Worcester Expansion Vessels (Page 3)
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 87154072960 Expansion Vessel - 7L - EMS Combi/Classic/Danesmoor
Part No: 1013107 / MPN: 87154072960