Decided to measure the gas consumption of the boiler pilot light, via the
meter test dial, yesterday, within usual range, as reported on the
internet.
Then today I thought I'd see if there was any leak in the whole system.
Turned off the boiler totally just after breakfast and then took readings
every hour. Reading increased about 0.0001 cu ft in first hour and 0.0001 cu
ft in the next 3 hours. Would most of that first hour just be recovering in
pressure over the whole gas distribution system ? Is 0.00003 cu ft per hour
leak acceptable, no gas has ever been smelt by anyone. How much influence
from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for manometer
testing is, ie what mm or no mm of water drop over how many minutes at what
gas pressure, then volume of pipe runs etc to determine it that way. But
neither found.

The message
from "N Cook" contains these words:

I tried googling for that info and also what the criteria for manometer
testing is, ie what mm or no mm of water drop over how many minutes at what
gas pressure, then volume of pipe runs etc to determine it that way. But
neither found.

I can't recall the detail but I am sure it has been aired on this ng in
the past. I usually save such postings but it doesn't seem to be the
case for that information.

Could be in the gas fitting faq. Logical place for it I suppose but I
haven't checked.

http://www.makewrite.demon.co.uk/GasFitting.html


--
Roger Chapman

Roger wrote in message
k...
The message
from "N Cook" contains these words:

I tried googling for that info and also what the criteria for manometer
testing is, ie what mm or no mm of water drop over how many minutes at
what
gas pressure, then volume of pipe runs etc to determine it that way. But
neither found.

I can't recall the detail but I am sure it has been aired on this ng in
the past. I usually save such postings but it doesn't seem to be the
case for that information.

Could be in the gas fitting faq. Logical place for it I suppose but I
haven't checked.

http://www.makewrite.demon.co.uk/GasFitting.html


--
Roger Chapman


If I can't find it there or renewed effort on the net tomorrow , I will have
to look out BS6891, just to find what the observing time is, and assume
0.5mm or 0.05 mbar is the resolvable limit in that time,
work out the volume of 22 and 15 mm pipe , Boyle's law etc to deternmine
what the soundness test means in terms of cu ft / hr as an upper bound

On Fri, 07 Mar 2008 17:23:30 +0000, N Cook wrote:

Roger wrote in message
k...
The message from "N Cook"
contains these words:

I tried googling for that info and also what the criteria for
manometer testing is, ie what mm or no mm of water drop over how many
minutes at
what
gas pressure, then volume of pipe runs etc to determine it that way.
But neither found.

I can't recall the detail but I am sure it has been aired on this ng in
the past. I usually save such postings but it doesn't seem to be the
case for that information.

Could be in the gas fitting faq. Logical place for it I suppose but I
haven't checked.

http://www.makewrite.demon.co.uk/GasFitting.html


--
Roger Chapman


If I can't find it there or renewed effort on the net tomorrow , I will
have to look out BS6891, just to find what the observing time is, and
assume 0.5mm or 0.05 mbar is the resolvable limit in that time, work out
the volume of 22 and 15 mm pipe , Boyle's law etc to deternmine what the
soundness test means in terms of cu ft / hr as an upper bound


The details are in the FAQ.

Resolution is about 0.25mbar i.e less than 0.25mb drop in 2 minutes is a
pass.
Here is the text:

(ii) Check for soundness against leakage
Original text by "The Boilerdoctor" posted to uk.d-i-y on 15/12/1998,
revised 29/1/2002.

This test only applies to a U6 domestic meter; other sizes of meter
require different figures for allowable pressure drop. The gas under test
is Natural Gas. LPG requires a different treatment; longer test periods,
higher test pressures, and no drop at all is permitted. A standard
manometer capable of reading 0 to 12" WG or 0 to 30 mbar, and a length
(approximately 18") of 1/4" rubber hose is required, and also a supply of
leak detect solution.

During the test, DO NOT SMOKE or allow any sources of ignition near.

1. Check that all outlets and appliance taps are off and pilot lights
extinguished. If the installation includes a cooker with a drop down lid
which automatically extinguishes the rings when closed make sure that
this lid is raised but the taps are off - this is to ensure that as far
as possible the cooker internal connections are included in the test.

2. Turn off the gas service valve at the live side of the meter, remove
the test point screw on the discharge branch of the meter and connect the
manometer to the test point using the flexible hose.

Open the gas valve SLOWLY until a reading of approximately 8" WG or 20
mbar is obtained in the system, then close the valve. Allow to stand for
two minutes to stabilise. The pressure should remain close to the initial
pressure, though thermal effects may cause a slight rise or fall. If the
pressure has risen at all, bleed a little off to ensure that the system
pressure is not exceeding 8" WG or 20 mbar. If the pressure is above this
level, a condition known as Governor Lock-Up may have occurred causing a
misleading reading.
Governor lock up occurs when the pressure downstream of the governor is
at or above the set pressure, and hence the governor internal valve is
closed. This traps the high pressure gas upstream and if the supply valve
is then closed a quantity of high pressure gas remains trapped between
the supply valve and the governor. This is a resevoir of high pressure
gas and a small drop downstream of the governor will result in the
governor valve passing some of this gas. A small loss will thus be masked
by this replenishment of the governed side by the high pressure side.
Testing at just below the set pressure means the governor valve will be
open and thus the test is valid all the way back to the supply valve.
3. If this happens, repeat the procedure ensuring the gas valve is opened
very slowly.

