Copyright Goodheart-Willcox Co., Inc. Chapter 8 Fluid Storage and Distribution 187 accommodate attachment of system components to the conductors. In actual use, the number of such units must be minimized. Each additional fi tting placed in a system increases original cost and adds a point that may contribute to fl uid fl ow resistance and turbulence. Technicians who maintain fl uid power systems often feel that planning for maintenance and service is not considered during new system design and con- struction. Components may be assembled in such a way as to make service diffi cult. However, once major maintenance is required, design variations can often be made that will allow a system to be more easily repaired during future service. An example of this is retrofi tting components with fl are fi ttings in place of the original threaded pipe connections. 8.2.2 Types of Conductors A fl uid power system can incorporate a number of differ- ent conductors to transmit fl uid. The most common gen- eral classifi cations are pipe, tubing, and hose. A number of design variations, connectors, and fi ttings are available under each of these classifi cations. Also, some manufac- turers classify manifolds as conductors, although these are often considered separate components. The conductor used depends on a number of factors, ranging from sys- tem operating pressure to initial cost. Pipe Pipe is a high-tensile-strength, rigid fl uid conductor normally made from mild steel. It is normally installed by cutting and fi tting various lengths into the desired confi guration using threads cut directly on the pipe and threaded fi ttings. It is not intended to be bent. recommended velocity rates. Excessive velocity pro- duces fl uid turbulence, which increases fl ow resis- tance. See Figure 8-8. Smooth interior surfaces and gradual bends in conductors reduce the resistance to fl uid fl ow in a system. This helps promote laminar fl ow, or straight-line fl ow. The selection of a fl uid with the proper viscosity also helps ensure fl ow resistance is not too great in a system. Resistance to fl ow in lines and fi ttings results in energy loses in a system. The energy being input into a system can be calculated using the fl uid pressure and fl ow at the pump. As the fl uid is forced through the sys- tem, the fl ow rate remains the same, but the pressure drops as resistance is encountered. This pressure drop is the result of the resistance to fl uid fl ow caused by: • Each square inch of conductor surface. • Each bend or fi tting encountered. • Each orifi ce passed through. • Level of turbulence in the fl uid stream. • Viscosity of the fl uid. • Resistance of the external load. The pressure that is lost in the system due to all of these factors, except the external load, indicates the energy that has been lost in the system. This lost energy directly lowers the work output of the system. It also produces heat, which, in excessive amounts, can cause many system operating problems. Installation and maintenance To be effective, conductors must not only carry the fl uid from component to component, but must be con- structed in such a way as to allow economical instal- lation and maintenance. Connectors and fi ttings must Restriction to Flow Basic Flow Characteristic Contributing Factors Minimal Laminar flow • Adequate conductor diameter • Recommended flow velocity • Smooth conductor surfaces Excessive Turbulent flow • Small conductor diameter • Excessive fluid velocity • Inappropriate conductor fittings Goodheart-Willcox Publisher Figure 8-8. The inside diameter of a conductor must be large enough to move the fluid at a velocity no greater than the maximum recommended for the line. If this velocity is exceeded, fluid turbulence and power loss can result.