Copyright Goodheart-Willcox Co., Inc. 328 Section 3 Plumbing System Design and Installation 21.4 Installing DWV Plastic Pipe and Fittings DWV plastic piping is generally measured by either the face-to-face or the shoulder-to-shoulder method. The fitting allowances (engagement) for DWV fittings are given in Figure 21-24. These allowances are the same for either ABS or PVC materials. For example, if the face-to-face measurement for a 2″ PVC pipe is 4′-6″ and the pipe must engage a fitting at both ends, then the pipe must be cut 4′-7 1/2″ long. This is an allow- ance of 3/4″ for each fitting, or a total of 1 1/2″. See Figure 21-25. The laying lengths for common types of ABS and PVC fittings are given in Figure 21-26. 21.4.1 Cutting Plastic Pipe PVC or ABS pipe is usually cut with a pipe cutter designed for plastic, Figure 21-27. Plastic pipe can also be cut with a fine-tooth saw, using a miter box to ensure that the cut will be square, Figure 21-28. All burrs on the cut end of the pipe should be removed with a reamer or abrasive paper. 21.4.2 Joining Plastic Pipe and Fittings Before solvent-cementing any type of plastic pipe, thoroughly clean the end of the pipe and the inside of the fitting. Mud or dirt should be wiped away before applying the solvent cleaner specifically prepared for the type of pipe and fittings being joined. The solvent cleaner both cleans the pipe and removes the surface gloss for better bonding. Choose the appropriate solvent cement for the type of plastic, Figure 21-29. Using the swab that is attached to the solvent cement cap, apply a light coat of the ce- ment to the fitting socket. Do not use the same swab to apply cleaning solvent and solvent cement. Next, apply a heavy coat of cement to the pipe end, Figure 21-30. Immediately insert the pipe all the way into the fitting socket while giving it a one-quarter turn to align with the mark indicating the finished position of the fitting, Figure 21-31. This rotation ensures that the solvent cement is evenly distributed in the joint. A small bead of solvent cement should be visible around the entire fitting. This indicates that the proper amount of cement A B Mark here To lavatories Foundation wall End of pipe to tub P-trap Goodheart-Willcox Publisher Figure 21-23. The length of the pipe connecting the double sanitary wye to the 45° ell of the bathtub can be determined by transferring dimension A to location B. Plastic Pipe Depth of Engagement Pipe size (in inches) Engagement (in inches) 1 1/4 1 1/2 2 1 1/16 1 1/16 3/4 3 4 6 1 1/2 1 3/4 3 Goodheart-Willcox Publisher Figure 21-24. Fitting allowances for various sizes of plastic pipe. 2″ Elbow Face 4uni2032-7½° 4′-6° ¾° ¾° Engagement 4uni2032-6° + 1½° = 4′-7½° Goodheart-Willcox Publisher Figure 21-25. When computing pipe length, be sure to include allowance for the depth of socket on each fitting.