4. Take an initial reading of the manometer. Wait two minutes. Take a
final reading of the manometer. Subtract the final reading from the
initial reading and record any loss of pressure.

5. If the system pressure has risen during the test, the most likely
cause is "let by" of the gas valve, in which case the test is invalid and
you must seek help from Transco to repair the fault on the Meter Control
Valve (MCV). If no detectable pressure rise has occurred, bleed off the
pressure until the gauge reads about half of the test pressure. Observe
the pressure again to ensure that the pressure does not rise from this
reduced level. This is to check that the gas valve is not letting a small
amount of gas by, which just might match a loss rate at full test
pressure.

6. If all appliances are still connected to the system, a permissible
pressure loss of 1.6" WG or 4 mbar is allowed provided there is no smell
of gas! If the appliances are isolated from the system under test or, in
other words, the test is on pipework only, then no drop is permitted. If
the above conditions are not satisfied, the leak must be traced and
rectified, and the system re-tested in its entirety. This is because of
the possibility of more than one leak.

7. If the test is satisfactory, remove the gauge, replace the test point
screw, and restore the gas supply. Then test the test point for leakage
with leak detection solution.






--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot light, via the
meter test dial, yesterday, within usual range, as reported on the
internet.
Then today I thought I'd see if there was any leak in the whole system.
Turned off the boiler totally just after breakfast and then took readings
every hour. Reading increased about 0.0001 cu ft in first hour and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just be recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu ft per
hour
leak acceptable, no gas has ever been smelt by anyone. How much influence
from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for manometer
testing is, ie what mm or no mm of water drop over how many minutes at
what
gas pressure, then volume of pipe runs etc to determine it that way. But
neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm
= 354 cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80
means an increase in volume (the leak) of 1/80
so 0.2/80 = 0.0025 cu ft in 2 minutes
= 0.075 cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

N Cook wrote:

Then today I thought I'd see if there was any leak in the whole system.
Turned off the boiler totally just after breakfast and then took readings
every hour. Reading increased about 0.0001 cu ft in first hour and 0.0001 cu
ft in the next 3 hours. Would most of that first hour just be recovering in

I would be wary of using just the meter to make any kind of leak
assessment. The procedure posted by Ed using a manometer (water gauge)
is a far more reliable (and the correct) way to do it.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote in message
...
N Cook wrote:

Then today I thought I'd see if there was any leak in the whole system.
Turned off the boiler totally just after breakfast and then took
readings
every hour. Reading increased about 0.0001 cu ft in first hour and
0.0001 cu
ft in the next 3 hours. Would most of that first hour just be recovering
in

I would be wary of using just the meter to make any kind of leak
assessment. The procedure posted by Ed using a manometer (water gauge)
is a far more reliable (and the correct) way to do it.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/



The other interpretation is that the "soundness test" is a very lax test.
For a pilot light consumption of 0.005 cu ft / hour you could have 15 such
pilot lights all blown out and still not show a leak via the manometer test.
Hopefully you could smell the combination of 15 blown out pilots-worth of
gas though.

On Sat, 08 Mar 2008 16:12:51 +0000, N Cook wrote:

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot light, via
the meter test dial, yesterday, within usual range, as reported on the
internet.
Then today I thought I'd see if there was any leak in the whole system.
Turned off the boiler totally just after breakfast and then took
readings every hour. Reading increased about 0.0001 cu ft in first hour
and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu ft per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for manometer
testing is, ie what mm or no mm of water drop over how many minutes at
what
gas pressure, then volume of pipe runs etc to determine it that way.
But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm = 354
cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase in
volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu ft in 2 minutes = 0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

20mb gauge is about 1020mb absolute.
No redo your calcs.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On Sun, 09 Mar 2008 14:58:19 +0000, N Cook wrote:

John Rumm wrote in message
...
N Cook wrote:

Then today I thought I'd see if there was any leak in the whole
system. Turned off the boiler totally just after breakfast and then
took
readings
every hour. Reading increased about 0.0001 cu ft in first hour and
0.0001 cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in

I would be wary of using just the meter to make any kind of leak
assessment. The procedure posted by Ed using a manometer (water gauge)
is a far more reliable (and the correct) way to do it.


--
Cheers,

John.

/================================================== ===============\ |
Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------| |
John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/



The other interpretation is that the "soundness test" is a very lax
test. For a pilot light consumption of 0.005 cu ft / hour you could have
15 such pilot lights all blown out and still not show a leak via the
manometer test. Hopefully you could smell the combination of 15 blown
out pilots-worth of gas though.

