How do water supply companies reduce the pressure?

My house supply has a pressure reducing valve, lowering the house pressure to

A random youtube video, there seeem to be many:

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Isn't that pretty much what happens inside a pressure regulator, with the valve constantly automatically adjusted to keep the output pressure at the set point?

nib

So at night with no flow, the pressure reducer valve would have to totally shut off and then how would it start up again or do such systems require some sort of minor leaks in the system.

What happens is that as soon as you start to draw water the valve gets a pressure differential across it that opens it.

Starting up is easy, you draw off some fluid, the pressure reduces, the valve opens just enough.

To accommodate leakage, where with gas you'd have to leak a lot before an over-pressure limit would work, with liquid, an accumulator would do the same thing.

nib

Or, when they don't reduce the pressure

Hence this query. The last few days I'd noticed a different noise at the rising main, when drawing off water. I now know it was due to high pressure. This pm I took some readings off the red 1 Litre per rev dial on the water meter, to check if there was any unseen/unheard leaks in the ground or crawl space, after the meter, no ongoing problem found.

Interesting to wonder if there are any regulations as to what pressure water companies are allowed to supply.

I think it is probably another name for the same thing. Or perhaps I just got the name wrong? But a pressure regulator can only work properly if it is also reducing the pressure from the supply.

I wonder the same. I saw the actual report on local TV last night. Southern Water said they would make 'goodwill' payments of 250 quid to the affected people, saying that the remainder should be claimed from insurance. Cheeky cheeky fookers in my view. They should pay at least

What are the specifications for pressure on say your stopcock, or the stopcock on your street meter ? It's a bit frightening to think that you can't really isolate yourself in such an occurrence ?!

Before my time, but wasn't there a nasty instance of gas over pressure in Royston (Herts/Cambs border) in the 60s, where some people had their cookers suddenly become mini flame throwers ?

Oh, much more recent, 1991 !

By that phrase I mean SW must know their own pipework being suspect. They keep "repairing" breaks in the 4 inch fresh water supply cast iron pipe to our area. The repairs consist of disc cutting out a section and then compression clamping in some blue plastic pipe in the gap. Surely even SW must be wondering why the breaks are 2 metres from sewer system manholes. In the 70s the sewer system was upgraded so 6 inch went to 8inch, 8inch to 1foot and 1foot became half-metre pipes. Leaving all the 4 inch residential piping in place, which means junctions between old and new 2 mtres in from the concrete replacement manholes. With 50 years of settlement, hydraulic pressure etc those unions have failed( captured on CCTV sewer survey). Subsoil and gravel entering the sewers at the breaks and ground cavities forming around the breaks, with the fresh water pipes only 1 metre above the local sewer system. Cast iron piping cannot take deflections along its length. Of course SW does not tell us about the breaks, so at 8am and 6pm with excessive water usage and very low pressure, the chance of sewage groundwater entering the local fresh water supply.

A regulator is a partially closed valve whose closure is determined by the pressure downstream

Most of this thread seems to assume that mains water pressure IS regulated - but I am not so sure.

First thing in the morning, and in the middle of the night, the water pressure around here seems to be noticeably higher, and I assume that its lower during the day due to higher demand.

If I flush the downstairs loo during the day, it takes about 90 seconds to refill and shut off the ballcock - whereas if its done in the middle of the night its down to around 75 seconds, and when it does shut off, its "down to earth with a bump"

I cant think of any reason for this variation other than a change in pressure, which leads me to suspect that maybe during the day the pump system is just doing what it can to keep up with the flow, rather than maintaining a specific pressure.

And then a pressure feedback pipe reduces or increases the pressure on a diaphragm that regulates that downstream pressure. If the valve had closed off when there was no use downstream, when the downstream pressure and the upstream pressure became equal, as soon as the downstream pressure reduces, the feedback loop will open the regulator diaphragm to let water through, until the downstream pressure rises again.

I would imagine (hope) that there would be similar statutory requirements as per gas and electricity supplies.

However, that said, there are also statutory requirements not to pump s*it (the literal kind) into watercourses, and they have f*ck all effect.

And then there's this atrocity in Sussex

Always rely on the BBC to come up with some story worthy of the Doom Pixie herself.

-- “I know that most men, including those at ease with problems of the greatest complexity, can seldom accept even the simplest and most obvious truth if it be such as would oblige them to admit the falsity of conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven, thread by thread, into the fabric of their lives.”

― Leo Tolstoy