Chris B wrote:

On 03/03/2020 23:33, Mathew Newton wrote:
On Tuesday, 3 March 2020 21:50:42 UTC, Chris B wrote:




Original plumber has agreed to come back and do the work described as
required by the tank manufacturer, but having looked much more into how
these systems work I thought that a small expansion vessel would also be
needed in addition to the PRV.

No expansion vessel is required on the cold as there's no expansion to
accommodate. The only reason is it required on the hot side is due to
the expansion that arises from heating the water.


I understand why a large expansion tank is required to accommodate the
expansion of 200lt of water as it is heated from say 5C to 60C.

However on the cold side the entire volume of the cold supply pipe
inside the house (2 or perhaps 3 litres) will be warmed from 5C to house
ambient - say 20C. This must cause some expansion (volume increase may
only be an egg-cup full) and I am curios as to how this is dealt with.

I could invent a hand-wavy explanation about cold taps never being off
long enough, or leaking a bit at high pressures, but the fact is that
people (including me) put double check valves in cold supplies with no
ill effects. And no expansion vessels.

--

Roger Hayter