Simple F&E explanation required

[MikeAustin]

It is irrelevant what the movement up a 15 mm pipe might be.

Its the increase in depth in the F&E tank which matters! Maybe 300 mm x 450 mm!

The feed pipes get blocked because they are only 15 mm whereas the vent pipes are 22 mm.

Tony

Tony, the relevance to me of how far hot water rises in the F&E pipe is that I need not be alarmed specifically about that - i.e. it is normal and does not necessarily mean that there is a problem with the system. That is the only point I wanted to make. To that extent, the size and shape of the F&E tank is irrelevant. Of course, its size is relevant for other reasons.

 

[gigz]

Practical experience can get you through most of the time, but occasionally theoretical understanding may be necessary.
For example, I was checking how much of the F&E pipe could get hot and I estimated that, for an average system, one degree increase in average water temperature should cause a movement of around 150 mm in the F&E (assuming none goes up the vent). So I should not be alarmed at an F&E pipe that is hot for several metres.
I read that the vent pipe should be a maximum of 150 mm away from the F&E pipe - but I could not find out why. This must be related to my original question. To know why this dimension is given would be necessary if, for example, there were constraints on pipe runs.

I don't know how accurate your calculations are but you seem to have forgotten that the radiators expand as well so most of the water's expansion is accommodated by the increased size of the rads!

Water expansion is 12.7 times that of copper. Steel expands less than copper. The maximum effect of pipe and rad expansion is thus about 8% even if everything is copper. I quoted an estimate of 150mm movement up the 15mm F&E pipe for one degree temperature rise. I actually estimated 161mm but rounded down to 150mm. Knocking 8% off the 161mm makes it 148mm. So actually, the original quote of 150mm seems about right.

Or you could just go down the pub