What are the differences in thermal expansion joints required for PVC versus polyethylene?

Thermal expansion joints are critical in plastic piping systems to accommodate temperature-induced dimensional changes. PVC (polyvinyl chloride) and polyethylene (PE) have distinct thermal expansion properties, requiring different joint designs.

PVC has a lower thermal expansion coefficient (approximately 5 x 10^-5 per °C) compared to polyethylene (ranging from 1.5 x 10^-4 to 2 x 10^-4 per °C). This means PE pipes expand nearly 3-4 times more than PVC under the same temperature rise.

For PVC, expansion joints are typically spaced farther apart (e.g., every 100 feet) due to its lower expansion rate. Polyethylene systems require more frequent joints (often every 30-50 feet) to prevent buckling.

Installation methods also differ: PVC often uses rubber-ring or solvent-welded joints with allowance for movement, while PE systems commonly incorporate looped expansion joints or specially designed couplers.

Understanding these differences ensures proper material selection and installation for durable, leak-free piping systems in various temperature environments.