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Whether you are replacing an existing hose, or building a new system, you’ll need to select a hose of the correct pressure rating, diameter, and length and with the best material properties for your application. There are a few factors to consider carefully.
Firstly, you should consider the conditions that a hose will operate under. The outer layer or cover of a hose can come in a variety of synthetic rubber materials. Some compositions can help with applications where abrasion may occur but may not bend as readily.
The most common materials are fluoropolymers and silicone, elastomers, metal, and thermoplastics. Composite or laminated materials are also common.
Rubber and elastomeric hydraulic hose are a strong choice when you need flexibility. A Fluoropolymer hose has a durable flex life, it also has excellent corrosion and chemical resistance and it can handle high temperatures.
Thermoplastic hydraulic hose has a tight minimum bend radius. It also features superior resistance to kinks. Thermoplastic hoses are generally much lighter than rubber hoses. The inner tube of copolyester or nylon is typically braided or spiral wrapped with a synthetic reinforcement fiber instead of steel. Synthetic fiber is also needed for electrically non-conductive (orange cover), aerial lift hoses. In many cases the outer cover of thermoplastic hoses will be polyurethane and provide a longer shelf life than rubber, better flexibility at low temperatures such as –60°C (–75°F), and higher resistance to UV and chemicals.
Metal hoses handle high temperatures and high flow materials well. They can also handle high pressures, as well as being either flexible or stiff.
Neoprene is one popular synthetic cover material that remains flexible across a wide range of temperatures, yet handles abrasion well. Most rubber hoses perform reasonably well from –40°C (–40°F) to 100°C (212°F).
Flexible hoses are easy to install and route compared to rigid tubing. The flexibility reduces noise and vibrations. It also dampens pressure surges and allows for movement between the parts.
Weight and Space
Another consideration when selecting a hose would be whether the weight and space are a concern, as is often the case with mobile machine. In this instance you would want to look for hoses with a thin-wall inner tube. Advances in synthetic rubber compounds allow for higher wall strength, allowing for a final product with a smaller outside diameter. Some manufacturers have moved to a reinforcement wire with an oval cross-section, as opposed to round, offering additional outside diameter (O.D.) and hose weight savings. These smaller O.D. hoses, referred to as compact models in many catalogues, also offer much tighter bend radiuses.
Inside diameter and Length
It’s very important to use a hose of the correct inside diameter. If the diameter is too small for a given rate of flow, the linear velocity will be too high and excessive velocity will translate into friction and turbulence, which when combined will surely result in noticeably higher system pressure and heat.
Correct hose length needs to allow for bending and flexing as a machine moves and articulates, and to make sure that no undue stress is caused at the crimped fittings. A hose that connects in a perfectly straight path from one component to another may shrink in length up to 4% at maximum pressure, so an allowance of extra length should be considered when making up the hose assembly. However, an excessively long hose adds restriction to flow, increasing system pressure and reducing system efficiency. A long hose length also requires a larger inner diameter to avoid excessive restriction and friction.
A hose must be chosen with a maximum working pressure (WP) rating that is at or preferably above the normal maximum hydraulic system pressure. Momentary pressure surges for a hydraulic system are not to exceed this pressure rating. Hose fittings that are rated below the working pressure of the selected hose cause the entire hose assembly to be aligned to the lower rating of the fittings.
Burst pressure is a built-in safety factor for a hydraulic hose. A hose manufacturer verifies the burst pressure in a destructive test. The SAE standard J517 for the common series of 100R hydraulic hoses categorises leakage and also hose separation from hose fitting. The hose does not have to violently break apart completely to have suffered a burst failure. The burst pressure rating of a hydraulic hose if often 4x the working pressure rating or greater.
When it comes to hydraulic design, hoses are not minor parts. Using economics as the only/primary hose selection criteria can easily leave human risks at a very high level. A hose burst failure is always a catastrophic incident. In the best case scenario, a hose failure might cause production downtime or environmental contamination concerns. In a worse scenario, persons could be seriously injured or even killed.
Hydraulic hoses comes in a myriad of design types and materials, and choosing the correct type for your application involves understanding several factors. You now have the rudimentary understanding needed to select the proper hydraulic hose for your needs. Remember that choosing the correct type and grade hose will extend its working life.
If you have more questions about hydraulic hoses, please contact us.
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