COMPOUND PATCH.- When repairing battle damage to piping systems, you will often work on a compound rupture, as shown in view A of figure 7-29. Compound ruptures may take a variety of shapes. Therefore, it is more difficult to select a single example to fit all repairs. In most compound ruptures, it should be possible to simplify the rupture by removing butterfly edges. You may also cut away the damaged section to form either a severed pipe or a simple pipe repair. Sometimes you cannot remove the butterfly edges or other projections by pounding them in or by cutting or burning them off. In that case, you can apply a simple pipe patch with the following modifications:

1. Tie the chalk line firmly between the jagged edges (view B of fig. 7-29), crisscrossing as much as possible. This chalk line acts as a support for the woven roving cloth and keeps it from falling into the void. No void cover is used in this example. It would be impractical to cut a void cover to suit the jagged edges.

2. Fold a small piece of impregnated woven roving cloth (view C of fig. 7-29); lay it in the void where it helps to build up the mass and acts as an insulator.

3. Apply the precut woven cloth (view D of fig. 7-29) over the small folded piece of woven cloth. Tie it firmly in place as outlined previously for the simple pipe patch.

FLANGE PATCH.- The flange patch is applied to a damaged flange (view A of fig. 7-30). The application is similar to that used for a single patch with the following modifications:

1. Cut the void cover into an H shape (view B of fig. 7-30), impregnate it with the resin-hardener mixture, insert it into the void, and tie it securely in place.

2. Cut your pieces of woven roving cloth, each of them long enough to make one complete turn around the pipe and overlap 1 inch. Cut these four pieces in an H shape, but do not cut away the center pieces. Instead, fold them up over the edges of the flange.

3. Impregnate the separate plies of woven roving cloth and place them over the rupture (view c of fig. 7-30).

4. Apply the PVC film and tie it down firmly, starting at one end working up to the flange. Make several windings of the chalk line through the gap in the flange in a figure X to have the woven roving cloth conform to the center of the rupture and the flange edges. Continue on to the opposite end of the patch and tie securely in place.

Repair Kit Review

An ideal plastic patch is one which can be applied and cured in the shortest time possible and will maintain the desired tightness. The primary factor controlling the kick-over time is the

Figure 7-30.-Flange rupture patch.

temperature of the resin and hardener before mixing. For the patch to cure in the shortest time possible, you must contain the heat generated in the patch. You do this by creating a mass about the break in the pipe or bulkhead rupture by using an impregnated woven roving cloth. You can see, therefore, that the correct amount of mass is necessary to have an effective patch. It is also important that the patch cools readily; you cannot restore pressure to the system until the patch cools to about 150F. The net result is that you build up a mass about the rupture that will give you a patch with the most desirable characteristics in the shortest possible time. The plastic pipe patch can withstand 300 psi at 200F.