All hose spec sheets will list a bend radius for a given product. For example, a common 2” diameter rubber chemical hose may show a bend radius of 6”. The manufacturer has determined that this hose can be bent into a 6” radius to form a 90 degree or 180 degree turn without damaging the hose. When hoses are very short and turns are tight, the bend radius can be used to determine the minimum length of a given hose assembly.
Calculating the Hose Length
The formula for calculating the bent section of the hose length around a radius is derived from the basic formula that the circumference of a circle = 2πR, where R = the radius of the circle, and π = a constant, = 3.142.
So, if the hose goes around a 90˚ bend, which is 1/4 of a full circumference, and the radius of the bend is R, then the length of the hose around the bend is = 1/4 x 2πR. Or half way round, in a U-shape, = 1/2 x 2πR.
Note: In calculating the length of a hose assembly, the (non-flexible) length of the end fittings must be added in, also the length of any straight sections of hose.
Bend Radius vs hose flexibility
These two terms are related but often cause some confusion. As stated above, the bend radius reflects the minimum possible bend without damaging the product. A 2” rubber chemical hose has a bend radius of 6”, and a 2” composite hose has a 3.5” bend radius. So, the composite hose seems more flexible based on bend radius alone, and that is true. What bend radius leaves out is required force to bend. A composite hose requires 75% less force to bend, so that combined with a tighter bend makes the composite hose much more flexible than the bend radius would suggest.