DESCRIPTION OF A CONSTANT SUPPORT HANGER
Constant support hangers are used to support structures and components (e.g. pipes, vessels, etc.) that experience vertical movement. The constant hangers provide support at critical locations of a structure such that the temperature dependent deformation of the structure does not produce any excess stress in the structural system.
Theoretically, a constant support provides a constant force on the structure so that it does not experience any extra resisting forces from the support. However, in reality, complete constant load reaction is not possible. That is why the MSS standard allows a maximum tolerance of 6% of the constant load throughout the entire travel range.
Constant resistance to a moving load is achieved by balancing the moment of the moving structure by the moment produced by the force of a compressing/decompressing spring about a common pivot point.
The movement of the constant hanger rod, supporting a load, is animated in the video clip. As the hanger rod connected to the cam moves down (or up) on the left hand side, the spring on the right hand side is compressed (or decompressed) by the spring rod.
Here, the moment of the external load acting downward along the hanger rod varies as the supporting pipe moves (down or up). The variations of the moment (due to changing moment arm length) of the moving external constant force is balanced by compressing (or decompressing) the spring with the lever arm about the same pivot point.
In designing a constant support hanger, minimum variation of the load is optimized via selecting the proper arm lengths of the external force and the spring force, and the spring constant for a given total displacement of the external load.