Anyone who has done the test knows that a pilot light will produce
a descending gauge that drops in seconds.
Your calcs confused gauge with absolute pressures.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Ed Sirett wrote in message
...
On Sat, 08 Mar 2008 16:12:51 +0000, N Cook wrote:

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot light, via
the meter test dial, yesterday, within usual range, as reported on the
internet.
Then today I thought I'd see if there was any leak in the whole system.
Turned off the boiler totally just after breakfast and then took
readings every hour. Reading increased about 0.0001 cu ft in first hour
and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu ft per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for manometer
testing is, ie what mm or no mm of water drop over how many minutes at
what
gas pressure, then volume of pipe runs etc to determine it that way.
But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm = 354
cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase in
volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu ft in 2 minutes = 0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

20mb gauge is about 1020mb absolute.
No redo your calcs.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html


Interesting point but surely making the pressure in the pipe 1020 mBar and
the air outside at 1000 mBar makes no difference to the calculation

N Cook wrote in message
...
Ed Sirett wrote in message
...
On Sat, 08 Mar 2008 16:12:51 +0000, N Cook wrote:

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot light, via
the meter test dial, yesterday, within usual range, as reported on
the
internet.
Then today I thought I'd see if there was any leak in the whole
system.
Turned off the boiler totally just after breakfast and then took
readings every hour. Reading increased about 0.0001 cu ft in first
hour
and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu ft
per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for
manometer
testing is, ie what mm or no mm of water drop over how many minutes
at
what
gas pressure, then volume of pipe runs etc to determine it that way.
But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm = 354
cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase in
volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu ft in 2 minutes =
0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

20mb gauge is about 1020mb absolute.
No redo your calcs.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html


Interesting point but surely making the pressure in the pipe 1020 mBar and
the air outside at 1000 mBar makes no difference to the calculation



surely the calculation is the same as considering an absolute pressure of
20mB in the pipe and a vacuum outside.

On Mon, 10 Mar 2008 09:40:07 +0000, N Cook wrote:

N Cook wrote in message
...
Ed Sirett wrote in message
...
On Sat, 08 Mar 2008 16:12:51 +0000, N Cook wrote:

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot light,
via the meter test dial, yesterday, within usual range, as
reported on
the
internet.
Then today I thought I'd see if there was any leak in the whole
system.
Turned off the boiler totally just after breakfast and then took
readings every hour. Reading increased about 0.0001 cu ft in first
hour
and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu ft
per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for
manometer
testing is, ie what mm or no mm of water drop over how many
minutes
at
what
gas pressure, then volume of pipe runs etc to determine it that
way. But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm =
354 cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase
in volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu ft in 2 minutes
=
0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

20mb gauge is about 1020mb absolute.
No redo your calcs.


--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ
for uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler FAQ
http://www.makewrite.demon.co.uk/BoilerChoice.html


Interesting point but surely making the pressure in the pipe 1020 mBar
and the air outside at 1000 mBar makes no difference to the calculation



surely the calculation is the same as considering an absolute pressure
of 20mB in the pipe and a vacuum outside.

Quite correct the calculation is independent of the external pressure.
It is not however independent of the absolute pressure of the gas in the
pipe.

The mistake you made was the bit where you applied Boyle's law to the
gauge pressure of the gas in the pipe.

So 0.25mb is a change of 0.25/1020 (or thereabouts) not a change of
0.25/20 which is about 1/4000 no 1/80 which reduces the maximum leakage
rate by a factor of about 50. Although you've also neglected to take the
very substantial volume of the gas meter into account.

Anyway the acceptable limits for normal domestic natural gas + U6 meter
installations a
Pipework max 0.25mbar (difference in gauge pressure) in 2 minutes.
Or max 4 mbar difference in gauge pressure in 2 minutes provided all of
* Existing installation.
* Appliances connected.
* No small of gas reported by user.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Ed Sirett wrote in message
...
On Mon, 10 Mar 2008 09:40:07 +0000, N Cook wrote:

N Cook wrote in message
...
Ed Sirett wrote in message
...
On Sat, 08 Mar 2008 16:12:51 +0000, N Cook wrote:

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot light,
via the meter test dial, yesterday, within usual range, as
reported on
the
internet.
Then today I thought I'd see if there was any leak in the whole
system.
Turned off the boiler totally just after breakfast and then took
readings every hour. Reading increased about 0.0001 cu ft in first
hour
and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu ft
per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for
manometer
testing is, ie what mm or no mm of water drop over how many
minutes
at
what
gas pressure, then volume of pipe runs etc to determine it that
way. But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm =
354 cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase
in volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu ft in 2 minutes
=
0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

20mb gauge is about 1020mb absolute.
No redo your calcs.


--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ
for uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler FAQ
http://www.makewrite.demon.co.uk/BoilerChoice.html


Interesting point but surely making the pressure in the pipe 1020 mBar
and the air outside at 1000 mBar makes no difference to the calculation



surely the calculation is the same as considering an absolute pressure
of 20mB in the pipe and a vacuum outside.

Quite correct the calculation is independent of the external pressure.
It is not however independent of the absolute pressure of the gas in the
pipe.

The mistake you made was the bit where you applied Boyle's law to the
gauge pressure of the gas in the pipe.

So 0.25mb is a change of 0.25/1020 (or thereabouts) not a change of
0.25/20 which is about 1/4000 no 1/80 which reduces the maximum leakage
rate by a factor of about 50. Although you've also neglected to take the
very substantial volume of the gas meter into account.

