Figure 8-4.-Comparison of pressure and recessed (Durham)types of fittings.also be adapted to metal pipe fittings. The fittingsused on either steel pipe or wrought iron aregenerally made of malleable iron or castiron. There are two types of iron pipe fittingsused: the PRESSURE type and the RECESSEDtype (fig. 8-4).The pressure type of fitting is the standardfitting used on water pipe. The recessed type offitting, also known as a cast-iron drainage orDurham fitting, is generally required on alldrainage lines. The recessed type is most suitablefor a smooth joint; it reduces the probability ofgrease or foreign material remaining in the jointand causing a stoppage in the line. Recessedfittings are designed so that horizontal linesentering them will have a slope of one-fourth in.per foot.ELBOWS (OR ELLS) 90° AND 45°.— Thesefittings (fig. 8-5, close to middle of figure) are usedto change the direction of the pipe either 90 or45 degrees. REGULAR elbows have femalethreads at both outlets. STREET elbows changethe direction of a pipe in a close space where itwould be impossible or impractical to use anelbow and nipple. Both 45- and 90-degree streetelbows are available with one female and one malethreaded end. The REDUCING elbow is similarto the 90-degree elbow except that one openingis smaller than the other.TEES.— A tee is used for connecting pipes ofdifferent diameters or for changing the directionof pipe runs. A common type of pipe tee is theSTRAIGHT tee, which has a straight-throughportion and a 90-degree takeoff on one side. Allthree openings of the straight tee are of the samesize. Another common type is the REDUCINGtee, similar to the straight tee just described,except that one of the threaded openings is of adifferent size than the other.UNIONS.— There are two types of pipeunions. The GROUND JOINT UNION consistsof three pieces, and the FLANGE UNION ismade in two parts. Both types are used forjoining two pipes together and are designed so thatthey can be disconnected easily.COUPLINGS.— The three common types ofcouplings are straight coupling, reducer, andeccentric reducer. The STRAIGHT COUPLINGis for joining two lengths of pipe in a straight runthat does not require additional fittings. A runis that portion of a pipe or fitting continuing ina straight line in the direction of flow. AREDUCER is used to join two pipes of differentsizes. The ECCENTRIC REDUCER (also calleda BELL REDUCER) has two female (inside)threads of different sizes with centers so designedthat when they are joined, the two pieces of pipewill not be in line with each other, but they canbe installed so as to provide optimum drainageof the line.CAPS.— A pipe cap is a fitting with a female(inside) thread. It is used like a plug, except thatthe pipe cap screws on the male thread of a pipeor nipple.PLUGS.— Pipe plugs are fittings with male(outside) threads. They are screwed into otherfittings to close openings. Pipe plugs have varioustypes of heads, such as square, slotted, andhexagonal sockets.NIPPLES.— A nipple is a short length of pipe(12 in. or less) with a male thread on each end.It is used for extension from a fitting.At times, you may use the DIELECTRIC orINSULATING TYPE of fittings. These fittingsconnect underground tanks or hot-water tanks.They are also used when pipes of dissimilar metals8-4
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