resistant gloves and eye protection are essential when using power shears because edges are razor-sharp and metal chips can become airborne projectiles.
What is the purpose of a turning vane inside a rectangular duct elbow?
Answer: Reduce pressure drop by guiding airflow smoothly around the bend
Turning vanes guide air smoothly around sharp radius elbows, significantly reducing the static pressure loss associated with abrupt direction changes.