I have a Myson CH pump and I have a question regarding pumps in general. My
pump has a 3 position switch marked I, II and III this switch just seems to
alter the speed. Is it better to have the pump set at I (slowest) so that
the water passes over the burners slower so heats up more, or set at III
(fastest) so it gets round the system quicker or II (Middle) so it gets the
'best of both'? There must be a reason for the switch or it would just run
at one speed!
Run it as slowly as you can get away with. It's not only quieter but if you
have an open sytem there is less chance of sucking in air or pumping over,
although thos shouldn't happen an a properly designed system.
In 1983 I installed a Myson Unit Three C/H pump. This has a two
position switch plus a mechanical vane for altering the flow. For the
last 22 years the vane has been set to maximum flow and the switch in
the normal position. My system is a solid fuel Bont ESSE room heater
with a water jacket and rated at 12kWatts. The pump is on 24/7 between
September and June/July. I have switched to the high speed position a
few times like when I've used a lot of wood and the water has started
to 'sing'. I just leave it in the high speed position for say 10
minutes and the back to normal. The vane has never been moved.
It would be less efficient like that. The outflow water will be hotter,
which in turn means that the exhaust gas temperature will be higher,
leading to wasted heat.
That said, I would still prefer to run it at a lower speed to keep the
noise and wear down.
Roland Butter :- There\'s nothing like a knob of butter.
If you have a spec sheet for your pump, you will see that you get 3
different pressure vs flow performance curves - one for each speed setting.
This enables you you select the appropriate setting for your system.
Assuming you have a non-condensing boiler, UK heating systems are usually
designed to run with a 10 or 11 degC temperature rise (typically 70 - 81)
through the boiler, and a corresponding drop through the radiators. Run the
pump too fast and the rise/drop will be lower. This is not too disastrous -
but will probably make more noise than necessary. Run it too slowly and the
rise/drop will be more - with the result that the radiator heat output will
be reduced, and you may get some condensation in the boiler if the return
water is too cool - which is *bad*.
So it's best to choose whichever speed gets you nearest to your target 10 or
11 degrees *after* the radiators have been correctly balanced.
Instructions for my system boiler say to balance the temperatures across the
radiators, and then reducing the flow by closing a valve on the main flow
from the boiler to get the correct differential across the boiler, leaving
the pump on maximum setting. Presumably this is to keep flow (via the
internal bypass) through the heat exchanger up to spec.
I have doubts about it improving boiler efficiency. It seems a strange way of
going about it to me. Can anyone explain the rationale for doing it this way?
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