Anyway the acceptable limits for normal domestic natural gas + U6 meter
installations a
Pipework max 0.25mbar (difference in gauge pressure) in 2 minutes.
Or max 4 mbar difference in gauge pressure in 2 minutes provided all of
* Existing installation.
* Appliances connected.
* No small of gas reported by user.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html


I'm still not convinced.
Would the rate of loss of gas from the 1020mB situation to 1000mB outside be
any different to 20mB absolute in the pipe escaping to a vacuum through the
same hole?
Yess I'd not thought of the volume in the meter, I assume that is on the
consumer side of the vane or whatever momnitors the throughput.

On Mon, 10 Mar 2008 13:24:45 +0000, N Cook wrote:

Ed Sirett wrote in message
...
On Mon, 10 Mar 2008 09:40:07 +0000, N Cook wrote:

N Cook wrote in message
...
Ed Sirett wrote in message
...
On Sat, 08 Mar 2008 16:12:51 +0000, N Cook wrote:

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot
light, via the meter test dial, yesterday, within usual range,
as reported on
the
internet.
Then today I thought I'd see if there was any leak in the whole
system.
Turned off the boiler totally just after breakfast and then
took readings every hour. Reading increased about 0.0001 cu ft
in first
hour
and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu
ft
per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for
manometer
testing is, ie what mm or no mm of water drop over how many
minutes
at
what
gas pressure, then volume of pipe runs etc to determine it that
way. But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm
= 354 cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an
increase in volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu ft
in 2 minutes =
0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

20mb gauge is about 1020mb absolute.
No redo your calcs.


--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ
for uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler
FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html


Interesting point but surely making the pressure in the pipe 1020
mBar and the air outside at 1000 mBar makes no difference to the
calculation



surely the calculation is the same as considering an absolute
pressure of 20mB in the pipe and a vacuum outside.

Quite correct the calculation is independent of the external pressure.
It is not however independent of the absolute pressure of the gas in
the pipe.

The mistake you made was the bit where you applied Boyle's law to the
gauge pressure of the gas in the pipe.

So 0.25mb is a change of 0.25/1020 (or thereabouts) not a change of
0.25/20 which is about 1/4000 no 1/80 which reduces the maximum leakage
rate by a factor of about 50. Although you've also neglected to take
the very substantial volume of the gas meter into account.

Anyway the acceptable limits for normal domestic natural gas + U6 meter
installations a
Pipework max 0.25mbar (difference in gauge pressure) in 2 minutes. Or
max 4 mbar difference in gauge pressure in 2 minutes provided all of
* Existing installation.
* Appliances connected.
* No small of gas reported by user.


--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ for
uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler FAQ
http://www.makewrite.demon.co.uk/BoilerChoice.html


I'm still not convinced.
Would the rate of loss of gas from the 1020mB situation to 1000mB
outside be any different to 20mB absolute in the pipe escaping to a
vacuum through the same hole?
Yess I'd not thought of the volume in the meter, I assume that is on the
consumer side of the vane or whatever momnitors the throughput.

I have gone back to your original post. One rev of the pointer on a meter
with a pointer is 1 cubic ft. I don't see how you managed to measure
0.0001 cu. ft. or whatever.

Anyway the exact chapter and verse for gas tightness testing is given in
IGE/UP/1B which is a snip at a mere £77

A summary of this is widely known and reproduced in most gas fitting as
stated above.

we are concerned that the amount of gas leakage at about atmospheric
pressure is below a small amount. A loss of less than 0.25mb in about
1000mbar in 2mins is 1/8000 the volume of the installation per minute.

A typical domestic installation including the meter might be about 8
litres of gas. So we are looking to leak less than 1 cubic cm. of gas per
minute.

If you are not smelling gas you need do nothing.
If you think you have a leak then if you have the equipment and skills
perform a tightness test in line with the method stated, or call for pro
help.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Ed Sirett wrote in message
...
On Mon, 10 Mar 2008 13:24:45 +0000, N Cook wrote:

Ed Sirett wrote in message
...
On Mon, 10 Mar 2008 09:40:07 +0000, N Cook wrote:

N Cook wrote in message
...
Ed Sirett wrote in message
...
On Sat, 08 Mar 2008 16:12:51 +0000, N Cook wrote:

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot
light, via the meter test dial, yesterday, within usual range,
as reported on
the
internet.
Then today I thought I'd see if there was any leak in the whole
system.
Turned off the boiler totally just after breakfast and then
took readings every hour. Reading increased about 0.0001 cu ft
in first
hour
and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu
ft
per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for
manometer
testing is, ie what mm or no mm of water drop over how many
minutes
at
what
gas pressure, then volume of pipe runs etc to determine it that
way. But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm
= 354 cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an
increase in volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu ft
in 2 minutes =
0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

20mb gauge is about 1020mb absolute.
No redo your calcs.


--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ
for uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler
FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html


Interesting point but surely making the pressure in the pipe 1020
mBar and the air outside at 1000 mBar makes no difference to the
calculation



surely the calculation is the same as considering an absolute
pressure of 20mB in the pipe and a vacuum outside.

