Metal vs Stainless Steel vs Rubber Expansion Bellows

Rubber (EPDM, NBR or Viton) is the default for pump-discharge connections, chiller pipework and any plant-room circuit where vibration isolation matters more than peak temperature. Single sphere up to DN150; twin sphere for larger pumps or longer runs. Use tie rods on unanchored installations to resist pressure thrust.

Metal bellows (often a stainless convolution welded to carbon-steel ends) take over above 110 °C — steam mains, hot oil circuits, flue connections. They also absorb the large axial growth of long heated pipe runs that rubber simply cannot service. Pair with anti-vibration mounts on the equipment because the bellows itself transmits vibration.

Choose all-stainless (321 or 316L) for aggressive media, outdoor installations, high-purity service, or anywhere long-term corrosion resistance drives the lifecycle decision. Multi-ply constructions extend pressure rating and fatigue life for cyclic duty.

Whatever the bellows material, specify flanged ends (PN16 or PN25 to EN 1092-1) when the connecting pipework is flanged. You keep the joint serviceable: it can be unbolted and swapped without cutting pipe, which matters most on pump skids, plant-room headers and isolation valve sets.