A plumber is installing a water distribution system in a new home using PEX tubing. The local code allows the use of PEX-a, PEX-b, and PEX-c. Which of the following statements accurately describes a key characteristic or application difference between these types of PEX tubing?
- APEX-c is manufactured using the Engel process, resulting in the highest degree of cross-linking.
- BPEX-a is generally more rigid and has a higher burst pressure rating than PEX-b or PEX-c.
- CPEX-b is the most flexible and commonly used type for radiant heating applications.
- DPEX-a has the 'shape memory' characteristic, allowing it to be expanded for fittings and return to its original size.
Show answer & explanationAnswer & explanation
Correct answer: D. PEX-a has the 'shape memory' characteristic, allowing it to be expanded for fittings and return to its original size.
PEX-a is manufactured using the Engel method (peroxide cross-linking), which results in a higher degree of cross-linking and a unique 'shape memory' property. This allows PEX-a to be expanded using an expansion tool for fittings (e.g., ProPEX) and then shrink back tightly around the fitting, creating a strong, leak-proof connection without the need for crimp rings or clamps on the outside of the fitting.
Why the other options are wrong
- A. PEX-c is manufactured using the electron beam (radiation) method, not the Engel process. PEX-a is made with the Engel process.
- B. PEX-a is generally the most flexible, not the most rigid. Burst pressure ratings are similar across types when properly rated.
- C. PEX-a is generally considered the most flexible and is widely used for radiant heating, though other types can be used.
PEX Types (a, b, c)
PEX (cross-linked polyethylene) tubing comes in three main types (a, b, c), differentiated by their manufacturing process and resulting material properties, affecting flexibility and fitting compatibility.
- PEX-a: Engel method, most flexible, shape memory, expansion fittings.
- PEX-b: Silane method, good flexibility, crimp/clamp fittings.
- PEX-c: E-beam method, least flexible, crimp/clamp fittings.
Memory trick: PEX-a's Amazing Ability: Always Auto-Adjusting.