Worcester Expansion Vessels
The expansion vessel is a small chamber that is used to protect closed heating systems from pressure surges. The pressure vessel is filled with air that acts as a cushion against surges in pressure within the system.

Worcester Bosch 87161425030 Mini Expansion Vessel - Ha50 - 24i/28i
Part No: 1018305 MPN: 87161425030

Worcester Bosch 87161425020 FSN Expansion Vessel - 8Ltr 389 Diam - 24i/28i/30i
Part No: 1018303 MPN: 87161425020