On Fri, 15 Dec 2017 22:34:16 +0000, Johnny B Good wrote:

====snip====


So, my questions a

Is my current header tank feed and expansion pipe arrangement something
to be concerned about?


Having posted the original fulsome query. It's occurred to me that the
point at which the overflow has been teed into the system is on the
suction side of the pump which should make "pump-over" impossible.

Considering that the feed pipe from the header tank is likewise
subjected to the same drop in pressure during pumping, there may be a
small but transient 'draw down' from the header tank during pump startup
with a corresponding small but transient back-flow when the pump shuts
off.

Ignoring evaporation of the header tank water for the moment, the first
draw down event will cause the ballcock to admit a little water to top it
back up, thereafter, the level can vary without further admission of top
up water. Since header tank water does evaporate, the ballcock will
eventually operate to compensate for this loss.

Although the net effect on water consumption remains unchanged, the same
can't be said for the corrosion inhibitor which will suffer a marginally
higher rate of consumption, particularly of its anti-oxidant component as
it becomes dispersed into the header tank where it can then be consumed
by the dissolved atmospheric oxygen. The 3 or 4 metres of 15mm pipe
between the header tank and its connection into the system plumbing will,
however, act as a buffer zone with an inhibitor concentration gradient
that will reduce the diffusion rate of inhibitor into the header tank.

I suspect I may be "over-thinking" this conundrum. Feel free to respond
to this post rather than the previous one (it'll make quote trimming a
doddle :-) ).

--
Johnny B Good