let by + gas leak

[johnnyplumb]

Afternoon all, a wee experiment for you all to try
you'll need the tools shown in the picture above


connect your manometer to the meter and set gauge to 10mb as if doing a let by test,
now create a small gas leak, I've used the bellows with it's valve slightly open to do this,
now you want to create a small let by on the ecv to compensate for the gas leak.


What you want is your gauge to stay at 10mb,
so now you've got 2 faults, ie a let by + a gas leak and the manometer reads as if all is well


now you want to use the bellows to increase the gauge pressure to 20mb
[ dont touch the ecv or the bellows valve at this point, as you dont want to alter the let by or the gas leak you've created ]
now do a tightness test 20mb for 2mins


I did the tightness test a few times and I was getting a drop of between 2 - 4 mb


what's the point of all this nonsense,
well the powers that be, say it's alright to leave a 4mb drop [u6 meter] on an existing gas supply with appliances & no smell of gas etc.


if you do this in the experiment i've created, you'd be walking away and leaving a let by as well as a gas leak


so what can we learn from all of this, well, if you get an 'allowable' permissable drop, dont walk away from it, until you've checked for some sort of drop at 10mb as well,
if there's no drop at 10mb, it's likely that the ecv is letting by.

 

[Pssst]

I dont have any accouterments on my water guage. Just a tube direct to the meter.

 

[Billy Bob Bob]

if you leave your gauge and hose in the sun the equipment and gas inside it will expand,it will rise by atmospheric pressure and will show a rise in pressure

 

[lame plumber]

not done in controlled conditions so doesnt actually prove anything, as gasman said solar and wind cooling could have a major effect as well

 

[johnnyplumb]

if you leave your gauge and hose in the sun the equipment and gas inside it will expand,it will rise by atmospheric pressure and will show a rise in pressure

it was'nt in the sun that long

the gauge was'nt rising either and at 20mb it was dropping.

here's another question for you then,
why do you think we do a let by at 10mb but a tightness is done at 20mb ?

 

[lame plumber]

just think and the answer is obvious

 

[Billy Bob Bob]

just think and the answer is obvious

i wasn't going to grace a answer

 

[tamz]

Regards the sun having an affect. It really can do and can hide a drop.
Next time you test an inside meter with an electronic gauge where the temp is pretty stable stick your hand on the pipe and see how much it rises from the heat of your hand.

 

[johnnyplumb]

i know what you mean tamz, but what can you do, the sun always shines in glasgow :sunny:

 

[johnnyplumb]

i wasn't going to grace a answer

the thing is, the answer to that question has a real relevance here, but my findings are showing otherwise.
it's only when the drop is 4mb or less, that a let by may go unnoticed. any drop above 4mb would fail a tightness test anyway, then the problem would probably be found.

i'm gonna try this again under different conditions, we'll see what results i get.

 

[rab250]

Try it with lpg.

 

[Billy Bob Bob]

the thing is, the answer to that question has a real relevance here, but my findings are showing otherwise.
it's only when the drop is 4mb or less, that a let by may go unnoticed. any drop above 4mb would fail a tightness test anyway, then the problem would probably be found.

i'm gonna try this again under different conditions, we'll see what results i get.

ok lets see what it throws up

 

[leethegasman]

if you leave your gauge and hose in the sun the equipment and gas inside it will expand,it will rise by atmospheric pressure and will show a rise in pressure

Had this to day looked like ECV was letting by on my seconded test half hour later but the sun had come out and would not stabilise so covered external pipework with 4 towels stopped the rise and proved no let by.

 

[Pssst]

Just undo the ECV outlet and LDF/gas test it..

 

[leethegasman]

Just undo the ECV outlet and LDF/gas test it..

Thanks I did now to LDF ECV but it was temperature stabalization , the sun would not hide for me cheers anyway.

 

[johnnyplumb]

ok lets see what it throws up

i've done some more tests under different weather conditions etc now, :sad:
I was 99.9% sure about the results before, but now i'm 100% sure.


I've no doubt that the sun can cause a gauge to rise, but that's not what happened here. This time I tested on a few different meters & made sure there was no sun / wind etc :sad:


Here's what I found
It's all about the amount of let by and the amount of gas leak, they obviously both need to be equal, but they also need to be really small to get a drop of 4mb or less.
Create too much of a let by / gas leak, and when you raise the pressure to 20mb, it'll drop quicker than a who-eres drawers.

So there you have it, ignore all of this at your peril

​

 

[lame plumber]

look you dozy so and so, you do the let by first to establish that there is no let by, then when you do the tightness test you know theres no let by affecting any potential leaks. you do the let by at 10 mb and the tightness at 21 mb so there is a reason able chance of spotting the let by prior to tightness test. get it now!!!!

 

[johnnyplumb]

look you dozy so and so, you do the let by first to establish that there is no let by, then when you do the tightness test you know theres no let by affecting any potential leaks. you do the let by at 10 mb and the tightness at 21 mb so there is a reason able chance of spotting the let by prior to tightness test. get it now!!!!

not me that's the dozy one :laugh3:
are you sure your gsr ?

read my 1st post again till it sinks in, then come back with a more sensible answer the next time :confused5:

 

[lame plumber]

1000s of people doing tests and you try and set up a situation to get yourself worried, keep on worrying, no one else is.

 

[johnnyplumb]

1000s of people doing tests and you try and set up a situation to get yourself worried, keep on worrying, no one else is.

i'm more worried about your lack of knowledge :lol:

 

[lame plumber]

i'm more worried about your lack of knowledge :lol:

The lack of knowledge and basic physics is on your side dont embarass yourself any further