Flow liners must be designed such that they allow the ducts to move axially and laterally during operation. We differentiate between cylindrical, conical, and telescopic flow liners. The tube thickness of the flow liner is between 3 and 5 mm, depending on the duct dimensions and anticipated abrasion. For flange expansion joints, the flow liner is pushed into the installation gap along with the expansion joint, whereby an additional seal should be provided between the duct and flow liner flange.

For expansion joints with construction angles, the flow liners are usually welded on. In some cases, the expansion joint will need to be designed with an installation seam. 

In order to protect the pre-insulation layer from dust accumulation in expansion joints with construction angles, a swimming flow liner or sliding plate has proven to be of value when guided on one side with a retaining plate on the construction angle, such that it permits duct movements in all directions.

In the event of media flow from the bottom up in vertical or inclined lines, they are installed against the media flow. A bend is welded to the inside of the duct before the open end of the flow liner, which will then conduct the medium past the flow liner opening. Deposits of solid matter between the expansion joint and flow liner are thus avoided.