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.
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).
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.
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.
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
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.
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.
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.
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?
Or a separate restrictors before each valve - probably just the valve
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.
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