gas pressure and height

[ambrosia]

spent the day checking working pressures on boilers in a block of flats, we were checking existing pipe sizing before replacing all the boilers

i was doing the working pressure at the boiler, while my colleague (who is incidentally a blithering idiot), was at the meter monitoring the pressure

The flats were up to 8 floors above the meters and i on the top floor was measuring up to 2mbar higher than my colleague below

I very vaguely remember something in collage about 'because gas rises the pressure can be higher at the top of a vertical pipe run,' is this true and is there a formula for working it out

or am i simply imagining this as i seek a reason for the difference we recorded

 

[jtsplumbing]

Just seen a pice about this in the PHM mag, yes you are right the pres will be higher what it say's is it will increse by 0.0492 mbar for every 1 Mtr of pipe rise, the same will happen for every 1 Mtr drop the pres will fall by 0.0492 mbar hope this helps

 

[diamondgas]

Interesting question ambrosia

I know atmospheric pressure will reduce the higher you go up maybe that has the effect you describe as it plays a big part in how pressure is measured

 

[mountainman]

Sounds plausible!
Never encountered this myself though even during tests in tower blocks.
Perhaps Boyles Law has some relevance!!

 

[ambrosia]

it will increse by 0.0492 mbar for every 1 Mtr of pipe rise

now thats why I love this forum, I could have spent ages researching that question, the whole time doubting myself and wondering if i had made it up

Many thanks JTS

 

[SafeGasInstall]

are you saying flat on floor 8 had its own gas meter on the ground ?

 

[zzzjim]

A bit of both , NG lighter than air , and air pressure drops with height !

 

[diamondgas]

are you saying flat on floor 8 had its own gas meter on the ground ?

Seen blocks with rows of outside sunken meter's SGI The flats have secondary ECV's ... I wonder how many test the pipe between the meter and secondary ecv? hmmm

 

[ambrosia]

are you saying flat on floor 8 had its own gas meter on the ground ?

all the flats had meters at street level

Seen blocks with rows of outside sunken meter's SGI

The flats have secondary ECV's ... I wonder how many test the pipe between the meter and secondary ecv? hmmm

must admit i didnt, passed a tightness test so i left it, have i missed a reg

youve got me thinking now, with that long a 28mm pipe run i should have calculated the volume, could have been bordering on commercial

 

[SafeGasInstall]

Must have been more then 21m

 

[diamondgas]

all the flats had meters at street level



must admit i didnt, passed a tightness test so i left it, have i missed a reg

One for Kirkgas I think ambrosia ... I have one on contract fro a landlord and I tested at the meter. What a balls ache up and down. It was only 2 stories up!

 

[Pssst]

Gas pressure as measured on your water guage is simply guage pressure.

Absolute pressure is atmospheric pressure + guage pressure.

If you visualise your guage, one side is connected to the gas supply and measures its pressure. The other leg of your guage is connected to atmospheric pressure.

As the static height of air is less the higher you go up,the gas pressure will appear to rise with respect to atmospheric. Reaaly, it isnt the gas pressure thats rising,its the atmospheric pressure which is reducing.

To be totally accurate,pressures should really be quoted as ABS=Absolute but for simple day to day low pressure work,it really doesnt matter too much.

If you think about your modern motor car with fuel injection systems, it will likely have some measurement/correction mechanism to adjust the fuel air mixture in accordance with extremes of height since otherwise,your car would tend to run over rich at higher altitudes.

 

[SafeGasInstall]

so out of what pssst say if test done with analyser will have no the difference of 2mbar ????

 

[Roger Welton]

are you saying flat on floor 8 had its own gas meter on the ground ?

#

Must be fun gas rating the boilers on your own as well :banghead:

 

[Pssst]

it depends whether the tester gives readings in guage pressure or absolute. Or bring a barometer with you !

 

[kirkgas]

One for Kirkgas I think ambrosia ... I have one on contract fro a landlord and I tested at the meter. What a balls ache up and down. It was only 2 stories up!

off the top of my head at this late hour while i watch man city winning the league, (thats 3 excuses in case im wrong!!!!!!!!!)
max volume of 0.035m3 minus E6 meter volume leaves you about 60m ish of 28mm pipe before you get to commercial (90m ish of 22mm i think) more of an issue with this kind of pipe length is the gas flow by the time it gets to the endd of the pipe

 

[lambchop]

psst & jts superb answers, my missus cant understand why I'm into this forum (redtube is no longer on my favourites), I take my hard hat off to you gentleman.

 

[tom609]

barometer is on the list for next christmas lol interesting post