When designing a loom, a compromise has to be made between contradictory wishes: a big shed that can be opened without much difficulty with a high tension on the warp in a compact loom. The moving breast beam of Louët makes this compromise a lot easier, because with this construction the elasticity of the warp no longer plays a role.
The Louët moving breast beam allows the weaver to treadle a shed with less power. Looking at the diagram below, showing the loom from the side, you will see that a shed is giving the warp a kind of parallelogram shape. Imagine, the warp is made of inelastic material, like metal wire, you will understand that a shed is only possible to make, if the distance between breast beam G and backbeam H becomes smaller.
When this distance is fixed, like on other looms, the power to make a shed depends completely on the elasticity of the warp. When the shed becomes wider, the tension on the yarns increases (enormously, in case of a less elastic warp). That causes heavy treadling and may damage the warp. The moving breast beam solves that problem. It is held by springs, adjustable to give your warp the right tension needed for the weave project.
Besides improvement of the shed and protection of the warp, the springs guarantee exactly the same warp tension each time after you advance the fabric.
Our looms Spring, Delta, Octado and Megado have this moving breast beam system.