Testing gas pressure

studio54

Hi
Can anyone with "expertise" give me a reason why it is incorrect to check gas standing pressure at the gas valve of a boiler as opposed to the gas meter when carrying out a soundness check on a line?
Regards
PS I am RGI registered

wilser

Never knew it was incorrect myself, just find it handier to do at the meter.

studio54

studio54 wrote: »

Hi
Can anyone with "expertise" give me a reason why it is incorrect to check gas standing pressure at the gas valve of a boiler as opposed to the gas meter when carrying out a soundness check on a line?
Regards
PS I am RGI registered

Usually you would have your u guage on at the meter when doing your test and standing pressure would normally be looked for at that point when discussing standing pressures, I would guess that's why your being told that.

Who told you it was wrong.

Standing pressure is standing pressure and can be taken anywhere you just clarify it by stating where the reading was taken from, there is no wrong place.

shane0007

As Gary says, standing pressure will be exactly the same throughout the system.

What you must check is the working pressure at the meter & working pressure at the appliance as a maximum loss from the meter to the appliance is 1mbar.
Many mistakingly think 19mbar is the minimum at the appliance but if the working pressure at the meter is 21mbar, the appliance WP must be 20mbar or above.

anuprising

gas pressure is affected by volume and temperature . you have no way of knowing the volume in the pipework when it leaves the meter and enters the house . its for this reason you measure at the meter . this is the precise measurement and can be proven . too many varibles at other points .

standing pressure tells you nothing other than there is gas present and the regulator is doing its job ,again this is why you measure at the meter ,nearest to the regulator ,before it enters your pipework .

everything has to be proven . measuring at the boiler or appliance is not the correct way .

operating pressure is another thing all together .

hope this helps

anuprising

anuprising wrote: »

gas pressure is affected by volume and temperature . you have no way of knowing the volume in the pipework when it leaves the meter and enters the house . its for this reason you measure at the meter . this is the precise measurement and can be proven . too many varibles at other points .

standing pressure tells you nothing other than there is gas present and the regulator is doing its job ,again this is why you measure at the meter ,nearest to the regulator ,before it enters your pipework .

everything has to be proven . measuring at the boiler or appliance is not the correct way .

operating pressure is another thing all together .

hope this helps

If you take your information from anything aimed at general gas workers it agrees with you on the first point but if you read anything directed at gas service engineers you will find it goes in to more detail and informs us that the pressure is equal across the installation pipework, this is useful to gas service engineers who are trying to achieve different things to general gas workers.

When I want to see the impact of the standing pressure on a appliance I take it from the appliance this reading has never been wrong.

anuprising

you are wrong gary

I agree that the pressure in theory should be the same across the system under no load from appliances .

but if you test at the appliance and there is a leak before that point the regulator could be pulsing to compensate for the leak and regulating the pressure so you think its normal .
if you test at the meter like you are instructed to do you will hear the regular pulsing . you should have been at the meter to do a soundness test anyway .

its half assed of a service engineer not to confirm the pressure at the meter as he could be leaving a leak behind him . I know he is not liable for that .but good practise .

the op asked why it was wrong and that is why it is wrong and he was probably getting an annual audit .that's why they want you to do it a particular way so you can prove everything . standing pressure cannot be proven by testing at the appliance alone ,it has to be done at the meter .
a service engineer only wants to check standing pressure at an appliance to prove the gas is there .

anuprising

anuprising wrote: »

you are wrong gary

I agree that the pressure in theory should be the same across the system under no load from appliances .

but if you test at the appliance and there is a leak before that point the regulator could be pulsing to compensate for the leak and regulating the pressure so you think its normal .
if you test at the meter like you are instructed to do you will hear the regular pulsing . you should have been at the meter to do a soundness test anyway .

its half assed of a service engineer not to confirm the pressure at the meter as he could be leaving a leak behind him . I know he is not liable for that .but good practise .

the op asked why it was wrong and that is why it is wrong and he was probably getting an annual audit .that's why they want you to do it a particular way so you can prove everything . standing pressure cannot be proven by testing at the appliance alone ,it has to be done at the meter .
a service engineer only wants to check standing pressure at an appliance to prove the gas is there .

