What Is an Expansion Vessel?
An expansion vessel is a crucial safety and performance component in heating and potable water systems. Its main purpose is to absorb increases in water volume caused by temperature changes, preventing over-pressurisation that could damage components or cause leaks.
How Do Expansion Vessels Work?
Water reaches its lowest density at 4°C (not 0°C as commonly thought). Above or below this temperature, its volume expands, whether turning to ice or heating up.
When system water expands, it needs a safe space to go. An expansion vessel provides this space via a sealed air chamber with a pre-charge of air. As water volume increases, it flows into the vessel. As the system cools, the pre-charge pushes the water back into the system.
Key factors in vessel sizing:
- System temperature
- System volume
- Safety relief valve (SRV) setting
- Pre-charge setting
- Application type (heating or potable)
