Booster pump for mains water, no break tank?

[Archibald Tarquin Blenkinsopp]

This seems ridiculous and illegal. Is there something I'm missing or is it acceptable to put your neighbours into a negative water pressure scenario?

AB

[Tim+]

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.

Tim

[Archibald Tarquin Blenkinsopp]

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.

AB

[Fredxxx]

Why? Once you got minimum flow the pump would cut in and flow would increase, not go down.

I think that is the point the OP is making, where this pump could draw a vacuum in the suppliers pipework.

That is the issue. If a neighbour turned on a tap, air could be drawn into the suppliers pipework.

[Archibald Tarquin Blenkinsopp]

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.

AB

SNIP

[Fredxxx]

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!

[Archibald Tarquin Blenkinsopp]

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 cess pits.

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 :-)

AB

[newshound]

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.

[Archibald Tarquin Blenkinsopp]

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!

AB

[Roger Hayter]

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.

[Andrew Gabriel]

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.

[newshound]

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.

[dennis]

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.

[Roger Hayter]

Like an electric shower - not a rare item.

[David]

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 smaller bore).

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.

Cheers

Dave R

[Roger Hayter]

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.