Once flexible hose assemblies are installed,there are no servicing or maintenance require-ments other than periodic inspections. Theseinspections are conducted according to mainte-nance instruction manuals (MIMs), maintenancerequirement cards (MRCs), and depot-levelspecifications.TYPES OF FITTINGSAND CONNECTORSSome type of connector or fitting must beprovided to attach the lines to the components ofthe system and to connect sections of line toeach other. There are many different types ofconnectors and fittings provided for this purpose.The type of connector or fitting required for aspecific system depends on several factors. Onedetermining factor, of course, is the type of fluidline (pipe, tubing, or flexible hose) used inthe system. Other determining factors are thetype of fluid medium and the maximum operatingpressure of the system. Some of the most commontypes of fittings and connectors are described inthe following paragraphs.THREADED CONNECTORSThere are several different types of threadedconnectors. In the type discussed in this section,both the connector and the end of the fluid line(pipe) are threaded. These connectors are used insome low-pressure fluid power systems and areusually made of steel, copper, or brass, and areavailable in a variety of designs.Threaded connectors are made with standardpipe threads cut on the inside surface. The endof the pipe is threaded with outside threads.Standard pipe threads are tapered slightly toensure tight connections. The amount of taper isapproximately 3/4 inch in diameter per foot ofthread.Metal is removed when a pipe is threaded,thinning the pipe and exposing new and roughsurfaces. Corrosion agents work more quickly atsuch points than elsewhere. If pipes are assembledwith no protective compound on the threads,corrosion sets in at once and the two sectionsstick together so that the threads seize whendisassembly is attempted. The result is damagedthreads and pipes.To prevent seizing, a suitable pipe threadcompound is sometimes applied to the threads.The two end threads must be kept free of5-12compound so that it will not contaminate thefluid. Pipe compound, when improperly applied,may get inside the lines and components anddamage pumps and control equipment.Another material used on pipe threads issealant tape. This tape, which is made of PTFE,provides an effective means of sealing pipeconnections and eliminates the necessity oftorquing connections to excessively high valuesin order to prevent pressure leaks. It also providesfor ease of maintenance whenever it is necessaryto disconnect pipe joints. The tape is applied overthe male threads, leaving the first thread exposed.After the tape is pressed firmly against thethreads, the joint is connected.FLANGE CONNECTORSBolted flange connectors (fig. 5-14) aresuitable for most pressures now in use. Theflanges are attached to the piping by welding,brazing, tapered threads (for some low-pressuresystems), or rolling and bending into recesses.Those illustrated are the most common types offlange joints used. The same types of standardfitting shapes (tee, cross, elbow, and so forth) aremanufactured for flange joints. Suitable gasketmaterial must be used between the flanges.WELDED CONNECTORSThe subassemblies of some fluid powersystems are connected by welded joints, especiallyin high-pressure systems which use pipe for fluidlines. The welding is done according to standardFigure 5-14.—Four types of bolted flange connectors.
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