Polyvinyl Chloride, or PVC, pipe is used for both sewer and vent pipelines. For home use, it comes in diameters ranging from 1 1/2 to 4 inches -- lengths are generally 8 or 12 feet long. The pipe sections are tough and durable, and they join together using couplings, primer and cement. Use different types of PVC pipe for underground installation than you would for above-ground, in-house installation.
PVC pipe comes in different schedules (meaning wall thicknesses), the most common being Schedule 40, 80 and 120. Schedule 40, used for general household above-ground sewer and vent lines, has thinner walls, while Schedule 120 has the thickest walls of the three schedules. Where the outer diameter of each pipe is the same for each schedule, the inner diameter changes commensurate to the thickness of the pipe walls -- the inner diameter of Schedule 120 will be smaller than Schedule 80, and Schedule 80 will have a smaller inner diameter than Schedule 40.
Though all three schedules of PVC pipes are suitable for uses at temperatures up to 140 degrees, the pressure rating, or how much pressure can be applied to the pipe varies. Schedule 40 has a pressure rating of 120 to 810 psi (pounds per square inch), depending on its diameter size. Schedule 80 has a pressure rating of 210 to 1230 psi, and Schedule 120 has a pressure rating of 380 to 1,010 psi.
Schedule 120 PVC is generally used for industrial or high-pressure installations. Schedule 80 is used for applications where a higher pressure rating is required by code than the standard household Schedule 40 PVC.
When installing PVC pipes underground, the backfill on top of the pipe will vary in weight depending on how deep the pipe is installed in the ground. Schedule 80 PVC, due to it thicker walls, will stand up to more pressure from the backfill than Schedule 40 PVC. Local building code regulations differ regionally, so consult the local building code office for requirements when any PVC pipe is installed. The local office's code requirement, whether dictating Schedule 40 or 80, is always the last word.