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| Actuator |
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| A mechanical accessory item attached to a damper to move its blade(s) to either the open or closed position, or to an intermediate position for flow modulation. Actuators may be manually, electrically, pneumatically or hydraulically powered. |
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| Actuator Torque |
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| The maximum rated torque capacity of a rotary output actuator. |
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| Adjustable Louver |
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| A louver in which the blades may be operated either manually or by mechanical means. |
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| Airfoil |
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| A double skinned blade whose skins meet at the leading and trailing edges with no substantial external protrusion(s). |
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| Air Pressure |
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| Psr and Pyr are gauge pressures measured by a manometer or other pressure measuring device connected to a Pitot tube or to pressure taps. |
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| Backdraft Damper |
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| A backdraft damper is a device which, when mounted in a duct or opening, permits the flow of air in one direction only. It is normally opened by the energy of the air stream but may be opened and/or closed by mechanical means. A counterbalanced backdraft damper has weights and/or springs added to the blade or blades to facilitate or impede the opening or closing action. |
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| Barometric Pressure |
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| Barometric pressure is the absolute pressure exerted by the atmosphere. |
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| Bearing |
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| Each blade axle rides in a bearing at the damper frame. The bearing may be a sleeve bushing or ball bearing. While normally pressed into the frame, they may be die formed in the frame member. If the blade axles are vertical, a thrust bearing or washer may be used on the lower axle to keep the blade end from rubbing on the frame or blade seal. |
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| Blade |
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| The positionable closure element in a damper. |
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| Blade Axle |
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| A blade axle Is a shaft that extends from the blade through the frame providing for blade rotation. A blade axle may be mechanically fastened, welded or riveted to each end of the blade. One shaft is made longer than the others to allow for external actuation of the damper. |
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| Blade (Edge) Seal |
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| An edge seal is a strip of material applied at the blade edge to reduce leakage between adjacent blades, and between a blade's edge and its stop. |
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| Blade Stop |
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| A blade stop is a rigid strip located on the top and bottom frame members to provide a positive halt of blade rotation in the closed position and to minimize air leakage at these locations. A blade stop is usually metal and is fastened in place, or may be incorporated in the damper frame. |
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| Blade Support |
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| A structural member inside the duct section of a guillotine damper frame which supports a portion of the closed blade load. |
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| Ceiling Damper |
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| A ceiling damper is a device to protect openings in a fire-rated horizontal ceiling assembly which operates to interrupt airflow automatically in the event of a fire so as to restrict the passage of flame and heat. |
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| Chain Drive |
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| A chain arrangement used in conjunction with sprockets to transmit reversible rotary actuator force to a guillotine blade. Also: A link-chain loop used with a chainwheel to permit manual rotation of a manually-turned actuator input shaft from a convenient lower lever. |
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| Damper |
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| A mechanical assembly placed into a duct or opening, which may be actuated on command to isolate or regulate gas flow. |
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| Fire Damper |
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| A fire damper is a device arranged to interrupt airflow automatically through part of an air system so as to restrict the passage of flame, and is installed in a fire-rated wall or floor to close automatically in the event of a fire so as to restrict the passage of flame and heat. |
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| Fixed Louver |
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| A louver in which the blades do not move. |
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| Flow Distribution |
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| The pattern of variation of gas flow in ductwork, usually expressed in terms of variation of gas velocity across a representative duct cross-sectional area. |
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| Isolation Damper |
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| A damper whose primary function is to restrict or prevent gas leakage when closed. |
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| Leakage |
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| The volume of duct gases which can pass through a closed damper at a given set of conditions. Usually expressed as Actual Cubic Feet per Minute (ACFM), Pounds per Hour, Percentage of Normal Flow Rate or Percentage of Maximum Flow Rate. |
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| Leakage Area |
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| The total area of various flow paths between component parts of a fully closed damper. |
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| Linkage |
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| Linkage is the mechanism which connects damper blades for actuation purposes. The mechanism may be mounted on the blade faces or concealed within the damper frame, and Is normally installed, tested and fixed in position at the factory. |
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| Louver |
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| A louver is a device comprising multiple blades which, when mounted in an opening, permits the flow of air but inhibits the entrance of other elements. |
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| Modulate |
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| To vary flow rate and/or pressure drop by changing the restriction to flow in response to an input signal. Effect of damper closure positioning to vary flue gas flow rate, flow velocity or pressure; the action of damper and damper controls to maintain a pre-set series of flow parameters such as pressure or temperature. |
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| Mullion |
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| A mullion is a division between multiple section dampers. The typical mullion will inherently add stiffnessas it is constructed of two jambs fastened together with or without reinforcement. |
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| Normal Operating Conditions |
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| The pressure and temperature range at the damper when the system in which the damper is installed is functioning within the planned productive operating range and conditions. |
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| Opposed Blade Damper |
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| A damper in which adjacent blades rotate in the opposite direction. |
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| Parallel Blade Damper |
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| A damper in which the blades rotate in the same direction. |
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| Penthouse |
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| A penthouse is a roofed structure incorporating louvers or louver blades in all or part of the walls and usually designed to be installed on the roof of a building. |
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| Pressure |
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| Pressure is force per unit area. This corresponds to energy per unit volume of fluid. |
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| Pressure Drop |
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| The pressure loss which is added to system pressure loss, due to the presence of the damper. |
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| Seals |
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| Components which are located on a damper blade or frame to limit the leakage areas between mating surfaces of a closed damper. |
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| Shut-Off Damper |
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| A damper whose function is to be either fully-open or fully-closed sometimes called "on-off" service. The expression does not necessarily connote flow isolation. |
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| Shaft |
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| In louver dampers the supporting structural element in the blade through which rotary motion produces blade relocation. In guillotine dampers a bar or tube through which actuator rotation is transmitted between drive members. |
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| Side (end or jamb) Seal |
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| A side seal is a strip of material positioned between the damper frame and the end of a blade to reduce undesirable leakage of air between the blade and the damper frame. |
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| Smoke Damper |
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| A smoke damper is a damper intended: (1) to restrict the spread of smoke in HVAC systems that are designed to be automatically shut down in the event of a fire or (2) to control the movement of smoke within a building when the HVAC system is operational in engineered smoke control systems. |
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| Static Pressure (Pv) |
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| Static pressure is the normal force per unit area at a small hole in the wall of a duct or other boundary surface. The wall and boundary surfaces must be parallel to the gas stream and so located that velocity will have no effect on the measurement. It exists by virtue of the gas density and degree of compression alone. |
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| Stub Shafts |
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| Short, non-continuous shafts that penetrate through the linkage, bearing, packing box, frame and into the blade of a louver or butterfly damper. |
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| Stuffing Box |
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| A dimensionally-controlled chamber surrounding a shaft penetration into a damper frame into which packing may be installed to seal around the shaft. |
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| Velocity Pressure (Pv) |
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| Velocity pressure is the force per unit area capable of causing an equivalent velocity in a moving fluid. It exists by virtue of the gas density and velocity alone. |
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| Volume Control Damper |
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| A volume control damper is a device which, when mounted in a duct or opening, is used to vary the volume of air flowing through the duct or opening. It may be operated manually or mechanically and may have one or more blades. |
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