Sudbury International Engineered Products Limited carries metal hoses by Hose Master. A recent blog entry by the manufacturer discusses minimum bend radius, or MBR, an important measure of flexibility. Many users misunderstand the method of measuring MBR. Most hose constructions list one MBR, but corrugated metal hoses list two: a static and dynamic one. There are significant differences between these two kinds of MBR and how they should be used.
Measured to the centre line
The Association for Hose and Accessories Distribution defines a static MBR as the smallest radius at which a hose can be used without kinking while bent or flexed into a fixed position. It defines a dynamic MBR as the smallest radius at which the hose can be used while kinking during continuous flexing. Regarding corrugated metal hoses from Sudbury International, users typically measure the MBR to the centre line of the hose.
Some refer to hose dynamics as the constant or intermittent flexing of an assembly, but other application variables should be classified as dynamics, since they can affect assembly cycle life. Examples of dynamics include flexing or bending the assembly, vibration, and large pressure swings. If a user encounters severe dynamic pressures, additional derating factors should be applied to protect the corrugations from these extreme dynamics.
Since most hose applications include dynamics, it is not usually okay to install a metal hose at its static MBR. Static applications typically occur in installations in which there is some offset in the piping system that is easier to accommodate by using a flexible hoses instead of pipe fittings. The hose is easier to install, and there are fewer connection points.
Hose Master recommends installing a Sudbury International corrugated metal hose in as gentle of a bend as possible, even in static applications. If that is unfeasible, it is vital to understand the allowable radius at which the hose can be installed. Knowing the installed radius in an application enables the use of hose-length calculation formulas to make sure there is enough hose in the assembly to accommodate offsets or movement.
For more information, contact Sudbury International.