Pipe sizing questions

[JLS]

Hi all, still working on my portfolio but having a bit of confusion regarding allowances for fittings when working out pipe size requirements as I'm reading conflicting information. In college we were told to allow 0.5m for Tees and elbows and 0.3m for bends. My Viper gas handbook says the same but only up to 28mm but doesn't say anything about 35mm, whereas my BPEC book gives completely different values going as high as 3m for a 35mm Tee with the flow exiting into the branch. I appreciate that it's the end result that is important and so long as there is less than 1mb drop at the appliance it will be fine but I'd like to be able to be sure the installation designed is going to work before I put it in.
The specific case I'm looking at is proving quite tricky to me as its an extended bungalow with two boilers, one at one end, the other in the middle, a cooker in the middle but on the opposite side and the meter at the other end so the runs are rather long.

 

[king of pipes]

Here you go bud this is from bepec core domestic gas safety learning manual . Cheers kop

 

[JLS]

Thanks Kop, but that's the information I was referring to. I was wondering if the BPEC manual used different values as it uses a different method. Unfortunately I can't try the calculation using their way as my max flow rate is 6.95 m3/hr and outside the table range given and I can't justify the £200+ for BS6891

 

[fixitflav]

In college we were told to allow 0.5m for Tees and elbows and 0.3m for bends.

Can you elaborate? The way I've heard about is to allow a certain number of pipe diameters for a fitting eg 60 diameters for a tee or square elbow, 40 for a rounded elbow etc. So the equivalent length of pipe varies with the pipe diameter. As you'd expect if you look at the theory.
I can see why gas installers want to use pressure drop tables, but I prefer to use

where f = friction factor, from a table or formula, but usually in range 0.005 - 0.007, sigma n = number of velocity pressures for fittings, rho = density.
Or, using equivalent pipe length

which shows why the equivalent pipe length is a number of diameters, as the D cancels.

 

[ShaunCorbs]

any good?

ive got the viper one but its the same upto 28mm

0.3 bend
0.5 elbow
0.5 tee

 

[JLS]

Can you elaborate?
The way I've heard about is to allow a certain number of pipe diameters for a fitting eg 60 diameters for a tee or square elbow, 40 for a rounded elbow etc. So the equivalent length of pipe varies with the pipe diameter. As you'd expect if you look at the theory.
I can see why gas installers want to use pressure drop tables, but I prefer to use
View attachment 34406
where f = friction factor, from a table or formula, but usually in range 0.005 - 0.007, sigma n = number of velocity pressures for fittings, rho = density.
Or, using equivalent pipe length
View attachment 34407
which shows why the equivalent pipe length is a number of diameters, as the D cancels.

1.Not really we were just told to use .5 and .3 no mention of it varying with pipe size
2.So that's another figure to play with !
3.Looks impressive but I have no idea where to find that information

 

[JLS]

any good?

ive got the viper one but its the same upto 28mm

0.3 bend
0.5 elbow
0.5 tee

View attachment 34410

Is that from BS 6891 Shaun? I'll have a look at the BPEC method using those figures and see if I can make head or tail of it.

 

[ShaunCorbs]

Is that from BS 6891 Shaun? I'll have a look at the BPEC method using those figures and see if I can make head or tail of it.

yes it should be but you also have to look at which way the tee is feeding

 

[king of pipes]

Draw a diagram and post the question on here bud lets have a look . Kop

 

[fixitflav]

1.Not really we were just told to use .5 and .3 no mention of it varying with pipe size
2.So that's another figure to play with !
3.Looks impressive but I have no idea where to find that information

From Shaun's table I worked out ratio of equivalent length to dia for Types 3 and 5 below. Used the steel pipe diameters, as the actual bore is reasonably close to the nominal size. As you can see, the ratios are fairly constant, and fairly close to what I said earlier (the variations aren't due to actual differences in pressure drop, the figures in the table will be rounded, and it's not an exact science anyway).

So I think it would be more useful to give one figure for number of pipe diameters for each type. It wouldn't take long to memorise most of them! But if that's the way the gas industry wants to do it...........
Also if you're designing for 1mbar pressure drop, you know the flow and have calculated the effective length (actual length + fittings equivalent, based on an assumed diameter) you could use the table to find the smallest pipe dia which meets the required flow at the effective length (and iterate if the pipe size is different from the initial assumption). But to calculate actual pressure drop for a given flow, diameter and length would need a bit of thought.
I'm with kop, if you post a sketch we can have a look at it. But include your anticipated pipe sizes, can't speak for kop but I don't want to design it from scratch.

 

[RoryD]

Can you elaborate? The way I've heard about is to allow a certain number of pipe diameters for a fitting eg 60 diameters for a tee or square elbow, 40 for a rounded elbow etc. So the equivalent length of pipe varies with the pipe diameter. As you'd expect if you look at the theory.
I can see why gas installers want to use pressure drop tables, but I prefer to use
View attachment 34406
where f = friction factor, from a table or formula, but usually in range 0.005 - 0.007, sigma n = number of velocity pressures for fittings, rho = density.
Or, using equivalent pipe length
View attachment 34407
which shows why the equivalent pipe length is a number of diameters, as the D cancels.

Are you serious?

 

[fixitflav]

Are you serious?

About what?

 

[Last Plumber]

Hi all, still working on my portfolio but having a bit of confusion regarding allowances for fittings when working out pipe size requirements as I'm reading conflicting information. In college we were told to allow 0.5m for Tees and elbows and 0.3m for bends. My Viper gas handbook says the same but only up to 28mm but doesn't say anything about 35mm, whereas my BPEC book gives completely different values going as high as 3m for a 35mm Tee with the flow exiting into the branch. I appreciate that it's the end result that is important and so long as there is less than 1mb drop at the appliance it will be fine but I'd like to be able to be sure the installation designed is going to work before I put it in.
The specific case I'm looking at is proving quite tricky to me as its an extended bungalow with two boilers, one at one end, the other in the middle, a cooker in the middle but on the opposite side and the meter at the other end so the runs are rather long.

If you use the info in the charts @ShaunCorbs and @king of pipes gave you, you should be fine. You won't be using sizes above 35mm Copper on domestic anyway and even if you do, you won't be able to use much of it.

Or am I missing what you're after?

 

[king of pipes]

I would more concerned at not going over 60kw input with two boilers and a gas cooker , two combis and a range cooker? will be boarder line 35mm is the maximum size pipework you can fit on a domestic ticket so 2 things to think about and don't forget to fit a purge/ test point at each boiler so you can test the true pressure drop across the carcass , kop