pipe sizing

[jase158]

I am getting a lil confused and cant remember the rule,

when you cant see the pipes you add

1. 10% for fittings or
2. 50% or 1.5 times for fittings,

anybody know where this is in the bpec book as would be better to learn the full rules and read up rather then being told.

also is this for pipe sizing or only purging? this is where I am getting confused.

 

[Simon F]

keep reading and it will/should/might ?? all makes sense
the numbers you have mentioned are to do with calculations for purging volumes.
pipe sizing is more critical as to number and type of fittings potentially making a big difference to resistance

 

[plumber0808]

Read up on it and do some example calculations. It would be tricky explaining it on a post.
I will say that where you can't see the pipes as they are under boards etc..
e.g 28mm then goes under floor then it comes back up somewhere else in 22mm.
It should be worked out as the size it is when it disappears (28mm) up until you can see the 22mm as you can not confirm it is not 28 or 22

 

[plumber0808]

The example above is for purge volumes not pipe sizing. It won't let me edit it?

 

[tamz]

It has nothing to do with pipe sizing.
You need to know (work out) the installation volume (IV)for purging to know what type of purge to perform and also to make sure any additional pipework you may add does not exceed the volume you can work to on a domestic ticket (0.035m3) .
IV is the volume of the pipework (IVp) + the meter if fitted (IVm) + an additional 10% allowance for fittings (IVf).
So
Ivt (total installation volume) = IVp + IVm + IVf (10%)
If it is above 0.02m2 you purge to ignition (ie draw it through a hob or something and continually attempt to ignite) and above 0.035m3 you can't work on it.
Next time you are in the training place have a look through IGE-UP-1B.

 

[jase158]

whats the difference between pipe sizing and installation volume?
Have just saved IGE-UP-1B, thank you, will read that tomorrow night

 

[jase158]

or should I say, what is pipe sizing for?

 

[gasmanrob]

Pipe sizeing is to ensure the appliance gets a constant and steady flow of gas ie if you have a boiler and hob nexus a run of gas pipe you would need to ensure the pipe work can supply the volume of gas required at the rate required. It's the foundations to getting the correct bp or gas rate, a 22mm pipe with a pulled bend and 2 90degree soldered will supply a better stream then say a15 mm with 10 90degree soldered

 

[tamz]

Pipe sizing it to ensure the appliance is supplied with the correct amount of gas at the correct pressure. There is a loss of pressure through each meter of pipe and fitting which is more the smaller the pipe size.
The installation volume (IV) is how much gas is contained within the pipe. You measure the pipe (roughly) and the diameter them look up a table to see how much volume the pipe contains/meter.
eg.
1m of 22mm pipe will contain 0.00032m3 of gas 1m of 15mm contains 0. 00014and a U6 (G4) meter will contain 0.008m3
So if the pipe is 3m of 22mm and 12m of 15mm on a U6 meter you have 3 x 0.00032 + 12 x 0.00014 + 0.008 = 0.01064 + 10% (for fittings) = 0.012 (rounded up). A straight purge but no one will shoot you for purging it through a continuous ignition (hob or the like).

 

[jase158]

right this is where I am confused,

If you can see the pipe installation, you add 0.5 metres for every fitting,

yet you add 10% for each fitting on installation volume.

so if a length of 22mm pipe is 5 metres with 3 elbows, your actual length is 6.5 metres

Installation volume = 6.5 x 0.00032 = 0.00208
or Installation volume = 5 x 0.00032 = 0.0016 + 10% = 0.00016 = 0.00176


do you add 0.5m and add 10% or only add 10% if you can't see the fittings?

and if you cant see the fittings do you add anything to the pipe sizes? or do you leave as they are?

 

[PlumbersMate]

From what I remember you add less for a pulled bend than an elbow etc and even more for tees

 

[dancinplumba]

right this is where I am confused,

If you can see the pipe installation, you add 0.5 metres for every fitting,

yet you add 10% for each fitting on installation volume.

so if a length of 22mm pipe is 5 metres with 3 elbows, your actual length is 6.5 metres

Installation volume = 6.5 x 0.00032 = 0.00208
or Installation volume = 5 x 0.00032 = 0.0016 + 10% = 0.00016 = 0.00176


do you add 0.5m and add 10% or only add 10% if you can't see the fittings?

and if you cant see the fittings do you add anything to the pipe sizes? or do you leave as they are?

One is for the RESISTANCE and one is for finding VOLUME 🙂
.5 elbs an tees .3 for swept bends and 45s is for the RESISTANCE

 

[peteheat]

Agree less restriction on a pulled bend than an elbow, it's been a while but we were told to always pipe sizing charts never to try calculating in your head because there are too many variables?

Maybe there are apps or programs that do it for you today?

Shouldn't be a problem on a standard domestic installations after a while but better safe than sorry.

