rings in the two outer grooves of the coupling are compressed to seal the joint tightly. The T-shaped center ring forms a seal between the pipe ends to eliminate jogs and pockets and to provide for uninterrupted flow. In this type of joint, you have a tight and flexible connection.

A joint like the one shown in the figure can be assembled entirely by hand. After making sure the rings in the grooves of the coupling are in correct position, use the following two-step procedure, shown in figure 3-64, to make the connection.

1. Apply a thorough coating of lubricant to the male end of the pipe, all the way around (view A, fig. 3-64). If a special lubricant supplied by the manu- facturer is not available, prepare a jellylike soap solution instead.

2. Pull or push the pipe together, as shown in view B of figure 3-64, and the joint is complete.

Ductile Iron Pipe

Ductile iron is cast iron in which the carbon is reformed by magnesium inoculation. This results in exceptional strength characteristics without otherwise

Figure 3-64. - Steps in assembling a cement-asbestos pipe joint.

changing the basic nature of the cast iron. Because of this treatment, ductile iron has exceptional strength with good machinability, high impact, corrosion resistance, and great beam strength. For these reasons, ductile iron pipe is ideal for transportation of water.

When laying this pipe, you should ensure that both the bell and plain ends are clean. This is to prevent leaking joints. Sand, dirt, excess coating, ice, and other foreign material should be removed carefully from the plain end and the interior of the bell. This ensures proper seating of the gasket and correct entry of the plain end into the bell socket. The direction of the bells is not related to the direction of water flow within the pipe.

The mechanical joint for ductile iron pipe has four parts: a flange cast integrally with the bell of the pipe; a rubber gasket fitting a recess in the socket; a gland, or follower ring, to compress the gasket; and bolts and nuts for tightening the joint. The assembly of the joint is simple and requires only a wrench to tighten the nuts.

If the pipe must be cut, it may be cut with an abrasive wheel, a rotary wheel cutter, a guillotine pipe saw, a milling wheel saw, or an oxyacetylene torch. Of these cutting tools, the abrasive wheel saw is used most often for out-of-trench cuts; while the oxyacetylene torch method is used in trench cuts. Cut ends and rough edges should be ground smooth. For push-on type connections, the cut end should be beveled slightly.

Because of the high-impact strength of ductile iron, you only need to remove rocks and boulders 8 inches or greater in diameter from the material to be used as backfill.

Concrete Pipe

An extremely dry mix of cement, sand, gravel, and water with or without additives is used and cast in steel forms to manufacture concrete pipe. Concrete pipe can be reinforced with welded wire fabric or rebar. It is normally a flared bell-and- spigot-type pipe, similar to cast-iron soil pipe, but in larger sizes, 10 inches and above. The bell and spigot have a smooth configuration.

FITTINGS. - The fittings are the same as cast- iron and vitrified clay pipe, using a flared bell-and- spigot joint, or a smooth bell and spigot. This joint is called the "slip joint."

CUTTING. - A portable concrete saw is used to cut concrete pipe reinforced with steel. When cutting