Quite correct the calculation is independent of the external pressure.
It is not however independent of the absolute pressure of the gas in
the pipe.

The mistake you made was the bit where you applied Boyle's law to the
gauge pressure of the gas in the pipe.

So 0.25mb is a change of 0.25/1020 (or thereabouts) not a change of
0.25/20 which is about 1/4000 no 1/80 which reduces the maximum leakage
rate by a factor of about 50. Although you've also neglected to take
the very substantial volume of the gas meter into account.

Anyway the acceptable limits for normal domestic natural gas + U6 meter
installations a
Pipework max 0.25mbar (difference in gauge pressure) in 2 minutes. Or
max 4 mbar difference in gauge pressure in 2 minutes provided all of
* Existing installation.
* Appliances connected.
* No small of gas reported by user.


--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ for
uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler FAQ
http://www.makewrite.demon.co.uk/BoilerChoice.html


I'm still not convinced.
Would the rate of loss of gas from the 1020mB situation to 1000mB
outside be any different to 20mB absolute in the pipe escaping to a
vacuum through the same hole?
Yess I'd not thought of the volume in the meter, I assume that is on the
consumer side of the vane or whatever momnitors the throughput.

I have gone back to your original post. One rev of the pointer on a meter
with a pointer is 1 cubic ft. I don't see how you managed to measure
0.0001 cu. ft. or whatever.

Anyway the exact chapter and verse for gas tightness testing is given in
IGE/UP/1B which is a snip at a mere £77

A summary of this is widely known and reproduced in most gas fitting as
stated above.

we are concerned that the amount of gas leakage at about atmospheric
pressure is below a small amount. A loss of less than 0.25mb in about
1000mbar in 2mins is 1/8000 the volume of the installation per minute.

A typical domestic installation including the meter might be about 8
litres of gas. So we are looking to leak less than 1 cubic cm. of gas per
minute.

If you are not smelling gas you need do nothing.
If you think you have a leak then if you have the equipment and skills
perform a tightness test in line with the method stated, or call for pro
help.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html



there are 4 black and white digits that go on the gas bill as "units" then 2
red digits with cu ft written under this "milometer" section and then a dial
scaled 0 to 1.
So the red ones are not 1/10 and 1/100 of a cu ft leaving the last one as
1/100 of a cu ft for one rev which you can read to 1/10000 ?

On 10/03/2008 22:21, N Cook wrote:

there are 4 black and white digits that go on the gas bill as "units"

Usually HUNDRED cubic feet?

Andy Burns wrote in message
...
On 10/03/2008 22:21, N Cook wrote:

there are 4 black and white digits that go on the gas bill as "units"

Usually HUNDRED cubic feet?


As the last watch dial pointer one is marked 0 to 1 , would int not the 4
charged numbers be thousands to 1 "gas unit" ?

N Cook wrote in message
...
N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot light, via
the
meter test dial, yesterday, within usual range, as reported on the
internet.
Then today I thought I'd see if there was any leak in the whole system.
Turned off the boiler totally just after breakfast and then took
readings
every hour. Reading increased about 0.0001 cu ft in first hour and
0.0001
cu
ft in the next 3 hours. Would most of that first hour just be recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu ft per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence
from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for manometer
testing is, ie what mm or no mm of water drop over how many minutes at
what
gas pressure, then volume of pipe runs etc to determine it that way. But
neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm
= 354 cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80
means an increase in volume (the leak) of 1/80
so 0.2/80 = 0.0025 cu ft in 2 minutes
= 0.075 cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr



I'll get there in the end.
I dug out a gas bill and although it doesn't say what a gas unit is.
It uses a conversion factor of 2.83 which is the conversion of 100s of cu ft
to cu m.
So I'm out in the above by a factor of 100.
1 gas unit = 100 cubic feet
Still don't know what internal gas meter vol is
but manometer test discrimination is 7.5 cu ft per hour
and the "leak" I measured on the watch dial pointer means something like
0.01 to 0.003 cu ft per hour.

I will repeat the calc some time by assuming the complete exterior vol of
the gas meter is the vol to be included with the pipe run as I cannot find
what that vol is

On Mon, 10 Mar 2008 22:21:04 +0000, N Cook wrote:

Ed Sirett wrote in message
...
On Mon, 10 Mar 2008 13:24:45 +0000, N Cook wrote:

Ed Sirett wrote in message
...
On Mon, 10 Mar 2008 09:40:07 +0000, N Cook wrote:

N Cook wrote in message
...
Ed Sirett wrote in message
...
On Sat, 08 Mar 2008 16:12:51 +0000, N Cook wrote:

N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot
light, via the meter test dial, yesterday, within usual
range, as reported on
the
internet.
Then today I thought I'd see if there was any leak in the
whole
system.
Turned off the boiler totally just after breakfast and then
took readings every hour. Reading increased about 0.0001 cu
ft in first
hour
and 0.0001
cu
ft in the next 3 hours. Would most of that first hour just
be recovering
in
pressure over the whole gas distribution system ? Is 0.00003
cu ft
per
hour
leak acceptable, no gas has ever been smelt by anyone. How
much influence from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria
for
manometer
testing is, ie what mm or no mm of water drop over how many
minutes
at
what
gas pressure, then volume of pipe runs etc to determine it
that way. But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu
mm = 354 cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an
increase in volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu
ft in 2 minutes =
0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr

20mb gauge is about 1020mb absolute.
No redo your calcs.


