Can C/H expansion pipe be under the surface in feed tank?

[foggy]

Whilst bleeding my heating system after removing a rad, I got to idly wondering if there is any reason why the expansion pipe doesn't go below the surface of the water in the feed tank. This would prevent any air being drawn back down it, but wouldn't cause any restriction to the expansion of the water - or would it? And any air expelled from the pipe would just bubble up to the surface. Or would there be some problem with a siphon effect that I haven't thought about?

I know it works fine as it is, but I've got an enquiring mind...

 

[Onetap]

It shouldn't be, you'd get water circulating through and heating the tank and oxygenated water going into the system.

That is a common cause of cold water storage tanks getting hot, due to heated water rising from the HWS cylinder.

 

[foggy]

Thanks for the prompt reply, that explains everything. I knew there would probably be a reason for it.

 

[bathjobby]

Exactly as onetap says, plus constantly re-oxygenating the water will corrode your entire system in no time (rust feeds on oxygen). Thats why the system treatment additives (amongst other things) de-oxygenate the water.