This seems ridiculous and illegal. Is there something I'm missing or
is it acceptable to put your neighbours into a negative water pressure
I used to think so too but I suspect that it must monitor pressure on the
inlet and throttle back or cut out if the pressure drops too low.
Otherwise, as you say, it could be sucking crap into the pipework.
Trolls AND TROLL FEEDERS all go in my kill file
I just cannot understand how it could function properly, it would just
cut in & out like a machine gun surely?
I presume supply pipes need to be kept under positive pressure anyway
in order to keep the crud out if there are leaks. Thames were renowned
for the cullender like qualities of their pipework.
If one of these were placed at the bottom of a dip, there may still be
quite a bit of pressure if one of thoe living further up the hill
turned on their tap. I know none returns are the norm now and they may
stop air flowing back to the main, but I'm sure most houses just have
a straight feed to the stopcock and first tap.
I was replying to the suggestion that too low a pressure on the
suction line would cut the pump.
This would avoid pulling in of water from a neighbours system, but as
the pump is specifically designed for low flow situations, this would
then mean that the pump energises, flow increases and suction pressure
drops. The pump would stop and the pressure would build up starting
the cycle again.
There must be a market for this pump, and I assume it's practical and
legal. I just don't uderstand how though.
On 07/08/2016 19:08, Archibald Tarquin Blenkinsopp wrote:
I had assumed that if there was a 0.6 l/m flow without the pump running,
the flow could only increase when the pump runs.
Many moons ago I lived in a house where at certain key times of the day
the flow out of the shower would be nothing more than a trickle. Perhaps
rather selfishly, with this pump I could have a pleasant shower at the
expense of my neighbours flow rate!
Might have a few interesting little additions to the shower gel if the
water was run through leaky pipes in the vicinity of equally leaky
There is also the possibility that if a neighbour had suspicions that
you were taking an unfair portion, they may park a gallon or two of
fountain pen ink under their tap for periods of negative pressure :-)
On 8/7/2016 11:51 AM, Archibald Tarquin Blenkinsopp wrote:
Why do you think this might be the case? Stuart Turner is a reputable
firm which has been in the business forever and I suspect that they do,
actually, know about water regulations.
ISTR that Stuart Turner are regenerative pumps, and my brain hurts when
I try to understand how they work.
Thanks, I see it all now!
I assumed it was a standard centrifugal pump!
I would imagine there were very very few circumstances where these
pumps could be successfully employed on an authourity produced
domestic supply though.
Thanks for that!
It seems fairly clear that the pump control system prevents it from
reducing the pressure at the intake below a low positive pressure. An
unregulated pump would presumably increase the flow from the mains, but
this one is clearly controlled to avoid increasing the flow rate beyond
that which is already available at low pressure. Say that the mains
water pressure is 2bar but as soon as a tap is turned on the pressure
starts to fall, and a maximum of 6 litres per minute flows with a fully
open tap and a drop of 0.05 bar between the service pipe at the tap.
If you connect this pump it will regulate itself to deliver a maximum
flow a little below 6litres per minute but at an outlet pressure of
1.5bar. So you *can* use a shower, but only at the pitifully low flow
rate you originally had.
So it doesn't increase the water flow available, but does deliver it at
a more useful pressure. At 1.5 bar the main supply would probably only
deliver about 1 litre a minute, which would be even less useful.
That doesn't make much sense to me.
The only way to increase the pressure in that scenario would be to
restrict the flow even more after the pump so it can do some work in
increasing the pressure.
About the only use I can think of is if you bought something that needed
1.5 bar to work but didn't need any more flow.
I downloaded the datasheet (which is rather sparse on this point).
It implies the pump assumes a minimum pressure of 0.7 bar (which is
apparently what water companies are required to provide), but it
doesn't indicate anywhere that this is actually tested by the pump.
[email address is not usable -- followup in the newsgroup]
I have a clever friend who used to design pumps for Stothert & Pitt.
I'll see if he can explain to me what limits the "suck" of centrifugal
pumps operating in water. Is it the same as good old fashioned "lift
pumps", i.e. the lowest pressure attainable is the vapour pressure of
water at the current water temperature?
I can certainly envisage special geometries where you could potentially
starve the supply to a neighbour, which seems to be a bad thing.
However, I suspect that the "impedance" of water supplies is normally
sufficiently low to prevent this happening.
On Sun, 07 Aug 2016 11:51:14 +0100, Archibald Tarquin Blenkinsopp wrote:
As with others, this makes my brain ache.
However, I did consider this:
Assume that the incoming pipe is 2"/50mm diameter; this can support a
reasonable flow rate even at low system pressure.
However once entering a domestic property the pipework goes down to 22mm
or 15mm which acts as a flow control mechanism.
This leads me to think that the natural flow rate of the incoming mains
pipe could be significantly higher than the natural flow rate of the
pipework in the house (at any given working pressure).
So it does not seem unreasonable to attach a pump to the incoming mains
(large bore) and pump to maintain the natural mains flow rate through the
smaller bore pipework.
Think of it as comparable to having a pressure washer connected to an
outside tap (which as far as I can see does much the same thing at a
Water comes in at the hosepipe and is then pumped down a very narrow bore
pipe to emerge at high pressure. You get the high pressure jet without
sucking the hosepipe flat. You also don't use a lot of water - well within
the capacity of the hose pipe.
Further, with most water mains these days powered by electric pumps, I
assume that if you start to suck the local water main dry (and as far as I
know the bore of the local water main is a lot larger than the bore of the
pipe from the main to your house) then the electric pump would kick in to
increase the flow rate.
So looking back further into the system, your booster pump probably has as
much (or as little) effect on the water main as your pressure washer does
on your domestic plumbing.
I think the pressure washer is a perfect analogy, in that if simply does
not reduce the domestic water pressure, it just supplies a fraction of
the flow rate the domestic supply is capable of. And I suspect the pump
in the OP does the same, although the fraction may be up to 95%. It is
just not intended to increase the flow available and I suspect it is
designed to avoid this, for all the reasons, especially backflow, that
people have suggested.
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