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60 AUGUST 2015 Hose vs. Tube: What's the Best Call for Hydraulic Equipment? What do cranes, bladder-type accumu- lators, and hydraulic hoses have in common? Well, they typically have only one mode of failure - and it’s catastrophic. One minute they’re working as they should, and the next thing you know, they’re not. Oh, sure, hoses can leak from around their ferrules and show obvious signs of abrasion, both of which are early warning signs a change-out would be prudent. But even under these conditions, estimating their remaining service life is virtually impossible. Transmitting power from one location to another is a key element in a system’s design and performance. This transmitting of power is known as fluid conducting. Fluid conductors describe different types of conducting lines that carry hydraulic fluid between components. The three principal types of plumbing materials used in hydraulic systems are steel pipe, steel tubing, and flexible hose. A safety factor of 4 to 1 is recom- mended on the pressure rating of the plumbing material. To deter- mine the working pressure of the conductor, the rated burst pressure is divided by a safety factor of four. The Trouble with Hose Hydraulic hoses are used in applications where lines must flex or bend. When using hoses, system pressure, pressure pulses, velocity, fluid compatibility, and environmental conditions must all be considered. The Society of Automotive Engineers under SAE J5-17 has standardized hose construction. This is known as the R series (for example, 100R2 or 100R4). This designation describes the cover, construction, pressure rating, and application. Hoses are usually pressure rated with a safety factor of 4 to 1. Different types and amounts of reinforcement give the hose specific pressure ratings. The reinforcement may be a natural or synthetic fiber or metal wire. The reinforcement may be braided or spiral bound. Required hose size depends on the volume and velocity of the fluid flow. Unlike pipe and tubing, hose sizes are designated by ID or inside diameter. Sizes are designated in 16ths of an inch by using a dash and a number equivalent to the numerator of the fraction. Example: dash 8 (-8) or 8/16-inch or half-inch ID Hoses can last a long time, but all rub- ber slowly deteriorates with contact from various substances, such as solvents, water, sunlight, and heat. Hoses are not as permanent as metal conductors and should be replaced every few years. We will be continuing this discussion in our next few articles. Eric may be contacted via e-mail at michele@ worldwidedrillingresource.com Hydraulic Training by J. Eric Freimuth Hydraulic Training Associates WorldWide Drilling Resource ®