Copyright Goodheart-Willcox Co., Inc. Chapter 8 Fluid Storage and Distribution 191 These additional fi ttings also facilitate disassembly and assembly during system service. Applications that require frequent or rapid con- necting and disconnecting of lines use quick-disconnect couplings. These fi ttings are commonly found on mobile equipment that uses a variety of interchangeable hydrau- lic implements. The couplings allow implements to be quickly changed with little or no fl uid loss, Figure 8-15. Quick-disconnect couplings contain an easily operated locking device and check valves. The lock- ing device can usually be operated without tools. The check valves prevent fl uid loss when the coupling parts are disconnected. See Figure 8-16. Pipe The sections of pipe used as fl uid conductors in hydrau- lic systems are typically assembled using threads. Thread sizes are standard, even though the outside diameter of the pipe varies slightly. A pipe thread con- nection includes external threads cut on the pipe ends and internal threads cut into the openings of system components and pipe fi ttings. The threads are tapered 3/4″ per foot to ensure a positive seal at the connection. A Dryseal pipe thread should be used, rather than standard pipe threads, when assembling pipe for use as a hydraulic system conductor. This thread design provides a tight seal that prevents the leakage encoun- tered when standard pipe threads are placed under high system pressure. Standard threads tend to leak because of a continuous internal spiral clearance that exists in the threads. See Figure 8-17. Spiral clearance is the result of space between the crests and roots of the threads when assembled. This clearance exists in a spiral along the entire length of the thread, even when the threaded parts are properly fi tted and tightened. a full range of operating situations. Although these specifi cations are available, standardizing groups typi- cally do not certify specifi c manufacturers or products. The standards are voluntary, but are very helpful when comparing products available from the many different hose manufacturers. Manifolds Manifolds are machined or fabricated machine elements used to distribute hydraulic system fl uid. A manifold may be as simple as a larger-diameter pipe that serves as a common oil supply to several valves or actuators in a sys- tem. However, manifolds usually serve more-complex, multiple-valve situations and involve machined passages in blocks or multilayer subplates. These units eliminate pipe, tube, or hose between components. This allows a lighter, more-compact system. 8.2.3 Conductor Fittings for System Assembly Constructing a hydraulic system requires a number of fi ttings to connect the conductors to the reservoir, pump, valves, actuators, and other component parts. The variety of fi ttings available from manufacturers for each of the various conductor types often makes selection confusing. However, selecting appropriate fi ttings is necessary to ensure reasonable initial con- struction cost, effi cient system operation, and minimal ongoing maintenance. Fittings serve as the means by which the ends of individual conductor sections are attached to other conductors or system components. Adapter fi ttings are often used between the conductor and the component to allow appropriate installation angles and clearances. B A Sporlan Division, Parker Hannifin Corporation Figure 8-14. Flexible hydraulic hose is made up of a minimum of three layers of materials. These include an inner layer for sealing, middle layer for strength, and outer layer for protection. A—Braided wire. B—Spiral-wound wire. Quick- disconnect couplings Goodheart-Willcox Publisher Figure 8-15. Quick-disconnect couplings allow hydraulic lines to be quickly connected or disconnected. This allows, for example, implements to be quickly transferred on mobile farm and construction equipment.