On Thu, 28 Aug 2003 19:41:49 +0100, "Suz" wrote:




A further question on the same topic.
We have fantastic pressure as far as I can tell. Only the kitchen tap is
directly connected to the mains at the minute and you can turn it full on
without soaking yourself. However I have asked Waterline what the pressure
is, to check everything out for a combi, and am waiting 3 weeks later for
some-one to get back to me...

There is an assortment of information at

http://www.ofwat.gov.uk/aptrix/ofwat.../waterpressure

The key point regarding what the water supplier has to do is

"The DG2 measure is ten metres head of pressure, at the external stop
tap, at a flow of nine litres per minute. This should be sufficient to
fill a one-gallon container in 30 seconds. This level of pressure does
not override the duty to supply water constantly at a pressure to
reach the upper floors of properties. "

The important point is to differentiate between static and dynamic
pressure and flow rate.

The static pressure at a given point is the pressure with no water
flow. If you were to connect a pressure gauge at your kitchen tap
and there is no flow into the house the (static) pressure will be the
same as at the external stop tap. If you then start drawing water
into your house, the pressure at the kitchen tap will drop, possibly
markedly. At the external stop tap and especially the water main,
it may drop a little, but if the distributionsystem is well
engineered, it should not be by very much. The longer and the
thinner the communication pipe from the water main to your kitchen
tap, the greater the pressure drop under *dynamic* conditions will be.
The greater the flow that you draw into your house, the greater the
pressure drop as well.

So this is why it can be interesting to upgrade the communication
pipe, but only if the pressure outside at the main is worthwhile.
You will notice that Ofwat only makes the water suppliers deliver 9
litres/minute at 10 metres head of pressure at the external stop cock.
This is a very poor standard indeed and is probably something that
they can easily meet. It would be just about enough to supply one
shower directly, but not brilliantly, and certainly not two.



This may be a stupid question , but is it possible we would need to get our
mains supply uprated for a combi supplying 2 showers, 1 bath and all the
other usual stuff? I wonder if we have good pressure but a small pipe and
performance can't be measured by the kitchen tap.

What rate are you getting at the kitchen tap?

It is possible that the communication pipe is small and would benefit
from being upgraded. However, this can be expensive to do since you
have to pay. You would really need to have measurements taken to be
sure, but I wouldn't commit to anything in terms of upgrades or boiler
changes until you know where you stand.

How do I check what size
ours is? Sorry I know this is really really basic for you guys, but I know
so little, and am a bit of a give-it-a-go Jane.

You can check the pipe size by using a caliper gauge to measure the
diameter directly or you can wrap a thread around the pipe and
carefully measure the length. Divide by pi (3.14) to get the
external diameter of the pipe.


Ta
Suzanne


..andy

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