Before we proceed it's important to note that minimum bend radius is not how far you can bend a hose physically. Depending on strength, stature, or arm-wrestling record, one may be able to bend the toughest six-wire hose into a pretzel, while those of us with non-herculean strength struggle to fit a two-foot section into a box. In the former case however, our Hercules would be at a severe disadvantage as he's bent his hose past the minimum bend radius, destroyed the inner wire, lost his job, and doomed himself to an eternity of unemployment.
What Hercules experienced was a hose that (to him) had a high flexibility, or low force to bend. Many hoses, such as stainless-steel braided Teflon, can physically be bent past the minimum bend radius with ease, thus damaging or kinking the inner core of the hose. Hose bend radius can be exceeded if the incorrect length is established for the application, or during mishandling during packaging, shipping, or installation. Because of this, it’s always important to examine your hose assembly for signs of over bending prior to installation and system startup. Mid-state has bend radius data on file for each of our hoses and are always happy to share this information upon request.
Now that we've gotten that out of the way, let's go over what bend radius is; the smallest looped diameter a hose can achieve without damaging the inner tube. Hoses produced to an SAE (Society of Automotive Engineers) specification are given a minimum bend radius, and some-manufacturers produce hoses with improved capabilities. For instance, our 100R4 suction hose is available with half bend radius, which allows it to bend twice as far as standard R4!
There are two methods to measure bend radius; inside-radius and centerline radius. Inside radius measures the distance between a hose’s inside edge when bent 90 degrees. Centerline radius is the distance from the theoretical zero-point to the exact centerline of a bent hose.
For the math lovers out there, minimum bend radius is calculated as L=A/360° x 2 TTr, where:
This formula allows one to determine the minimum required length of hose for any situation.
While failure is the number one concern, there are also auxiliary issues which may affect your hose assembly. Exceeding bend radius may restrict the flow of media passing through an assembly, and cause excessive heat-buildup due to the added friction. This may also reduce the overall pressure rating of your assembly, as the inner braided wire has been stretched thin enough to create gaps between the reinforcement strands. These factors, when combined with external elements such as extreme temperatures, UV exposure, or mishandling can contribute to untimely hose failure, ultimately creating the need for more frequent hose replacements, undue downtime and maintenance, system performance issues, and safety hazards.
Bend Radius should first be considered during the design phase, where you plan out the length of your assembly for the best fitting application.
Over bending can occur outside of routing. Treat hoses carefully in your facility. If you store assemblies, never wrap them too tightly to fit on a shelf or in a container. This could lead to kinking.
Always inspect your hose assemblies prior to installation for signs of damage. Kinking or over bending can occur during shipping and receiving. Ensure everyone who handles your hoses knows not to over bend.
If you’re not already privy, rubber hydraulic hoses are constructed of three basic components: the inner tube or core, reinforcement layers, and an outer cover. Inner tubes are typically constructed from rubber or synthetic compounds, but vary depending on the desired media. Reinforcement layers are mostly constructed from fiber braids, steel wires, or helical wires. Wire braids vary widely as well, ranging from 1-6 wires. Outer covers are composed of similar compounds to the inner tube, but often come with extra material designed for extra abrasion, temperature, or UV resistance. Thermoplastic and Teflon hoses are constructed in a similar fashion, but use non-rubber compounds for the inner cores and outer covers. Because these hoses are typically designed to handle more volatile media, their inner cores are typically stiffer and therefore kink much easier than rubber hose.
We’ll save the hose construction lecture for another article, but it’s important to understand the basic composition of hose in order to understand how much bend radius variation can occur between hoses. Each component of a hose is carefully designed in order to achieve a specific result, such as a higher-pressure rating or abrasion resistance. These added features affect the physical makeup of the hose and directly affect the bend radius. Because of this we do not recommend substituting hose brands or specifications without first considering bend radius, as a failure to do so may lead to unintended consequences.
In closing, we hope we’ve scared you out of the hose business and into something more respectable like accounting or the culinary arts. Seriously though, if you’re still with us we’re glad you came along for the ride. The often overlooked and convoluted aspects of hose selection and assembly design are usually ignored for a reason—it’s tough to keep track of all these details. It’s not all doom and gloom here though. Although bend radius is an important factor to consider, failure to adhere to a .5-degree tolerance doesn’t typically result in nuclear fallout. That said, there are many times when assembly length, end-connections, and routing can be improved upon in order to achieve longer hose life, better system performance, and the most important thing of all—save money!
If you’d like to learn more about how we can help audit your equipment for bend radius and other concerns, please reach out to us today. Our team of trained hose experts can analyze your equipment, and offer design, routing, and installation advice. Thanks for reading!