--
Ed Sirett - Property maintainer and registered gas fitter. The
FAQ for uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a
Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html


Interesting point but surely making the pressure in the pipe 1020
mBar and the air outside at 1000 mBar makes no difference to the
calculation



surely the calculation is the same as considering an absolute
pressure of 20mB in the pipe and a vacuum outside.

Quite correct the calculation is independent of the external
pressure. It is not however independent of the absolute pressure of
the gas in the pipe.

The mistake you made was the bit where you applied Boyle's law to
the gauge pressure of the gas in the pipe.

So 0.25mb is a change of 0.25/1020 (or thereabouts) not a change of
0.25/20 which is about 1/4000 no 1/80 which reduces the maximum
leakage rate by a factor of about 50. Although you've also neglected
to take the very substantial volume of the gas meter into account.

Anyway the acceptable limits for normal domestic natural gas + U6
meter installations a
Pipework max 0.25mbar (difference in gauge pressure) in 2 minutes.
Or max 4 mbar difference in gauge pressure in 2 minutes provided all
of
* Existing installation.
* Appliances connected.
* No small of gas reported by user.


--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ
for uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler FAQ
http://www.makewrite.demon.co.uk/BoilerChoice.html


I'm still not convinced.
Would the rate of loss of gas from the 1020mB situation to 1000mB
outside be any different to 20mB absolute in the pipe escaping to a
vacuum through the same hole?
Yess I'd not thought of the volume in the meter, I assume that is on
the consumer side of the vane or whatever momnitors the throughput.

I have gone back to your original post. One rev of the pointer on a
meter with a pointer is 1 cubic ft. I don't see how you managed to
measure 0.0001 cu. ft. or whatever.

Anyway the exact chapter and verse for gas tightness testing is given
in IGE/UP/1B which is a snip at a mere £77

A summary of this is widely known and reproduced in most gas fitting as
stated above.

we are concerned that the amount of gas leakage at about atmospheric
pressure is below a small amount. A loss of less than 0.25mb in about
1000mbar in 2mins is 1/8000 the volume of the installation per
minute.

A typical domestic installation including the meter might be about 8
litres of gas. So we are looking to leak less than 1 cubic cm. of gas
per minute.

If you are not smelling gas you need do nothing. If you think you have
a leak then if you have the equipment and skills perform a tightness
test in line with the method stated, or call for pro help.

--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ for
uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler FAQ
http://www.makewrite.demon.co.uk/BoilerChoice.html



there are 4 black and white digits that go on the gas bill as "units"
then 2 red digits with cu ft written under this "milometer" section and
then a dial scaled 0 to 1.
So the red ones are not 1/10 and 1/100 of a cu ft leaving the last one
as 1/100 of a cu ft for one rev which you can read to 1/10000 ?

Assuming this is normal domestic gas meter the black didits are m^3
IIRC
The red ones are 0.1 m^3 and 0.01 m^3 (i.e about 3.5 and 0.35 cu ft.)

The dial reads 1 cu ft per rev. Due to the way the meter works the
dial is not linear with respect to volumes smaller than 1 rev.

1 rpm of the dial is 18kw


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On Tue, 11 Mar 2008 10:24:17 +0000, N Cook wrote:

N Cook wrote in message
...
N Cook wrote in message
...
Decided to measure the gas consumption of the boiler pilot light, via
the
meter test dial, yesterday, within usual range, as reported on the
internet.
Then today I thought I'd see if there was any leak in the whole
system. Turned off the boiler totally just after breakfast and then
took
readings
every hour. Reading increased about 0.0001 cu ft in first hour and
0.0001
cu
ft in the next 3 hours. Would most of that first hour just be
recovering
in
pressure over the whole gas distribution system ? Is 0.00003 cu ft
per
hour
leak acceptable, no gas has ever been smelt by anyone. How much
influence
from changes in atmospheric pressure ?

I tried googling for that info and also what the criteria for
manometer testing is, ie what mm or no mm of water drop over how many
minutes at
what
gas pressure, then volume of pipe runs etc to determine it that way.
But neither found.




My calculation, not checked by anyone else yet,
for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm = 354
cu ins
= 0.2 cu ft

By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase in
volume (the leak) of 1/80 so 0.2/80 = 0.0025 cu ft in 2 minutes = 0.075
cu ft per hour
well above 0.0001 cu ft / hour let alone 0.00003 cu ft per hr



I'll get there in the end.
I dug out a gas bill and although it doesn't say what a gas unit is. It
uses a conversion factor of 2.83 which is the conversion of 100s of cu
ft to cu m.
So I'm out in the above by a factor of 100. 1 gas unit = 100 cubic feet
Still don't know what internal gas meter vol is but manometer test
discrimination is 7.5 cu ft per hour and the "leak" I measured on the
watch dial pointer means something like 0.01 to 0.003 cu ft per hour.

