By Josh Cosford, Contributing Editor
Hydraulic hoses are stressed in two directions — bending and rotating. Hose is designed with reinforced steel spirals or mesh weave, making it perfect for bending, even while internal force exerts stress upon the hose. Torque, on the other hand, makes friends with no hydraulic hose. If you’ve ever tried to twist a hydraulic hose, you’ll recall how vehemently the hose resists torque.
Excessive torque applied to a hydraulic hose creates structural damage and distortion of the reinforcement layers, in addition to the potential for delamination of the inner tube or outer carcass. When torque is excessive, you may even rip the hose from the crimp fitting entirely, causing catastrophic failure.
Image courtesy of Super Swivels
In the best-case scenario, repeated applications of torque will fatigue the hose assembly prematurely, leading to eventual blowouts or leaks. Some hydraulic hose will inherently coil and form a helical shape as it resists torque, creating tension in addition to the twisting force.
Torque is the result of hose moving between one fixed location and one pivoting joint while also rotating about its axis. Torque may also occur where one end of a hose is fixed and another is mounted to a portable tool or device, such as a handheld, high-pressure hydraulic torque wrench. Although hydraulic tools won’t experience massive torque loads through operator manipulation, the rotational stiffness of the hose makes it difficult to maneuver without bunching up or tangling.
To avoid torque-related damage, I recommend a swivel joint. These joints allow for rotational movement at a fixed connection joint and the hose connected to it. Any torque applied is mitigated while the hose simply rotates, preventing any of the above potential damage. The swivel joint uses internal, high-pressure seals and wear strips to contain pressure while allowing slip, so long as rotational speed is reasonable (these are swivel joints, not high-speed rotating unions).
Swivel joints are available in many sizes and flow ranges, as well as many conventional port styles. Inline construction is standard, although 90° style and dual plane construction are also available from many manufacturers. A 90° swivel is self-explanatory, as these joints are perfect for plumbing straight from a port or fixed connection that must allow for radial movement of the hose or pipe to which it’s attached.
The dual plane swivel offers easy movement with simultaneous pivoting and rotating, making it great for hose assemblies that hang high on the wall or ceiling, or such as a boom crane with external plumbing. Going a step further, the Z-swivel can move in three planes, allowing movement in all directions. When it comes to using handheld hydraulic machinery, like nut splitters or torque wrenches, the Z-swivel offers maximum range of motion with no binding.
The available range of sizes and flow rates will suit the majority of hydraulic applications, with some manufacturers offering their swivels up to 2-1/2 in. ports. Flow rating directly correlates with size, of course, but depending on the configuration, you can expect up to 200 gpm or more. Just as with many other hydraulic components, pressure ratings are reduced at higher flow rates.
Some swivel joint manufacturers offer many of their products with differing thread forms and genders. For example, purchasing a male ORB with male JIC avoids having to purchase bulky adapters, reducing cost and installation complexity. A final bit of ingenuity integrates a bulkhead adapter’s male straight thread, such as JIC and ORF, providing an all-in-one solution with three fittings packaged into one.
Although elementary in concept, swivel joints have come a long way from the simple, inline male to female options of the past. If you have any rotational or free-movement requirements in your application, be sure to research your myriad options available for swivel joints; you could improve the effectiveness of your plumbing while also reducing investment cost and installation time.
Filed Under: Components Oil Coolers, Engineering Basics, Featured, Fittings, Couplings & Adapters, Hose Assembly Tips
