Copyright Goodheart-Willcox Co., Inc. Chapter 8 Fluid Storage and Distribution 199 are appropriate. Tubing sections that are the incorrect length or do not contain the proper bend angles will cause stress on all parts involved. This occurs when they are sprung into position or forced into alignment when fi ttings are tightened. 8.5.3 Hose Hose allows the transmission of hydraulic fl uid between stationary and movable machine components. Although hoses are fl exible to provide this connection, they must be installed according to manufacturer specifi cations to obtain maximum service life. A wide variety of materials and manufacturing methods are used by hydraulic hose producers. This makes selection of a specifi c hose for an application more complicated. Basic factors to consider when selecting a hose for an application are: • Pressure and fl ow ratings. • Chemical resistance to the fl uid used in the system. • Resistance to external abrasion. • Flexibility. Once these factors have been established, specifi c installation factors must be considered. Changes in system pressure must be considered when working with hose. As the pressure increases, the length of the hose tends to decrease and its diam- eter tends to increase. Always provide some slack in a hose during assembly to allow for length change. See Figure 8-27. When the hose passes through openings in machine members, be sure adequate clearance is pro- vided for increases in hose diameter. Also, be careful to avoid any twists in hoses when the installation is com- plete. See Figure 8-28. Pressure tends to straighten the hose, which can actually loosen fi ttings. In addition, Pipe sections should fi t without being distorted or placed under tension. Both of these conditions will cause stress on the pipe and other components. This stress could result in material fatigue and lead to part failure. Careful planning must also be done to allow easy removal of components during system service. This may require the use of unions to provide an easy means of removing pipe, fi ttings, and components. 8.5.2 Tubing Tubing is more expensive than pipe. However, it is more easily installed, lighter in weight, produces less fl ow resistance, and generally provides a neater instal- lation. The number of fi ttings can be reduced in a tube installation by bending the tubing whenever possible. Manufacturer specifi cations indicate the minimum radius of bends for each type, diameter, and wall thick- ness of tube. Kinks, fl attened spots, and wrinkles can be avoided when fabricating tube sections by using the proper bending equipment. Both hand-operated and power benders are available for making up tube sections. Straight-line connections between components should be avoided in tube installations. These con- nections place excessive stress on the tube, tube fi t- tings, and system components. The use of strategically placed bends provides connections that will perform very well in most installations. Long lengths of tube should be supported by brackets or clamps to secure the conductor to the equipment. This is done to prevent fatigue caused by vibration or the weight of the tube and the hydraulic fl uid it contains. Care must also be taken when fabricating sec- tions of tubing to ensure the completed tube sections are the correct length and the angles of the bends Correct Incorrect Gates Corporation Figure 8-27. When installing hydraulic hose, always provide slack in lines. This counters the effect of the hose expanding in diameter and decreasing in length as system pressure increases.