I'm not going to argue with you, I'll just agree to differ.

corkgsxr

Its just easyer at the meter. But can be check anywhere.

shane0007

You would never check standing pressure without doing a let by & soundness test first.
So, if you checked standing pressure at the meter & at the appliance, if there was a fault or leak, the result would be the same.
Standing pressure test is only confirming the regulator is functioning, giving equal pressure both sides of the regulator diaphragm. Working pressure at the meter will determine it is maintaining a constant delivery pressure over a range of loads.

studio54

PASCALS LAW......Every plumber/fitter should understand this! Pressure in a closed container/loop is constant. Therefore testing "standing pressure" is equal at all points in container/loop (under constant temperature). I hear a lot from "authority" that it should only be done at meter.

I dont agree unfortunately with the compensation through pulsing idea as to do this would involve sudden peaks and troughs in the pressure of the gas being forced through the regulator to achieve or result in compensation. Under "standing pressure" there should be no losses to compensate for!

The idea behind testing from the meter actually originates from "point of use" hence if a test is being performed from the meter it is under careful watch of the operative that no one can interfere with the isolation valve and any interfering with the line further down will likely result in a drop as opposed to a rise in pressure.....Thoughts?

Thanks for all contributions

anuprising

studio54 wrote: »

PASCALS LAW......Every plumber/fitter should understand this! Pressure in a closed container/loop is constant.............

pascals law applys to fluid only not GAS .............every plumber /fitter should know this

gas is compressable



I really hope the next generation forgive us ............

studio54

Cheers Anuprising for comments....I stand corrected. I hope i didn't appear dismissive and I take your point but my reason for asking all your thoughts is because this is how it has been relayed to me by instructors who, I feel, give a textbook answer when I question them and deflect when I pursue a mathematical explanation.

I still struggle with your theory "pulsing" though. We are talking about standing pressure aren't we? And is a meter/governor not a form of NRV? meaning a pulse in one direction = an increase in pressure in that direction only. Therefore would your theory not mean a constant visible increase in pressure eventually matching pressure before the governor. Also can a gas' pressure be increased at one part of a closed container at constant temperature and not have an effect on the other end?

I am open to being persuaded by you if I could find a mathematical explanation.

And I will say this, if you can prove your theory (and this is totally at your discretion) then their could be a potential entrepreneurial idea for retro fitting gas meters around the country......or have we been here before???:D:D:D

Thanks again

corkgsxr

anuprising wrote: »

pascals law applys to fluid only not GAS .............every plumber /fitter should know this

gas is compressable



I really hope the next generation forgive us ............

Gas is still constant over the whole line otherwise we would have to test every few metres. How can you find leak at the end of the line if pressure isnt constant across the line.

I really cant believe this is a argument.

You could do a pass test and then soundness test at the end of the line it just creates running back and forwards.

anuprising

getting out of hand now , I didn't say it was a way of findinging leaks , there is other methods for that ,. the question was why are we told to do a standing pressure test at the meter only . the reason is its the only 100% provable point on the system that is acceptable . they ate variables with all other points so this is the chosen one by our regulation makers .
I will add more to this tonight

studio54

I feel these questions are needed to be asked as I personally find that all too often the answer from my peers tends towards "you just do" and I worry that adopting this approach leads to "because he told me to" type answers. This may be acceptable (as long it is not followed by "your honor") to most but I prefer to know what are the principles behind why we carry out certain procedures. Surely this is why our industry tends to meet a lot of "chancers". What percentage of plumbers/fitters would attend courses if the state was not paying.

shane0007

Standing pressure can be taken at any point of a system because gas is NOT flowing & therefore there is no resistance applied to the pressure due to the pipework itself or the pipework fittings. It will be the same throughout the installation.
When has is flowing, the gas will meet resistance from pipework, fittings & bends & therefore there will be an exact loss in pressure over the system. This loss can be calculated pretty much exactly depending on the bore of the pipe, fittings & bends to within immeasurable amounts on a standard non-digital gauge.

At the meter does not magically eliminate temperature conditions.

Meters do not pulse either. The work on the principle of equal pressure of spring based tension on a diaphragm for both sides of a governor.

corkgsxr

What if you had a sunny/cloudy day or intermittent wind that you couldn't get a settled pressure? You'd have to move inside for a accurate test

studio54

corkgsxr wrote: »

What if you had a sunny/cloudy day or intermittent wind that you couldn't get a settled pressure? You'd have to move inside for a accurate test

Temperature dependent.....pv=co

corkgsxr

studio54 wrote: »

Temperature dependent.....pv=co

Ever have a day where sun keeps coming out and going back in. Or intermittent wind. It puts out readings. You have to have a constant temperature for constant pressure

Dtp1979

corkgsxr wrote: »

Ever have a day where sun keeps coming out and going back in. Or intermittent wind. It puts out readings. You have to have a constant temperature for constant pressure

Hate those days!