Material Selection: EPDM vs Stainless Steel Bellows
For the majority of UK commercial chilled water applications, EPDM (Ethylene Propylene Diene Monomer) rubber bellows are the preferred solution. Their primary advantage is the ability to absorb multi-directional movement while simultaneously providing acoustic isolation—a critical factor when pipework is connected to high-frequency vibratory loads like centrifugal chillers or primary pumps. UKGP Industrial rubber bellows are commonly specified with high-tensile synthetic cord reinforcement to maintain structural integrity under pressure.
Stainless steel bellows, designed to BS EN 14917, are reserved for applications where temperature extremes or chemical compatibility exceed rubber limits, or where ultra-high pressure ratings are required. While metallic bellows offer superior longevity in outdoor environments subject to high UV exposure, they lack the inherent damping qualities of elastomer joints. In CHW systems with high glycol concentrations or specific corrosion inhibitors, material compatibility with the bellows liner must be verified to prevent premature embrittlement.
- Standard operating range: -10°C to +90°C.
- Inherent vibration attenuation properties.
- Resistance to common CHW additives (Ethylene/Propylene Glycol).
- Maximum working pressure typically 16 bar (PN16).
Frequently asked questions
What is the difference between axial and lateral expansion?
- In CHW systems, axial bellows are used for straight runs, lateral for offset movements (often at building joints), and angular for rotation. Universal joints combine these to handle complex multi-planar movements.
Why are anchors critical for expansion bellows?
- Primary anchors must be sized to withstand the full pressure thrust (area x pressure) plus the stiffness force of the bellows, often reaching several tonnes of force even in DN100 pipework.
Can I use EPDM bellows with glycol additives?
- EPDM is the standard for CHW due to its resistance to glycol and temperature stability, but NBR (Nitrile) should be considered if there is any risk of oil contamination in the system.
What is the expected lifespan of a rubber expansion joint?
- Standard EPDM bellows typically have a shelf life of 5-10 years depending on UV exposure and ozone levels. In operation, fatigue life is determined by the number of thermal cycles, usually rated for 5,000 to 10,000 full cycles.
When are internal liners required?
- Internal liners (sleeves) should be used in high-velocity systems (typically >5m/s for water) to prevent flow-induced vibration and erosion of the bellows convolutions.
