How do I set the correct counterweight position?

Commission with the system running under representative conditions — ideally with the maximum number of zones closed that would occur in normal operation. Start with the counterweight at a moderate position. If the bypass opens during normal operation, move the counterweight heavier to increase the opening threshold. If the bypass is not opening when noise or VFD hunting is occurring, move it lighter to reduce the threshold. Adjust until the bypass activates only when excess pressure is present and closes cleanly during normal operation. There is no factory-default setting — every installation is different.

Does the HAC-BPD need electrical power or a control signal?

No. The HAC-BPD is entirely mechanical. No wiring, no control signal, no power connection. The counterweight provides the closing force and the setting, the spring provides the closing mechanism, and the duct static pressure provides the opening force. Nothing to wire, nothing to program, nothing to fail electrically.

Can the HAC-BPD be installed vertically — for example in a vertical bypass riser?

Yes. The spring return means the damper can be installed in any orientation — vertical, horizontal, inverted, or at any angle. Gravity-close bypass dampers only work reliably on horizontal duct with the blade hanging downward. The HAC-BPD works reliably regardless of orientation because the closing force is mechanical (spring) rather than gravitational.

What is the difference between the HAC-BPD and the HAC-MBD?

The HAC-BPD opens and closes automatically based on duct static pressure — it is a pressure relief device installed in a bypass branch. The HAC-MBD is set manually to a fixed restriction at commissioning and stays there — it is an airflow balancing device installed in the main duct run. They solve different problems: BPD for dynamic pressure relief, MBD for fixed flow restriction.

Is the HAC-BPD the right solution for a system that is noisy at all grilles even when no zones are closed?

Not directly — if the system is noisy with all zones open, the problem is likely system static pressure at the design condition, not pressure spikes from zone closure. The HAC-BPD is for pressure that builds when zones close. For a system that is noisy at all zones open, the issue is duct design, fan sizing, or grille selection.

HAC-BPD Back Pressure Damper – 24Vac, Spring Return, 4

Product image is representative only. Actual product may differ in appearance depending on size, configuration, and options selected at order.

Spring-return mechanical back pressure damper for automatic duct static pressure relief. Opens when pressure rises above the threshold set by an adjustable counterweight — closes as pressure drops. No wiring. No control signal. No power supply. Mounts any orientation. Available 4"–20" including odd-inch sizes.

Pressure problems this damper solves

→Grille noise when zone dampers close — velocity increases through open zones as static builds; bypass relieves the pressure automatically

→VFD hunting or instability — changing duct conditions as zones open and close cause the drive to chase setpoint; bypass stabilizes the system

→HRV or ERV airflow instability — building pressurization affects HRV/ERV performance; bypass relief in the makeup air circuit stabilizes the unit

→Pressure spikes causing nuisance trips — safeties or high-limit switches triggering on pressure events; bypass prevents the spike from reaching trip threshold

✓ Spring return — mounts any orientation — vertical, horizontal, inverted, or any angle; closing force is mechanical, not gravitational; installs wherever the bypass duct needs to go

✓ Adjustable counterweight sets the opening threshold — set at commissioning with the system running; heavier = higher pressure required to open, lighter = more responsive

✓ No wiring, no controls, nothing to fail electrically — purely mechanical; responds to duct conditions automatically for the service life of the installation

✓ Foam rubber sealed — tighter leakage control than unsealed bypass dampers; closes cleanly during normal operation so the bypass doesn't become a continuous air leak

✓ 4"–20" including odd-inch sizes — matches bypass duct diameter exactly; square and rectangular configurations available as special orders — contact factory

HAC-BPD — use for pressure relief

✓Opens and closes automatically based on duct static pressure

✓Responds dynamically — active only when pressure rises

✓System protection — relieves excess pressure, closes when normal

✓Install in bypass branch — not in main duct run

HAC-MBD — use for fixed restriction

→Set manually at commissioning — stays at that position

→Does not respond to pressure changes — fixed position only

→Airflow balancing — trims a specific flow rate and holds it

→Install in supply, return, or fresh air duct run

Size	Part Number	Configuration
4"	HAC-0400-BPD	Spring return, adjustable counterweight, foam sealed
5"	HAC-0500-BPD	Spring return, adjustable counterweight, foam sealed
6"	HAC-0600-BPD	Spring return, adjustable counterweight, foam sealed
7"	HAC-0700-BPD	Spring return, adjustable counterweight, foam sealed
8"	HAC-0800-BPD	Spring return, adjustable counterweight, foam sealed
10"	HAC-1000-BPD	Spring return, adjustable counterweight, foam sealed
12"	HAC-1200-BPD	Spring return, adjustable counterweight, foam sealed
14"	HAC-1400-BPD	Spring return, adjustable counterweight, foam sealed
16"	HAC-1600-BPD	Spring return, adjustable counterweight, foam sealed
18"	HAC-1800-BPD	Spring return, adjustable counterweight, foam sealed
20"	HAC-2000-BPD	Spring return, adjustable counterweight, foam sealed

Select diameter only — all units identical in configuration. 9" is not available in this series. Square and rectangular configurations available as factory special orders.

Operation

Automatic — no wiring, no controls

Sizes

4"–20" incl. odd inches

Fail-Safe

Spring return — any orientation

Threshold Setting

Adjustable counterweight — set at commissioning

Seal

Foam rubber — low leakage when closed

Warranty

10-year mechanical

Commission with the system running. There is no factory-default counterweight setting that works for all applications. Set the counterweight with the maximum number of zones closed that would occur in normal operation. If the bypass opens during normal operation, move the counterweight heavier. If it isn't opening when noise or VFD hunting is occurring, move it lighter. Adjust until the bypass activates only when excess pressure is present and closes cleanly during normal operation. Need help sizing the bypass branch? Contact 1-800-661-7382.

10-year mechanical warranty

Made in Canada · No wiring, no controls, nothing to fail electrically

HAC-BPD Back Pressure Damper — Automatic Pressure Relief, No Power Required, 4"–20"

Description

HAC-BPD Back Pressure Damper — Automatic Pressure Relief, No Power Required, 4"–20"