Directional Movement for Fabric Expansion Joints
Axial Compression
The reduction in the breach opening along the axis of the duct. This is usually a result of thermal expansion of the ducting.
Axial Extension
The increase in the breach opening along the axis of the duct. In certain configurations, the duct thermal expansion may result in extension at the expansion joint location.
Lateral Movement
The relative movement of the upstream and downstream faces in the direction perpendicular to the axis of the duct.
Torsional Rotation
The twisting of one side of the duct about the longitudinal axis.
Angular Rotation
The twisting of one side of the duct about an axis perpendicular to the longitudinal axis.
Fabric Expansion Joint Movement Chart
 
The chart shown above depicts the relationship of belt span, maximum compression and concurrent lateral movements. The maximum compression is a percentage of the available belt span (shown as the right end of the plot line). The wider the span, the more capacity for compression. The lateral capacity is a function of the belt slack created with concurrent compression.
As the compression increases, more belt material is available to safely allow movement without overstressing the fabric material. In situations with large lateral movement and little compression, the joint can be installed pre-compressed to have more lateral capacity.
When in doubt, allow experienced U.S. Bellows engineers to help select the correct span for each particular application.
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