Type : Motorized Smoke Damper
Leakage Rating :Class -III
Blade Type : 3V Single Skin; A : Parallel Operation
Construction : Galvanized Steel (GI)

MSD B-21 Series is a high performance UL 555S Classified smoke damper with Class-III leakage rating, installed vertically or horizontally (with blades running horizontally) and is rated for airflow and leakage in either direction.


UL- 555 Test Ratings

Leakage Rating : Class -III

Max Velocity : 2000 fpm

Max Operating Pressure: 4 in. w.g (1000 pa)

Operating Temperature : 250°F (121°C) for ½ hr- Class-II
350°F (176°C) for ½ hr – Class-III

Additional Test Ratings

Operating Temperature :250°C (482 °F) for 1 hr* (HKFSD)
:250°C (482 °F) for 2 hr* (HKFSD)

Standard Construction


16 gauge (1.4 mm – 1.7 mm) thick galvanized steel


Parallel operated 3 ‘V’ type blade made of 16 gauge (1.4 mm – 1.7 mm) thick galvanized steel.

Blade Seals

Silicon rubber blade seals.

Jamb Seals

Stainless steel.

Jack Shaft

12 mm diameter Galvanized steel shaft.


Honeywell, Belimo, Seimens (24V AC, 120V AC, 230V AC).


Minimum 0.9 mm, single section is field or factory installed.
Multiple section is factory installed.
Sleeve thickness as per NFPA table 3-4.6.3.

Limit Switches

For BMS open / close indication.

Optional Fittings

Retaining Angles

1½” x 1½” x 16 gauge (40 x 40 x1.5) mm.

Thermal Response Device (TRD)



Externally mounted open, close visible Indicator.

Push Button

For manual reset of damper.

Transitions (R)

Neck adapter for round duct connections.

Junction Box

Smoke Detector

Model : MSD-GB-21C3-A/R UL 555S Damper meetsthe required standards of SMACNA, NFPA, IBC, BOCA, ICBO, UL.

Actuator location standard: Left side from rear view
(Jack shaft view)

Note :
FC : Fail Close in the event of Fire
FO : Fail Open in the event of Fire

* The temperature ratings are for Honeywell 20 Nm actuators
with thermal enclosures.

Optional Construction (UL Certification N/A)

Frame : Stainless Steel 16 gauge (304/316L)

Blade : Stainless Steel 16 gauge (304/316L)


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