ACCESSORIES

Equipment often purchased by the manufacturers to be mounted on the damper to enhance its applicability.  Accessory items include actuators, seal air systems, limit switches, flow control sensing and positioning equipment, and other equipment associated with drives, sensing and signaling.

ACTUATOR

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.

ACTUATOR TORQUE

The maximum rated torque capacity of a rotary output actuator.

AIRFOIL

A double skinned blade whose skins meet at the leading and trailing edges with no substantial external protrusion(s). Generally fabricated with internal support members and skins constructed of metal plates.

AREA OF RESTRICTION

The total area of any items (measured at right angles to the directions of flow and when the damper is fully open), which are permanently located in the gas path.

BLADE

The components of a damper that may be moved to allow gas flow, shut off gas flow, or regulate gas flow to a duct or item of equipment.

BLADE ENTRY SEAL

The sealing arrangement on a guillotine damper through which the blade traverses. 

BLADE STOP

A barrier attached to the damper that restricts further motion of the damper blade to prevent damage to damper seals or drive systems.

BYPASS

A duct which may be opened or closed to permit flow to be diverted around system equipment for emergency operation, reheat, or other operating condition.

BLADE SUPPORT

A structural member inside the duct section of a guillotine damper frame that supports a portion of the closed blade load.

BLANKING PLATE

A manually installed isolation device that is temporarily installed in the ductwork to shut off flow to ducts or equipment, which require long-term isolation of maintenance.

BONNET, OPEN

The portion of a guillotine damper frame that houses the blade in the fully open position.  Allows leakage to or from atmosphere.

BONNET, FULLY ENCLOSED

The enclosed portion of a guillotine damper frame that houses the blade in the fully open position.  Prevents leakage to or from the atmosphere

BONNET, SEALED

See BONNET, FULLY ENCLOSED.

BUTTERFLY DAMPER

A single blade louver damper.  Usually round, and made with flat plate blade.

CONTROL DAMPER

A damper designed to regulate or control one of more flow parameters such as pressure drop, rate of flow or flow distribution.

CHAIN & SPROCKET DRIVE

See CHAIN DRIVE.

CHAIN DRIVE

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 chain wheel to permit manual rotation of a manually turned actuator input shaft from a convenient lower level.

DAMPER

A mechanical assembly placed into a duct or opening, which may be actuated on command to isolate or regulate gas flow.

DOUBLE -BLADE GUILLOTINE

See GUILLOTINE, DOUBLE-BLADE

DOUBLE LOUVER DAMPER

A louver damper consisting of two sets or stages of blades in series with an interstage volume pressurized by a seal air blower to prevent flue gas leakage through the closed damper.

DRAW

The blade movement direction of a guillotine damper.  For horizontal ducts, the damper may be configured to permit blade opening and closing from the top, bottom, or side. This is known as top draw, bottom draw and side draw respectively.  For vertical ducts, flat draw entry may be used.

DRIVE

See ACTUATOR

DRIVE LIFTING FORCE

The tensile force required to move a guillotine blade under specified conditions.

DRIVE SYSTEM

The actuator and all components through which forces are transmitted to the blade for the purpose of positioning the blade.

DUAL LOUVER DAMPER

See DOUBLE LOUVER DAMPER. 

ENTRY DOOR

An entry closure device for guillotine dampers that have blades that cannot be withdrawn through entry seals.  Entry doors close over the blade entry opening after the damper blade is opened or closed to restrict leakage.

FLOW DISTRIBUTION

The pattern of variation of the gas flow ductwork, usually expressed in terms of variation of gas velocity across a representative duct cross-sectional area.

FRAME

The external damper assembly that supports the blade(s) and includes duct-attachment means, with provision for attaching actuators and other accessories a required.

FREE AREA

The internal cross-sectional area of the duct portion of a damper, less the area of restriction. 

GOGGLE VALVE

A damper whose blade contains a solid duct closure and an extended portion of blade having a cutout sections which matches the duct inside dimensions.  The damper is arranged so that either the open or closed blade section may be inserted into the main frame which is attached to the duct; leaving the unused part of the blade projecting outside the frame.  The name was first applied to a "goggle-shape" blade that had been designed for round ducts.  The name is now also applied to such dampers when used with other duct shapes.

GUILLOTINE DAMPER

An isolation damper having blade(s) that are withdrawn from the duct area when the damper is fully open.

GUILLOTINE, DOUBLE-BLADE

A guillotine damper with two parallel blades.  The volume between blades can be pressurized with a seal air system to prevent flue gas leakage pass the blades.

HEIGHT

Used as a dimensional reference to damper size.  In a guillotine damper, the duct inside dimension which is parallel to the directions of blade draw; in a louver damper, the duct inside dimension which is perpendicular to the shaft axis.

