When working with plumbing systems—whether for Pressure, Stormwater, or Drainage, Waste & Vent (DWV)—it's important to understand how pipe sizing works and why it matters. All pipes and fittings sold in Australia are manufactured to meet Australian Standards, ensuring consistency, safety, and compatibility within each system type.
Nominal Pipe Sizes Explained
Pipe and fitting sizes are referred to as nominal, meaning the size designation (e.g., 100mm or 150mm) does not directly reflect the actual internal or external diameter of the pipe. This standardization helps prevent the mixing of incompatible components across different systems.
For example:
- A 150mm DWV fitting will not fit a 150mm Pressure or Stormwater pipe.
- It is designed only for use with 150mm DWV pipe.
This deliberate incompatibility ensures that each pipe type is used correctly and safely for its intended application.
Why Compatibility Matters
Each pipe system—Pressure, Stormwater, and DWV—has unique performance requirements. Mixing fittings from different systems can lead to leaks, failures, or non-compliance with building codes. That’s why manufacturers design fittings to be system-specific.
As long as fittings and pipes are matched within the same system and nominal size (e.g., 65mm DWV fitting with 65mm DWV pipe), they will be compatible—even if there are slight variations between manufacturers.
Technical Guides for Reference
To help you choose the right products, here are technical guides from IPEX that outline sizing and compatibility:
- Stormwater Pipe & Fittings
Stormwater-Pipe-Fittings-Technical-Guide.pdf - DWV Pipe & Fittings
DWV-Pipe-Fittings-Technical-Guide.pdf - PVC Pressure Pipe & Fittings
PVC-U-Pressure-Pipes-and-Fittings-Technical-Guide.pdf
Key Takeaways
- Pipe sizes are nominal, not exact measurements.
- Compatibility is system-specific—never mix DWV, Pressure, or Stormwater fittings.
- All products sold in Australia comply with Australian Standards.
- Always refer to technical guides when selecting pipe and fittings.