Expansion Vessels and where to put them?

[Mike2007]

I have never understood why expansion vessels are put high in the system design, where the diaphragm will be subject to the higher water temperature and the vessel is lightly to gather air??
Surely lower would be better in a sealed system and avoid these possible problems?

 

[polesapart]

They are put high up for convenience only. Optimally they should be plumbed in at a height where no air is trapped against the diaphragm on the system side.
This extra air cushion seems in practice to make no difference whatsoever -look inside any combi or system boiler - most, if not all- will have the water connection at the bottom and must trap air on filling.
An argument for bottom connection is sediment and system debris.

Of more importance is access to the Schraeder valve.

 

[Mike2007]

They are put high up for convenience only. Optimally they should be plumbed in at a height where no air is trapped against the diaphragm on the system side.
This extra air cushion seems in practice to make no difference whatsoever -look inside any combi or system boiler - most, if not all- will have the water connection at the bottom and must trap air on filling.
An argument for bottom connection is sediment and system debris.

Of more importance is access to the Schraeder valve.

So saying that, mid-point between the system vents and system drains would be best. Allowing for access as well?
Solar PV's are meant to be installed inverted, strange how they differ?