 

[jase158]

I see now, like water then!!!

so the bend slows the gas down like it has 0.5 metre extra on it,
where as the volume of gas in a bend is roughly 10% of the pipework volume.

so I would work out metres of pipe, "5" in the example above plus 10% for fittings.

need to learn calculations for ACS, will be getting apps when I pass

 

[tamz]

right this is where I am confused,

If you can see the pipe installation, you add 0.5 metres for every fitting,

yet you add 10% for each fitting on installation volume.

so if a length of 22mm pipe is 5 metres with 3 elbows, your actual length is 6.5 metres

Installation volume = 6.5 x 0.00032 = 0.00208
or Installation volume = 5 x 0.00032 = 0.0016 + 10% = 0.00016 = 0.00176


do you add 0.5m and add 10% or only add 10% if you can't see the fittings?

and if you cant see the fittings do you add anything to the pipe sizes? or do you leave as they are?

You are indeed getting confused. 2 totally different things.

The 10% only applies to working out installation VOLUME. This is in regards to your purge volume.

The 0.5m is the length of pipework you add for each fitting (0.3m for a pulled bend) when working out the PRESSURE LOSS for sizing pipework. This pressure loss should not exceed 1mb from the meter to the appliance. The longer the pipe and the more fittings on it the greater the loss of pressure on the gas flow will be.


I'll use your example of 5m of 22mm pipe and 3 elbows.
PIPE SIZING
3 elbows have an equivalent pipe length (EL) of 1.5m so you need to check you can get the amount of gas yo need for the appliance through the pipe size you have without more than 1mb of pressure loss. are based on a straight length of pipe 6.5m long. You look up a table and see how much gas can flow through 6.5m of 22mm pipe and see it goes up in 3m intervals so look at the amount of gas that can flow through 9m of pipe and the table says 4.6m3/hr. If your appliance needs less than 4.6m3/hr the pipe size is fine.
There is a way to work out the pressure exact but don't worry about that for now. It will confuse you even more. Get this bit in your head first.

INSTALLATION VOLUME
The installation volume is the amount of gas inside the pipes, fittings and meter.
On a pipe this length experience would tell you you don't need to bother calculating anything as it will be well under 0.02m3. You would just purge 0.01m3 (5 times the badged capacity or cyclic volume whatever you prefer to call it) but this is how it is worked out.
Use the formula IVt(total volume) = IVm(the meter) + IVp(the pipes) + Ivf(the fittings which you count as 10% of the volume of the pipe)
So
IVt = 0.008 (U6 meter) + (5 x 0.00032)(the pipe) + (5 x 0.00032 x 0.1)(10% of the pipe)
IVt = 0.008 + 0.0016 + 0.00016 = 0.00976m3 so it is just a std 0.01m3 purge.

 

[jase158]

You are indeed getting confused. 2 totally different things.

The 10% only applies to working out installation VOLUME. This is in regards to your purge volume.

The 0.5m is the length of pipework you add for each fitting (0.3m for a pulled bend) when working out the PRESSURE LOSS for sizing pipework. This pressure loss should not exceed 1mb from the meter to the appliance. The longer the pipe and the more fittings on it the greater the loss of pressure on the gas flow will be.


I'll use your example of 5m of 22mm pipe and 3 elbows.
PIPE SIZING
3 elbows have an equivalent pipe length (EL) of 1.5m so you need to check you can get the amount of gas yo need for the appliance through the pipe size you have without more than 1mb of pressure loss. are based on a straight length of pipe 6.5m long. You look up a table and see how much gas can flow through 6.5m of 22mm pipe and see it goes up in 3m intervals so look at the amount of gas that can flow through 9m of pipe and the table says 4.6m3/hr. If your appliance needs less than 4.6m3/hr the pipe size is fine.
There is a way to work out the pressure exact but don't worry about that for now. It will confuse you even more. Get this bit in your head first.

INSTALLATION VOLUME
The installation volume is the amount of gas inside the pipes, fittings and meter.
On a pipe this length experience would tell you you don't need to bother calculating anything as it will be well under 0.02m3. You would just purge 0.01m3 (5 times the badged capacity or cyclic volume whatever you prefer to call it) but this is how it is worked out.
Use the formula IVt(total volume) = IVm(the meter) + IVp(the pipes) + Ivf(the fittings which you count as 10% of the volume of the pipe)
So
IVt = 0.008 (U6 meter) + (5 x 0.00032)(the pipe) + (5 x 0.00032 x 0.1)(10% of the pipe)
IVt = 0.008 + 0.0016 + 0.00016 = 0.00976m3 so it is just a std 0.01m3 purge.

brilliant thank you, got there now

 

[tamz]

Thank fk :lol:

 

[kirkgas]

And to add the next logical step to tamz brilliant explanation is the PV ( purge volume)
Using his formula once you have calculated the total IV you multiply it by 1.5 to give you the amount of gas you need to purge ( flush through) the meter to ensure the gas/air mix is removed

The key values are under 0.02m3 you purge to fresh air WITHOUT lighting
Over 0.02m3 you try to ignite right away
The other significant value is 0.035m3 which is the max IV domestic engineers can work on
Rule of thumb is E6 meter and 60m of 28mm copper, OR 90m of 22mm copper is about the max length you can work on so it's easy to see most houses are well within the max level without a calculation needing to be done