I've been biting my tongue for far too long .. lol .. :-)
Out of interest, accumulators were first used to dampen the effects of
piston pumps by maintaining a steady flow and combating the effects of
'water hammer' - the latter being quite able to burst through an elbow after
a period of time or blast off a poor connection in the pipeline. They
seldom, if ever, had a diaphragm in those days and, unless the discharge
head was very high, were never pressurised.
Adrian's assertation that there is no water exchange in his 'cul-de-sac'
would only work if there is an inverted 'u' in the piping, immediately prior
to his accumulator. Even in small bores (and I'm guessing that his water
piping is likely to be around 15mm - which isn't 'small' in that sense),
there is still likely to be some water exchange due to thermal differences.
The fresh water in the tank is no more, or no less, 'saturated' with air
than the water in the pipes (why should it be different - unless it was
passed through a de-aerator along the way?
When the water is compressed it <may> take in a <minute> part of the air in
the accumulator but, as soon as the pressures ('air' pressure and 'water
vapour' pressure) stabilise, no more air will go into the water - and we are
only talking a few molecules here in any case. I would also hazard a guess
that, unless a lot of water was being pumped in any one period, there would
not even be enough time for a complete exchange to occur - in either
direction.
Open a tap and that <extra> air would be released straight back into the
accumulator (as when you open a bottle of pop) - but the volume of the
exchanges, in the sizes of systems common in small craft, would be almost
immeasurable.
This assumes, naturally, that there are no noticeable temperature changes in
the system and that the tank, pump, accumulator and the piping between them
are sitting at the same ambient temperature.
Trevor [now retreating back into his hole!]
