Gas release valve?

What are those things you see in the middle of nowhere (in the UK at least), a 10 foot high white pole with an orange roof-shaped lid on top? I gather they're to release excess gas from the mains and burn it off, but why would that be necessary? Surely they wouldn't put more than the correct pressure in anyway? Any excess could be released at the source at the gas plant? I've never known of one actually operate. I can't find a picture of one on Google as I don't know what they're called. Searching for pressure release just shows domestic valves.
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Commander Kinsey wrote:

Hi-viz poles to allow the chopper to follow the pipeline route easily.
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They're not just markers, I'm sure they can actually let off gas.
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On 11/03/2019 15:46, Commander Kinsey wrote:

They are simple makers for the helicopter that checks the pipeline to follow with its airborne leak checker. One of the high pressure pipelines runs close to me. They also mark the no dig zone at the roadside (permission required from the pipeline owner Ineos or Shell).
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That seems unfair; after a boring day mashing up roadside culverts and the occasional fibre duct, a high pressure gas pipeline would be quite an exciting find for JCB operator.
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Roger Hayter

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On 11/03/2019 16:09, Roger Hayter wrote:

Somebody 'found' the underground fuel line when it ran through the grounds of a large estate, and they dug down, tapped into it and nicked loads of diesel.
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Yeah, the pipeline company never bothers to measure how much product enters and leaves the pipeline, so they'd never notice such a crime.
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I can't tell if that's sarcastic.
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Are you sure? I looked at one once and I'm sure it had some kind of valve in it to let gas out. When I asked someone at the time, I was told that if it had let off pressure and ignited it, the bright orange lid would have been blackened, signifying there had been a problem.
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On 11/03/2019 16:33, Commander Kinsey wrote:

The main pipelines run at some insane pressures & they don't vent. The estimate for the SPL at 100m if our pipeline was breached is 140dB.
https://www.sabic.com/en/about/ehss/sabic-uk-pipelines
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Martin Brown
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I did wonder how they could distribute all that gas at 1.1 bar. I guess there's a lot of complicated valves somewhere to change the "voltage" as it were? Do they ever fail and put high pressure into the final piping? I dread to think what would happen if the "insane" pressure got into your boiler.
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There are pressure reducing meters at pretty much every point-of-use which reduce the line pressure to a pressure compatible with standard appliances; you may notice that some meters have a much smaller inlet pipe than the outlet pipe (e.g. commercial premises) due to the need to for more volume at the lower pressure.
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So the meter outside my house reduces the pressure? I thought the pressure was lowered for the whole street, like a substation reduces the electricity to 240V.
I had noticed on older houses there's some kind of valve seperate from the meter (often exposed to the outdoor weather!), presumably nowadays it's inside the meter.
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On 11/03/2019 18:49, Commander Kinsey wrote:

Your meter has a regulator that drops from an already lowish pressure to 20mbar.
http://www.gasinfo.uk.com/distribution_page.htm
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Wow, 20mbar is damn low, I'm surprised that has the desire to move along the pipe.
How do things like camping stoves work? I assume the pressure inside a butane cannister is much higher than that, and I don't think they have pressure reducers.
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On 11/03/2019 20:25, Commander Kinsey wrote:

I presume that the needle valve and feed to it is sized to be very restrictive for the simple screw on burners.
The bigger ones fed by hose from a Calor cyclinder or the like have 28mBar regulators for butane or 37 mBar ones for propane. The different pressures allowing for the different calorific values of the two gases when using the same size jets, so allowing interchanging bottles depending upon the ambient temperatures. Butane won't gas off from the liquid on a cold day.
With high flows, such as a water heater (my parents' one needed a regulator capable of 4kg of per hour), the boiling off of the gas can cool the bottle too much and reduce gassing, so even in the summer, they had to use two butane bottles in parallel or a single propane one.
SteveW
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For example, I have a twin burner (Tilly) stove. It's fed from a butane cannister. Since I could operate one or both burners at different rates, there can't be a limiter anywhere that could work unless it's clever enough to adjust pressure independant of flow rate. Perhaps the pressure is quite high, but the taps to control the burners are what restricts it?

I wasn't aware of that, so I can't use a butane camping stove in winter?

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On 11/03/2019 21:26, Commander Kinsey wrote:

Or a separate restrictors before each valve - probably just the valve design though.

Basically correct. You may get away with it, but when temperatures are down to about 4°C, the cylinder cools a little further as the gas is used and it gets the bottle too cold to boil any more gas off. It is not actually a sudden cut-off, it is a reduction in the rate of boiling and so the gas flow is too low for the burners.
SteveW
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I didn't know that. I've never used a stove in cold temperatures. So anyone camping in winter uses propane?
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On 11/03/2019 22:59, Commander Kinsey wrote:

Yes, you have to. Otherwise no cooking or heating when it's cold.
Bill
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