I will repeat the calc some time by assuming the complete exterior vol
of the gas meter is the vol to be included with the pipe run as I cannot
find what that vol is

Sorry you have quite an old gas meter which has black digits reading in
00s of cu ft.

Anyway the dial is still 1 cu.ft. per rev.

Any cryptic comments like 0.071 cu .ft /rev refer to the internal
mechanism of the meter not the testing dial.


--


Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Return to original calculation

for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm
= 354 cu ins
= 0.2 cu ft
Volume of whole gas meter = 5x7x8 inches
=.16 cu ft

Therefore maximum vol = .36 cu ft


By Boyle's law drop in pressure of 0.25/20 = 1/80
means an increase in volume (the leak) of 1/80
so 0.36/80 = 0.0045 cu ft in 2 minutes
= 0.135 cu ft per hour
well above 0.01 cu ft / hour let alone 0.003 cu ft per hr
read on the watch dial pointer of the meter

Pilot light consumption about 0.5 cu ft / hour so 3 times the minimum
resolvable amount in the soundness test. So manometer test determines a leak
of gas of degree 1/3 of a pilot light or more. I'll settle for that unless
anyone knows the consumer side volume of a gas meter .

On Tue, 11 Mar 2008 16:05:45 +0000, N Cook wrote:

Return to original calculation

for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm = 354
cu ins
= 0.2 cu ft
Volume of whole gas meter = 5x7x8 inches =.16 cu ft

Therefore maximum vol = .36 cu ft

So far so good.


By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase in
volume (the leak) of 1/80 so 0.36/80 = 0.0045 cu ft in 2 minutes = 0.135
cu ft per hour

No! No! No! it is 0.25mb change in an absolute pressure of atmospheric+20
say 1000+20 (varying on the weather by several percent +/-).

Boyles law applies to absolute pressures not gauge pressure.

Example a bicycle pump (in perfect working order) starts with the handle
out and the pressure inside the pump at 0 bar gauge (as shown by the
pressure gauge it is connected to), the absolute pressure is 1 bar. You
move the handle in half way the pressure rises to 2 bar absolute (Boyles
law) and 1 bar on the gauge.

The gas companies make a slight adjustment to the gas bill dependent on
the average weather to allow for the fact that they supply slightly more
gas in times of high atmospheric pressure or vice versa.

It is because the pressure decay method is showing the difference between
the absolute pressures that small changes in the guage pressure
correspond to very very small leaks.

The method is so sensitive that simply placing your hand on the gas pipe
for 15 seconds can make the gauge move up a small amount (say 0.25 mbar).
Try it! (or removing the meter box cover in direct sunlight).

By a similar calculation....

Temp rise of 200mm of pipe from 17 to 37C (290K to 310K). Fraction of
total volume of warmed pipe 1/200 (say 20m of pipe + same volume in gas
meter). Fractional pressure rise (Ideal gas law), for warmed section is
about 20K/300K i.e. 1/15. The product or the fractions is the rise in
absolute pressure of 1 part in 3000 (15*200). I.e. about 1/3 of a mbar.

I have given this my best shot of trying to convince you the pressure
decay method is sensitive and effective. Watching the dial is NOT the way
to test for leaks.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Ed Sirett wrote in message
...
On Tue, 11 Mar 2008 16:05:45 +0000, N Cook wrote:

Return to original calculation

for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm = 354
cu ins
= 0.2 cu ft
Volume of whole gas meter = 5x7x8 inches =.16 cu ft

Therefore maximum vol = .36 cu ft

So far so good.


By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase in
volume (the leak) of 1/80 so 0.36/80 = 0.0045 cu ft in 2 minutes = 0.135
cu ft per hour

No! No! No! it is 0.25mb change in an absolute pressure of atmospheric+20
say 1000+20 (varying on the weather by several percent +/-).

Boyles law applies to absolute pressures not gauge pressure.

Example a bicycle pump (in perfect working order) starts with the handle
out and the pressure inside the pump at 0 bar gauge (as shown by the
pressure gauge it is connected to), the absolute pressure is 1 bar. You
move the handle in half way the pressure rises to 2 bar absolute (Boyles
law) and 1 bar on the gauge.

The gas companies make a slight adjustment to the gas bill dependent on
the average weather to allow for the fact that they supply slightly more
gas in times of high atmospheric pressure or vice versa.

It is because the pressure decay method is showing the difference between
the absolute pressures that small changes in the guage pressure
correspond to very very small leaks.

The method is so sensitive that simply placing your hand on the gas pipe
for 15 seconds can make the gauge move up a small amount (say 0.25 mbar).
Try it! (or removing the meter box cover in direct sunlight).

By a similar calculation....

Temp rise of 200mm of pipe from 17 to 37C (290K to 310K). Fraction of
total volume of warmed pipe 1/200 (say 20m of pipe + same volume in gas
meter). Fractional pressure rise (Ideal gas law), for warmed section is
about 20K/300K i.e. 1/15. The product or the fractions is the rise in
absolute pressure of 1 part in 3000 (15*200). I.e. about 1/3 of a mbar.

I have given this my best shot of trying to convince you the pressure
decay method is sensitive and effective. Watching the dial is NOT the way
to test for leaks.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html


Are you sure 0.25mB is the resolution of a manometer as that is 2.5 mm of
water, I would have thought .5mm or .05 mB was the resolvable movement?

