FITTINGS. - The fittings used on either wrought-iron or steel pipe are generally made of malleable iron or cast iron. There are two types of iron pipe fittings: the pressure type and the recessed type. To compare these two types of fittings, study figure 3-57.
The pressure type of fitting is the standard fitting used on water pipe. The recessed type of fitting, also known as a cast-iron drainage or Durham fitting, is generally required on all drainage lines. The recessed type is most suitable for a smooth joint; it reduces the probability of grease or foreign material remaining in the joint and causing a stoppage in the line. Recessed fittings are designed so horizontal lines entering them have a slope of l/4 inch per foot.
Types of iron pipe fittings include elbows, crosses, tees, and unions The four types of elbows are 90-degree, 45-degree, street, and reducing elbows. The 90-degree elbow changes the direction of an iron pipe 90 degrees, and a 45.degree elbow changes the direction by 45 degrees.
STREET elbows change the direction of an iron pipeline in a closed space where it is impractical to use an elbow and nipple. Both 45- and 90-degree street elbows are available. Street elbows have one female and one male thread, rather than two female threads.
The REDUCING elbow is similar to the regular 90-degree elbow, except that one opening is smaller than the other. For instance, a 3/4-inch pipe can be screwed into one opening of this fitting and a l/2-inch pipe into the other opening.
Figure 3-57. - Pressure and recessed (Durham) fittings.
An iron pipe CROSS is made of malleable iron in straight and reducing patterns and has female threads at all four branch points.
A common type of iron pipe tee is the STRAIGHT tee which has a portion that is straight through and a 90-degree takeoff on one side. All three openings of the straight tee are of the same size. Another common type is the REDUCING tee, similar to the straight tee just described, except that one of the threaded openings is of a different size than the others.
There are two types of iron pipe unions. They are the ground joint union and the flange union. The GROUND JOINT union consists of three pieces, and the FLANGE union is made in two parts. Both types are used for joining two pipes together and are designed so they can be disconnected easily.
Other types of iron pipe fittings include couplings, nipples, pipe plugs, pipe caps, and pipe bushings. Each fitting is discussed briefly.
Three common types of couplings are straight coupling, reducer, and eccentric reducer (fig. 3-58). The STRAIGHT COUPLING is for joining two lengths of pipe in a straight run that do not require additional fittings. A REDUCER joins two pipes of different sizes. The ECCENTRIC REDUCER has two female threads of different sizes with different centers so, when joined, the two pieces of pipe are not in line with each other. It is installed to provide optimum drainage of the line.
A NIPPLE is a short length of pipe (12 inches or less) with a male thread on each end. It is used as an extension for a fitting. In plumbing work, nipples are often used. Nipples are available in many precut sizes. Figure 3-58 shows several common types of nipples.
Pipe PLUGS are fittings with male (outside) threads. They are screwed into other fittings to close openings. Pipe plugs have various types of heads, such as square, slotted, and hexagon sockets (fig. 3-58).
A pipe CAP (fig. 3-58) is a fitting with female (inside) threads. It is used like a plug. It screws on the male thread of a piece of pipe.
A pipe BUSHING is a special fitting with a male thread on the outside and a female thread on the inside (fig. 3-58). Bushings reduce the size of openings of fittings and valves to a smaller diameter. 3-45Continue Reading