Engineering Manual o.. - HVAC.Amickracing

DAMPER SELECTION AND SIZINGBLADEEDGETHRUSTWASHERBLADESNAP-ON SEAL WORKSWITH COMPRESSIONAND/OR AIR PRESSUREAXLEC2387Fig. 5. Snap-On Blade Edge Seal.SNAP-ON SEAL WORKSWITH OVER-CENTERCOMPRESSIONBEARINGDAMPERFRAMESIDESEALFig. 8. Continuous Spring,Stainless Steel Blade Side Seals.C2389In addition, damper blades can include a reinforcing elementto limit blade torsion or twist (Fig. 9). Depending on the dampersize and sealing requirement, this reinforcement can be on thedrive blade only or on multiple blades. The design of air foil bladesusually increases their torsional stiffness, much like reinforcedstandard blades (Fig. 10). Air foil blades also reduce noise andprovide lower, full open airflow resistance at higher velocities.C2388REINFORCERFig. 6. Over-Center Compression Blade Edge Seal.PRESSUREINFLATESSEALDAMPERBLADEHIGHPRESSURESIDELOWPRESSURESIDEDAMPERBLADEC2386C2396Fig. 9. Reinforced Standard Damper Blade.Fig. 7. Inflatable Blade Edge Seal.Blade side seals minimize leakage between the ends of theblades and the frame (Fig. 8). One type of side seal is a stainlesssteel or coated spring steel spring. Other types of side seals(e.g., molded rubber parts riveted to the frame) conform to theblade cross-section profile when the damper is closed. Bladeedge seals that interfere with blades closing completely couldincrease leakage at blade side seals.The twisting load on damper blades and/or their physical sizemay necessitate heavy-duty or double linkage between blades tominimize torsional bending. Bending of damper blades reducesthe effectiveness of blade edge seals by lowering compressionforces or by preventing complete contact between blades.C2397Fig. 10. Air Foil Type BladeENGINEERING MANUAL OF AUTOMATIC CONTROL423