Charlotte Pipe 1-1/2 inch white PVC repair coupling with hub-by-hub ends

PVC Pipe Fittings: Schedule 40 vs. 80, Fitting Types, and How to Size Them

Most PVC fitting mistakes aren't visible until the line is pressurized or the joint is buried behind a wall - a mismatched schedule, the wrong joint type, or a size that's off by one nominal step. Here's how to get diameter, schedule, and joint type right before you glue anything.

Schedule 40 vs. Schedule 80: wall thickness, not just a label

Schedule refers to wall thickness and pressure rating, not diameter - a Schedule 40 and Schedule 80 fitting in the same nominal size have the same outside dimensions to fit the same pipe, but Schedule 80 has a thicker wall and a higher pressure rating. Schedule 40 covers the large majority of residential water supply, DWV (drain-waste-vent), and general low-pressure runs. Schedule 80 steps up for higher-pressure lines, industrial and chemical service, or anywhere the extra wall thickness and durability are worth the added cost. Don't mix schedules on the same run based on what's in stock - check the pressure rating the application actually calls for.

Slip (solvent weld) vs. threaded: pick based on whether the joint needs to come apart

Slip fittings are solvent-welded - primer and cement create a permanent, fused joint that's standard for most supply and drain runs. Threaded fittings (MPT/FPT) exist for connections that need to be serviceable, or where PVC transitions to metal pipe, a valve, or a fixture. Once a slip joint is welded it isn't coming apart without cutting it out, so use threaded or a union anywhere you'll need to service or replace that section later.

Common fitting types and what each one does

  • Coupling: joins two straight pipe ends in-line
  • Elbow (90°, 45°, or street): changes direction; a street elbow has one spigot end that fits directly into another fitting without an extra piece of pipe
  • Tee: splits a line into a branch
  • Wye: branches at an angle, common on drain lines where flow direction matters
  • Adapter: transitions between slip and threaded, or between PVC and another material
  • Cap and plug: terminate a line - a cap fits over the pipe end, a plug threads or slips into a fitting
  • Union: a removable threaded joint for sections that need to come apart for service
  • P-trap: the drain trap that holds a water seal against sewer gas at a fixture

Sizing: nominal size vs. actual outside diameter

PVC pipe is labeled by nominal size (1 in., 1-1/2 in., 2 in., etc.), but the actual outside diameter is larger than the nominal number - that's what determines which fitting size actually slips over or into it. Match the fitting to the pipe's real OD, not the nominal label, especially when you're combining pipe and fittings from different sources.

Solvent welding basics

Clean and deburr the cut end, apply primer (typically purple, to both the pipe and the fitting socket) to soften and prep the surface, then apply cement and join the pieces with a quarter-turn twist to spread it evenly. Hold the joint together for the few seconds it takes to set - a joint pulled apart before that will be weak even if it looks fine.

Buying to match your actual usage

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Quick buying checklist

  • Match schedule (wall thickness/pressure rating) to the application, not just the diameter
  • Use solvent-welded slip joints for permanent runs, threaded or union fittings anywhere the joint needs to be serviceable
  • Size fittings to the pipe's actual outside diameter, not just the nominal label
  • Use primer before cement on every solvent weld - don't skip it to save time
  • Don't mix schedules on the same run without checking the pressure rating the job needs
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