On Thu, 23 Sep 2004 08:58:21 +0100, Andy Hall
wrote:

On Thu, 23 Sep 2004 08:48:41 +0100, Malcolm Reeves
wrote:

On Wed, 22 Sep 2004 21:46:23 +0100, Andy Hall
wrote:



There may not then be enough
flow through the boiler to remove the residual heat after it stops firing.
How do you ensure that this doesn't happen?

How does a bypass remove residual heat? For that the pump has to run
so you need pump overrun not bypass. However, you may need a bypass
and pump overrun to cover the situation of all rads with TRVs (which
you shouldn't have) and needing to get rid of some heat (to the pipe
work presumably).

How would the bypass operate without a pump?

That's not my point, which was pump overrun is what you need to get
rid of boiler excess heat.

Bypass does not figure, except that you need to allow flow. You could
have an always on rad for that. You always need to allow some flow,
during normal firing primarily so if you have that you have it during
overrun to.

You can use an automatic bypass purely to take care of the over-run
case.

Are we taking about the same sort of automatic bypass, i.e. pressure
driven or is this an electric bypass? As I fail to see how a pressure
bypass can handle overrun without first handling the run into closed
TRVs first.

If TRVs are open, stat goes off, boiler goes off, pump goes to over
run then water will go to rads (or cylinder).


--

Malcolm

Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK
, or ).
Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power
electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see:

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