High temperature fluid in the expansion vessel for long periods has the effect of shortening its useful life - ultimately causing premature failure of the diaphragm.
To avoid this situation, an additional "flow-through" expansion vessel is recommended when the fluid volume between the collector and the expansion vessel is approx. 50% or less than the 'wet' side volume (between the expanded diaphragm and the vessel inlet). This approach is covered by European directive VDI 6002. There are two possible solutions that can be employed.
- Where space is not an issue, the ZILMET VSG type intermediate vessel can be used. They have inlet/outlet connections and are installed before the main expansion vessel, or
- The Solarplus Safe range which provides a new and comprehensive solution - especially where space is at a premium. The SolarSafe combines a primary high specification Solar Plus solar expansion vessel with a VSG solar inline vessel, reducing the amount of space required by 40% and the time taken for fitting by 50%.