HAMWORTHY HEATING LTD
3
WEYMOUTH
500001112/C
Figure 3 Typical System Schematic Layout
3.2 Application
The system expansion vessel charge pressure is set 0.1 bar below the cold fill pressure. Before operation of the
boiler, with the system at cold fill pressure the expansion vessel is empty . As the system heats up the expanded
volume is absorbed by the expansion vessel. A small pressure rise occurs which is accommodated by the vessel.
When the system cools the pressure drops. If there has been some fluid loss the pressurisation provides
replacement.
Figure 4 Expansion Vessel Operation
1. Diaphragm position at the cold fill / charge pressure. The vessel is empty of system fluid.
2. Diaphragm position at the hot working pressure. The system volume has expanded due to the temperature rise. The gas in the vessel is
compressed. Acceptance factor = 0.35 maximum (recommended).
3. Diaphragm position at high system pressure. The boiler system is shut down by the system pressure switch on Advanced Unit.
4. Diaphragm at the safety valve lift pressure. Caused by boiler temperature limiter failure for example. Acceptance factor = 0.5 maximum
(recommended).
