CSLB C-20 HVAC ContractorPlanning and LayoutMedium
On a mechanical blueprint, a branch duct takeoff is labeled with the symbol 'VD.' What does this symbol most likely indicate?
- AFire damper required by code at a wall penetration
- BVolume damper for manually balancing branch airflow
- CVertical duct riser connecting two floors
- DVane damper integrated into the diffuser face
Show answer & explanationAnswer & explanation
Correct answer: B. Volume damper for manually balancing branch airflow
'VD' is the standard mechanical blueprint abbreviation for a volume damper, a manually adjustable damper installed in a branch duct to balance airflow to individual registers or zones during system commissioning.
Why the other options are wrong
- A. Fire dampers are typically labeled 'FD' and shown at rated wall/floor penetrations.
- C. Vertical risers are shown with directional arrows, not the VD label.
- D. Diffuser-integrated vanes are shown on the register schedule, not labeled VD.
Volume Damper Symbol (VD)
VD on a mechanical blueprint marks a manually operated damper placed in ductwork to balance airflow between branches during system commissioning.
- VD = Volume Damper for balancing
- FD = Fire Damper at rated assemblies
- BD = Backdraft Damper preventing reverse airflow
Memory trick: VD Very Delicately balances the air.