ISOLATION

The restriction of gas flow.  The extent to which leakage is restricted varies with application requirements, the damper construction and design, and capital cost of the damper.

ISOLATION DAMPER

A damper whose primary function is to restrict or prevent gas leakage when closed.

ISOLATION, MAN-SAFE

An isolation damper system to seal off flue gases so that men without breathing apparatus or other special equipment may safely perform maintenance activities in the isolated section.

LEAKAGE

The volume of duct gases that 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.

LEAKAGE AREA

The total area of various flow paths between components parts of a fully closed damper.

LEAKAGE, ZERO

A condition in which no flue gas passes through a closed damper to the duct area downstream of the damper.  (Note: If a seal air system is used, it should be anticipated that the seal air will leak into the downstream area.)

LINKAGE

The lever arms and connecting bar assemblies that can be driven by a single actuator to produce the correct mechanical motion of the blades in a multiple-blade louver.

LOAD BAR

See BLADE SUPPORT.

LOUVER DAMPER

A damper with one or more blades that rotate and remain in the gas stream. 

MODULATE

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. 

OPERATING CONDITIONS

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.  Also known as the Normal Operating Conditions.

OPERATOR

See ACTUATOR.

PACKING

Sealing materials contained in stuffing boxes for the purpose of minimizing or eliminating leakage at shaft penetrations through the damper frame.

PERIMETER AIR SEALED

A guillotine damper whose frame design includes a chamber around the duct into which the blade(s) may enter, and into which seal air may be introduced. 

PRESSURE DROP

The pressure loss that is added to system pressure loss, due to the presence of the damper.

RACK AND PINION

A blade actuating system in which rotary effort to a toothed wheel causes linear motion of a mating bar with compatible tooth forms. 

RACKING

Twisting of a damper frame out of its intended planar arrangement.

SALES SLIP

The difference between what sales told the customer and what can be actually done in this, the real, world.

SCREWJACK

A guillotine damper blade drive mechanism that uses a screw concept to change actuator rotation to linear movement.

SEALS

Components that are located on a damper blade or frame to limit the leakage areas between mating surfaces of a closed damper.

SEAL AIR

Ambient air that is introduced into the sealing chambers of a damper at higher pressure than the duct gases thus providing a barrier to the passage of the duct gases.

SEAL AIR CHAMBER

An air pressurized volume on a guillotine damper that encompasses the edge of the damper blade and seals the blade entry opening to prevent flue gas leakage.  On a double louver it is the pressurized volume between two (2) rows of blades.

SHAFT

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 the actuator rotation is transmitted between drive members.

SHUT-OFF DAMPER

A damper whose function is to either fully open or fully close, sometimes called "on-off" service.  The expression does not necessarily connote flow isolation.

SLIDE GATE DAMPER

See GUILLOTINE DAMPER.

STUB SHAFTS

Short, non-continuous shafts that penetrate through the linkage, bearings, packing box, frame and into the blade of a louver or butterfly damper.

STUFFING BOX

A dimensionally controlled chamber surrounding a shaft penetration into a damper frame into which packing may be installed to seal the shaft.

SPROCKET

A gear-like disc whose teeth are shaped to mate with a drive chain to convert actuator drive rotation into tensile forces on a chain.  Used to position a guillotine blade.

THROAT SEAL

A blade entry seal.

TWO STAGE LOUVER DAMPER

See DOUBLE LOUVER

UPSET CONDITIONS

Recognized potential excursions of pressure and/or temperature beyond the normal operating range usually for short periods. The damper must either survive the upset conditions without subsequent inhibition of normal damper function, or the damper must perform specified functions in these conditions.

WEATHER COVER

A non-gas-tight enclosure on a guillotine damper which protects damper drive components from ice formation or other exposure but which does not prevent leakage to or from ambient.

WET/DRY INTERFACE

A location in ductwork that is exposed to alternating wet and dry conditions.  Such locations are likely to be subject to deposition, collection, and concentration of corrosive materials.

WIDTH

Used as a dimensional reference to damper size.  In guillotine damper, the duct inside dimension which is perpendicular to the direction of the blade draw; in a louver damper, the duct inside dimension which is parallel to the shaft axis.

WIRE CABLE

A tensile force component consisting of strands of metal wire that may be used to position a guillotine damper blade. 

WIRE CABLE SHEAVE

A grooved wheel used in conjunction with a wire cable to convert actuator drive rotation to tensile force on a cable that can reposition a guillotine damper blade. 

ZERO LEAKAGE DAMPER

A term generally used to describe a damper that prevents flue gas leakage to isolated equipment or ductwork.  The damper may use seal air to prevent flue gas leakage.