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I DA U N I V E R S A L J u l y -Au g u s t 2 0 1 6 38 right combination of fl uid compatibility and the chemistry of the hose layers, according to Derek Garceau, engineering manager for Parker's Hose Products Division. "Variables ranging from temperature, working pressure, and fl uid compatibility, along with restrictions inherent in the customer's application, make it challenging to deter- mine the right hose for an application," he says. "It's a balancing act between the compatibility of the inner tube with the fl uid being used, and the conditions of the specifi c application, such as repeated fl exing or high operating temperatures," Garceau says. "Both can aff ect each other's performance. For example, having more material in the polymer to resist the fl uid o en decreases its ability to withstand extreme temperatures." Cold temperatures can also aff ect the fl uid being transferred through the hose. For example, cold tempera- tures may thicken the fl uid, decreasing its fl ow rate. And adding more insulation or heated sleeves to the hose isn't always viable. In many of today's vehicles, hoses are routed to save space and cost. is does not leave a lot of room to install an insulated hose or additional sleeving. "We can't make the hose two inches in diameter if the client needs it to be half-an- inch in diameter," Garceau says. "We usually recommend end-users complete a warming procedure prior to use, in which they let oil circulate through the hose until it's up to a working temperature." Other Challenges Not all challenging applications involve extreme temperatures. In one case, for example, Boeing wanted to simulate fl ight conditions in its 787 Dreamliner while it was still on the assembly line to check the hydraulic pressures. e Dreamliner uses higher hydraulic pressures than most commercial aircra . For the test, Boeing needed a 6,000 psi hose to validate the aircra 's functions. At the time, no hose on the market, compatible with aviation fl uid, carried a 6,000- psi rating. In fewer than four months, Parker designed, tested, and manufactured its F42 hose made out of an ethylene propylene diene monomer (EPDM)-based rubber. Rated at 6,000 psi and compatible with aviation fl uid, the hose also meets other Boeing requirements for bend radius, fl exibility, and life. EPDM is a base polymer used to make rubber hoses. It is a high-density synthetic rubber, compatible with fi reproof hydraulic fl uids, ketones, hot and cold water, and various alkalis. EPDM hoses resist heat, ozone, and weather, and maintain excel- lent fl exibility at high and low temperatures. Parker's EPDM hose provides reliable, constant working pressures of up to 6,000 psi in temperatures from -40° to 176°F (-40°C to 80°C). A second commonly used chemical is a nitrile-based polymer, which is a synthetic rubber copolymer of acrylo- nitrile (ACN) and butadiene. Nitriles provide good compat- ibility with oils and standard hydraulic fl uids. "When designing nitrile rubber hoses for customers, engineers pay close atten- tion to the ACN content in the mixture," Groves notes. " e higher the ACN content, the better the polymer resists certain nonpolar solvents Hoses are designed in layers that get stacked on top of each other, starting with an inner tube layer that resists the transmitted fl uid, a reinforcement layer for pressure carrying capability, and a cover (perhaps an elastomer) that helps it resist abrasions. Hoses Continued from page 37