# Gas pipe sizing

#### Agile

First I must appologise because I replied having read a very basic question and jumping to the conclusion that it could not be an RGI.

I also inadvertently said some might have to be in 32 mm when that is not a standard UK copper tube size.

So to try to answer the probable original question with a more general answer!

You work out all the equivalent lengths after taking elbows and "T" outlets to 90 degree branches ( !!! ) into account.

You then assume for the calculation that all appliances are on and taking their maximum rated power input.

You do the calculation for each section and note the pressure drop for each section. The last section of "about 20 m" comes after the first section and say the drop in the first section is 0.4 mB then the last section can only drop 0.6 mB.

Thats my understanding of the way the calculation is aproached and using those figures then part of the pipe would have to be greater than 28 mm.

Tony

#### chr15

Thanks for the reply mr agile-do you know if its correct what somebody earlier said that a 2mb drop is now allowed between meter and appliances,and I still cant see it needing greater than 28mm although I know you can't comment not knowing full details of the installation.

#### bster

I work it out by like this ..........

pressure loss is calculated (assuming a 1mb permissable drop) by dividing 1 (mb) by the number of sections to the appliance, in this case lets assume 2, that means that 1divided by 2= .5 This figure is then X by the length of that section (say 20m) this = 0.5 x 20 = 10 which is then added to the original 20meters = 30meters (not including fittings\bends)

#### Agile

I would warn everyone who has read this report of 2 mB pressure drop being permissible to treat this as NOT TRUE until it has been independently confirmed.

It seems VERY IRRESPONSIBLE of any anonymous person to make any statement like this without stating a trustworthy and independent source of the information. There is nothing on the CORGI website about it, in fact its all about model cars! Nothing on ARGI either I expect.

Suppose a drunk on a park bench told you all 30 MPH limits were now raised to 40 MPH. Do you think you would get very far in Court by quoting him?

I expect 28 mm may well be adequate but it all depends on the bends near the meter. I cannot work out pressure losses exactly in my head either!

Tony

#### chr15

Agile said:
I expect 28 mm may well be adequate but it all depends on the bends near the meter. I cannot work out pressure losses exactly in my head either!

Tony
Nice to hear it.

#### Bigburn

chr15 said:
So everyone doesn't know everything.

Everyone DO know everything . Its just the individual who dont know everything.

#### chr15

Bigburn said:
chr15 said:
So everyone doesn't know everything.

Everyone DO know everything . Its just the individual who dont know everything.
OK every person doesn't know everything....jeeeez

#### Agile

But whats more worrying is that many people do not know what they do not know!

#### ChrisR

Chr15 I can only assume you don't do much installation and have forgotten what you must have known how to do once, at least..?!
If you find the tables hard try this:
http://www.slumberlands.freeserve.co.uk/gasflow.htm

but take both with a heavy pinch of salt. The actual drops are much higher than the predicted ones.

#### doitall

The one thing that ACS teaches you is to refer to the course books, and where to find the information.

Either you have the reference books from the course or you are not an RGI.

And in any case, anyone with half a brain would see the answer its so obvious.

#### fitz1

mate of mine renewed his ACS last week. 2mb drop now.

#### baxpoti

fitz1 said:
you are now alowed 2 mb drop instead of 1 mb
Has this changed in the last few months and very few people have been informed.????????? I don't think so!

I think you probably meant, you are allowed +/- 2mb at the meter
e.g. a working pressure of 19 - 23mb

1mb is still the figure for pressure drop between the outlet of the meter and the appliance inlet test point. unless M.I. state different.

#### fitz1

you may be right on that. ill do a check and get back. sorry for my hesitance.

#### chr15

ChrisR said:
Chr15 I can only assume you don't do much installation and have forgotten what you must have known how to do once, at least..?!
Yes ChrisR, you're right,I do very little installation work,more service and breakdown,and a lot more oil than gas,so yes,thats why I may seem a bit rusty but you can rest assured I dont do anything to do with the work unless I am totally sure about it,thats why I asked the question in the first place,I have never been afraid to ask about something if I'm not sure and I think a lot of people are afraid to for fear of looking inferior in some way,even the dreaded corgi inspector doesn't expect you to know everything from the top of your head and tells you to refer to books as thats what they are there for.
I know the general principles of pipe sizing and I know how to refer to books,which I do a lot if I need to,the actual working the size of the pipe wasn't really what my origional question was about,it was to do with the closeness of the tee off after the meter back to the existing BBU and the new pipe going of to the new boiler,I am beginning to wish I'd never asked it now.

#### chr15

doitall said:

The one thing that ACS teaches you is to refer to the course books, and where to find the information.

Either you have the reference books from the course or you are not an RGI.

And in any case, anyone with half a brain would see the answer its so obvious.

Not that worrying,after reading my origional post I can see why you all decided to jump on the 'are you an RGI' bandwagon,it seems such a simple query which I should have already have known the answer to which is of course all appliances have to be taken into consideration,put me off asking anything in the future,I can tell you,anyone can sit there with a book in front of them pretending to be an expert to the unsuspecting person asking the question,starting to feel a bit sorry for some of the diy'ers on this site now cos I know the answers they sometimes get are from some of you guys who like to show how clever you really are,or like to appear to be,carry on feeding your ego's guys.

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