Flutter: The repetitive oscillating movement of the Operating Pressure: The pressure or vacuum condition
expansion joint material due to fluctuation between which occurs during normal performance.
positive pressure and negative pressure or due to flow
induced pulsations. This phenomenon is detrimental to Operating Temperature: The gas temperature at which
expansion joints. the system generally will operate during normal
conditions.
Frame: The complete angle iron or plate frame to which
belt or bellows portion of the expansion joint is attached. Pre-Compression: Compressing the expansion joint
(shortening the manufactured F/F) so that in the cold
Flow Deflector: A metal baffle installed in the ductwork position the joint has a given amount of compression
adjacent to the expansion joint, that diverts the gas set into the joint. The purpose of pre-compression is
stream over the flow liner for the purpose of preventing to allow for unexpected or additional axial extension
the particulate in the flow stream for entering the and/or lateral movement.
expansion joint cavity. It also can be used to prevent
condensation from entering the expansion joint cavity. Pre-Set: Dimension that joints are deflected to insure
that desired movements will take place. See lateral offset
Gas Seal: The layer or specific ply of the expansion and manufactured F/F.
joint material that is designed to minimize or contain
the flue gas. Resultant Movement: The net effect of concurrent
movements.
Lateral Movement: The relating displacement of the two
ends or the expansion joint perpendicular to its Set Back (Stand Off Height): The distance the
longitudinal axis. The displacement movement usually expansion joint is set back from gas stream to allow for
caused by the thermal expansion of the ducting system lateral movement and to prevent the joint from
and measured in inches or millimeters. protruding into the gas flow.
Lateral Offset: The offset distance between two adjacent Shipping Bars: Braces that are located between the two
duct flanges or faces. Can be due to misalignment or, by expansion joint flanges to prevent over-compression or
design, to compensate for excessive displacement in the distortion during shipment and joint assembly or
opposite direction during cycling. (Cold lateral offset) installation. These braces must be removed after
installation.
Lifting Lugs: A lifting device that is attached to the
metal portion of the expansion joint for field handling Splice: Procedure for making endless boot or bellows
and erection. from open ended material. Splicing may be accomplished
by one or more of the following: cementing, bonding,
Manufactured F/F (Face to Face): The manufactured heat sealing, stitching, vulcanizing or mechanical
width of the joint measured between joint flange faces. fastening.
The joint may be set into a breach opening that is less
than the manufactured F/F of the joint to allow for axial Telescoping Liners (Overlapping Liners): Metal shields
extension. attached to each side of the expansion joint, that overlap
or telescope together under thermal movements.
Misalignment (Offset): The out of line condition that
exists between the adjacent faces of the breach or duct Thermal Barrier: A layer of insulating material designed
flanges during ductwork assembly. to reduce the surface temperature at the gas sealing layer
to a level compatible with its heat resistance capability.
Molded Corner Expansion Joint: A rectangular
integrally flanged expansion joint in which the corner Weld-In Liner: A liner that is designed to be welded to
is molded to form a continuous unspliced section. the existing duct wall. This design can be either single
or telescoping type.
Movements: The dimensional changes which the
expansion joint is required to absorb, such as those
resulting from thermal expansion or contraction.
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