Swapping manometer for Borden gauge as the water would boil.

What is your calculation for the following situations?

Volume of pipe V, at absolute pressure 1020mB leaking to air at 1000mB
pressure
and same pipe but at absolute pressure 20mB leaking to a vacuum ?

Same leak rate or different?

On Wed, 12 Mar 2008 08:04:25 +0000, N Cook wrote:

Ed Sirett wrote in message
...
On Tue, 11 Mar 2008 16:05:45 +0000, N Cook wrote:

Return to original calculation

for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm =
354 cu ins
= 0.2 cu ft
Volume of whole gas meter = 5x7x8 inches =.16 cu ft

Therefore maximum vol = .36 cu ft

So far so good.


By Boyle's law drop in pressure of 0.25/20 = 1/80 means an increase
in volume (the leak) of 1/80 so 0.36/80 = 0.0045 cu ft in 2 minutes =
0.135 cu ft per hour

No! No! No! it is 0.25mb change in an absolute pressure of
atmospheric+20 say 1000+20 (varying on the weather by several percent
+/-).

Boyles law applies to absolute pressures not gauge pressure.

Example a bicycle pump (in perfect working order) starts with the
handle out and the pressure inside the pump at 0 bar gauge (as shown by
the pressure gauge it is connected to), the absolute pressure is 1 bar.
You move the handle in half way the pressure rises to 2 bar absolute
(Boyles law) and 1 bar on the gauge.

The gas companies make a slight adjustment to the gas bill dependent on
the average weather to allow for the fact that they supply slightly
more gas in times of high atmospheric pressure or vice versa.

It is because the pressure decay method is showing the difference
between the absolute pressures that small changes in the guage pressure
correspond to very very small leaks.

The method is so sensitive that simply placing your hand on the gas
pipe for 15 seconds can make the gauge move up a small amount (say 0.25
mbar). Try it! (or removing the meter box cover in direct sunlight).

By a similar calculation....

Temp rise of 200mm of pipe from 17 to 37C (290K to 310K). Fraction of
total volume of warmed pipe 1/200 (say 20m of pipe + same volume in
gas meter). Fractional pressure rise (Ideal gas law), for warmed
section is about 20K/300K i.e. 1/15. The product or the fractions is
the rise in absolute pressure of 1 part in 3000 (15*200). I.e. about
1/3 of a mbar.

I have given this my best shot of trying to convince you the pressure
decay method is sensitive and effective. Watching the dial is NOT the
way to test for leaks.



--
Ed Sirett - Property maintainer and registered gas fitter. The FAQ for
uk.diy is at http://www.diyfaq.org.uk Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html Choosing a Boiler FAQ
http://www.makewrite.demon.co.uk/BoilerChoice.html


Are you sure 0.25mB is the resolution of a manometer as that is 2.5 mm
of water, I would have thought .5mm or .05 mB was the resolvable
movement?

It's 2.5mm of /difference/ so the water level only moves half that on one
side of the gauge.

Given the meniscus and parallax errors of observation a 1mm movement is a
practical minimum detectable movement, although you could probably do a
bit better.

The 0.25mbar allowance was introduced because the electronic manometers
are so sensitive that the last digit (0.01 mbar) never settles.



Swapping manometer for Borden gauge as the water would boil.

What is your calculation for the following situations?

Volume of pipe V, at absolute pressure 1020mB leaking to air at 1000mB
pressure
and same pipe but at absolute pressure 20mB leaking to a vacuum ?

Same leak rate or different?

The same leakage rate. But the there's 50x less gas in the pipe and the
percentage drop in absolute pressure is 50x greater.


Taking 120mbar against 100mbar the same leakage rate but 10x less gas in
pipe.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Ed Sirett wrote in message
...
On Wed, 12 Mar 2008 08:04:25 +0000, N Cook wrote:

Ed Sirett wrote in message
...
On Tue, 11 Mar 2008 16:05:45 +0000, N Cook wrote:

Return to original calculation



The same leakage rate. But the there's 50x less gas in the pipe and the
percentage drop in absolute pressure is 50x greater.


Taking 120mbar against 100mbar the same leakage rate but 10x less gas in
pipe.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html


Ah the penny has dropped, same rate but convert the vacuum case to standard
temp and pressure and there is a factor of 50 to take into account

Return to original calculation, hopefully last time

for 0.25 mBar reduction in 20mB over 2 minutes

11m of 22mm pipe and 9m of 15mm pipe, no known dead runs.

volume of that pipe between meter and appliances 5,800,000 cu mm
= 354 cu ins
= 0.2 cu ft
Volume of whole gas meter = 5x7x8 inches
=.16 cu ft

Therefore maximum vol = .36 cu ft


By Boyle's law drop in pressure of 0.25/1020 = 0.000245
means an increase in volume (the leak) of that factor
so 0.36/(1/0.000245) = 0.000088 cu ft in 2 minutes
= 0.0026 cu ft per hour

Pilot light consumption about 0.5 cu ft / hour so about 200 times the
minimum resolvable amount in the soundness test.