I was recently told when a plumber cut off a dead leg in our gas pipework that we had a small (but allowable) leak in our system.
Clearly he wasn't wild about chasing the leak but I'd rather there wasn't one. Before I start hunting, what's the acceptable leak level in mbar/min?
Tim
I don't know the answer, but is that the only way to measure leaks - in mbar/min?
If so, surely that makes the max permissible *absolute* leak rate (gms/min, or whatever) a function of the volume of your pipework. Is that's what's intended?
For pipework it's no observable drop, which IIRC is stated somewhere to be less than 0.25mbar (over 2 minutes test).
If any appliance is connected then it depends on the type (and volume) of the gas meter, but if your CORGI registered installer is testing that his pipework is sound he should shut off appliances so that he's testing only the pipework. If he's canny he'll have tested the installation before he made any changes in which case if there was a slight but acceptable drop beforehand *and no smell of gas* and the drop is no greater afterwards he can probably put it down to appliance drop and leave it like that.
It wasn't so long ago that a gas fitter came and did the old "sucking of teeth" bit when he saw our gas cooker didn't have an isolating valve (which he then fitted).
It took us some time to realise that the odd smell in the kitchen was coming from the back of the unit where he had fitted the valve, which was leaking. ;-)
Fortunately, it just took a bit of working the valve open & closed a few times to get it to seal properly but it's made me a wee bit sceptical about the benefits of all these valves.
We don't have a smell of gas (unlike the time another BG engineer who supposedly had tested our system cocked up) but I've decided to invest in a manometer to see if I can isolate the leak.
On several occasions, I have heard mention (from plumbers) of a figure (something like 4mm or 4mbar over some period or other mentioned), hence my question.
Tim
Just tested the system "appliances isolated" and the good news is that there's no drop. Still no drop with CH boiler connected. A small drop (0.5mbar over 2 minutes) with the cooker & tumble dryer connected.
I rather suspect that these bayonet connections account for most of the leak.
With that pressure drop (& no smell of gas) should I stop worrying?
Tim
A gas tumble dryer ??
There's another kind?? ;-)
Seriously, I wouldn't have an electric one. The gas ones are *way* more energy efficient and at 18 years old now, it's been one of my most reliable appliances. (A White Knight for anyone interested).
Tim
yes, my parents have just had to get rid of theirs, the gas fridge went many years back, care to guess where dad worked?
Since the volume of the pipework+meter is to a first approximation is similar for all ordinary domestic installations, then the pressure drop and time equates to roughly similar amount of gas leakage.
If you reckoned that the volume of the pipe+meter is about 10 litres then
4 mbar/2min is about 20cm^3 per min. That's about about 1/2 an egg cup per min, MAXIMUM when the old appliances are connected and there is NO SMELL of gas.If you have a smaller electronic meter (E6 type) or heavy domestic/light commercial (R5) type then the times and pressures are different.
On large domestic installations and above then calculations are required to work out the permitted leakage limits.
THE PERMITTED LEAKAGE FOR PIPEWORK (new or old) IS ZERO. I.e. less than
0.25mbar/2min on a normal installation. That's less than 1cm^3 per min.
I believe there is only one make. If you /must/ tumble dry then a gas one makes sense.
The message from "Tim Downie" contains these words:
What sort and where from?
I am currently on the lookout for a cheap manometer but so far all I have found are expensive digital types.
Having written the above I thought I had better do another more specific search and while I found a number of U tube manometers some were expensive and it was by no means clear that the cheaper ones could be used to check for gas soundness.
Any pointers would be appreciated (and no I don't want to make one from scratch).
B&Q - about 15 quid.
A Monument one like this one.
Tim
So 0.24mbar/2min is okay? ;-)
As it happens, my pipework seems fine and since redoing my dryer connection, my "appliance leak" seems to have gone too.
Thanks for the info.
Tim
Why ever not? This *is* uk-d-i-y!
I made one years ago by bending some clear plastic tube into e U shape, and fixing it onto a piece of floorboard, with a sheet of graph paper behind it. I think I've still got it somehere!
It happens that Roger formulated :
You only need a bit of clear plastic tube formed into a U shape, clipped to a bit of wood and filled with water.
The message from "Tim Downie" contains these words:
Thanks Tim and Frank.
I think I must be going senile. I had managed to get it into my head that the domestic gas pressure was 80 mbar, not 20 mbar.
Buy&Queue had them recently.
I used a plastic tube(ex home brew syphon) a ruler, tape water and a couple of drops of food dye for years.
I've just replaced mine after 14 years, with an almost identical model. They're about twice the price of electric, but I've saved that many times over on the fuel. It's also 4.7kw, higher than electric ones.
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