Copyright Goodheart-Willcox Co., Inc. 192 Fluid Power A wide variety of pipe fi ttings are available to assist in constructing the conductors needed to carry the hydraulic fl uid to system components. These include tees, elbows, couplings, unions, nipples, and several other shapes, Figure 8-18. These fi ttings should be made from steel or other material that will ensure a strength comparable to the schedule of the connecting pipe. All connections should be installed to permit easy removal and reassembly by common hand tools. Union fi ttings allow easier connection of complex system lines. They provide a means of connecting lines using fl anges that provide a positive seal. However, every attempt should be made to design pipe runs between components with a minimum of unions. It is critical to plan the system so that pipe, fi ttings, and system valves can be removed without dismantling large sections of the system or bending or otherwise damaging system parts. Tubing A wide variety of fi ttings are available for making connections to tubing. Manufacturers produce many different styles that are designed to provide the best means of attaching tubing to system components, Figure 8-19. Each must provide a proper fi t and seal between the component and fi tting and also between the tube and fi tting. Typically, the seal between the fi tting and the sys- tem component is provided by either a tapered pipe thread or a straight thread with a separate seal. The separate seal may be an O-ring or a compression washer. The seal between the fi tting and the tube is pro- vided by either a fl ared or compression connection. Flared fi ttings actually require physically fl aring the end of the tube. A positive seal is provided by using a jamb nut and sleeve to force the fl ared tube end against a cone portion of the connection. In the United States, fl ared tube fi ttings are standardized at 37° and 45° angles. See Figure 8-20. Hydraulic systems typically use the 37° design. A number of different designs can be found in compression fi ttings for tubing. Several manufacturers have patented designs. Typically, these include a fi tting body, compression element such as an O-ring, ferrule, or proprietary compression sleeve, and compression nut, Figure 8-21. The end of the tube to be attached must be square, concentric, and free from burrs to ensure proper positioning and sealing. The tube end is slipped into the fi tting until it rests against an internal shoulder that provides proper positioning. Tightening the compression nut squeezes the parts to secure the tube and provide a fl uid-tight seal. The tube may be attached to the fi tting by swag- ing, brazing, or hard soldering. Swaging joins the tube Locking groove Disconnected (Check Valves Closed) Check valves Locking balls Spring-loaded, sliding collar Connected (Check Valves Open) Goodheart-Willcox Publisher Figure 8-16. Easily operated locking devices and effective check valves allow quick-disconnect couplings to be quickly operated without spilling fluid. B A Spiral clearance may be present, even when connection is tightened First contact when standard pipe threads are tightened First contact when Dryseal threads are tightened Full contact when threads are properly tightened Goodheart-Willcox Publisher Figure 8-17. Dryseal standard pipe threads should be used when constructing hydraulic system conductors from pipe. A—Standard pipe threads. B—Dryseal pipe threads.