Home ยป ACS Gas Training – How To Size A Gas Pipe

Allen Hart:
ACS Gas Training. Gas pipe sizing. My name’s Allen Hart, and today, I’m a Viva Training Academy, and I’m with Russ, the expert trainer. Russ is going to go through pipe sizing. We’ve got a few charts. This is a question that I get asked quite a lot. When I do my sizing, and I say, “We’re only allowed one millibar drop over the installation,” et cetera on the pipe sizing, and people question that and say, “Well, manufacturer instructions say we can go down to 15 millibar et cetera. People are misreading the instructions.

Allen Hart:
In this video today, Russ is going to go through pipe sizing. Some charts on there. There’s also some charts here with the different sizes for different pipes. Russ is going to go through all these. Also, when you’ve got elbows and you’ve got Ts, how they affect your pipe sizing. This is going to be a very, very detailed video. It’s going to go through the pipe sizing from start to finish really. If you do have any questions about pipe sizing, then obviously, please ask them in the comments below.

Allen Hart:
Yeah, I think that’s it. So let’s go over to Russ. This video is for gas safe registered and trainee gas engineers under supervision. Please comply with the current regulations of the time.

Russ:
Thanks, Allen, for that. Today we’re going to look a pipe sizing. Domestic pipe sizing, we’ll call it on your SES up to the maximum 35 mil. All I want to do today is give you the principles of pipe sizing and show you some simple, straightforward exercises and practises. There are many, many different ways of pipe sizing. Different publications will show you different methods. I am slightly of the old-school, as you may imagine. I’ve done it one way for a long time, but there’s a new method out there, which I’m going to show you today that I’m quite impressed with, and I’ve adopted myself. Different publications of this way show you different ways. This one we’re using from our training manuals at VIVA training. We use logic, but you’ll get the same information out of other publications, example, British Standards, [inaudible 00:02:43], that type of thing. They’ll have the same systems in them. Hopefully by the end of this, and I am trying to keep this simple and break it down as much as I can, you’ll understand where we’re coming from, and why we pipe size, and of course, a simple method of how to pipe size.

Russ:
Pipe sizing, as I hope you know by now, is a very vital part of gas pipe work. We need to supply the volume of gas required for the appliance, but we also need to maintain a tolerance within the pressure range. I’m going to give you round figures so you’ll understand where I’m coming from, so we don’t mess too much on that one. If we have 21 millibars coming out of our metre, on a low pressure system, we should have no more than one millibar drop across the system, therefore no less than 20 millibars going into the appliance.

Russ:
We’re going to do a couple of simple examples of pipe sizing. Remember what we’re saying, we’re looking to maintain pressure, but we’re also looking to maintain that pressure with a volume of gas over a distance. Now the two examples I’m going to show you first are very simplistic, but will show you the difference in how to use the chart initially and how a different pipe size can completely change the pressure loss across that system.

Russ:
We’ve got two different systems here. Very simple, very straightforward. In fact, it’s all straightforward. You haven’t even got any bends. It’s a straight piece of pipe just to show you, initially, the example of that. First of all is 10 metres, 10 metres of pipe, up to 15 kilowatts of load. In other words, that boiler is going to use 15 kilowatts of gas per hour. That’s the idea behind that. You can convert that to metres cubed, but in this particular case, you actually don’t need to. You just work off the [inaudible 00:04:49]. It’s one of those situations.

Russ:
Same with this one. Shorter distance, but now a bigger appliance just to show what different it makes. What you must do on something like this is use a little bit of professional knowledge, if you like, or experience, which I know you don’t have a lot at the moment if you’re in the process, but it will come in time. You get a feel for what size pipe you need to put in. Now, remember, ideally … Not ideally, exactly. If you’ve got 21 millibar coming out of there, you must have no more than one millibar pressure drop across the system. So you should have no less than 20 millibar to the inlet to the appliance, and still supplying sufficient gas to provide 15 kilowatts.

Russ:
The principle behind pipe sizing is quite straightforward once you understand it. What they’re basically saying is, on one size of pipe, they will give you the pressure, a certain volume, through that pipe. What you’ll find from a standard pipe sizing chart, if we were to use 22 mils. Let’s say this is 22 mil copper pipe. Copper pipe makes a difference. A different internal [inaudible 00:06:24] can make a difference. The 22 millimetre pipe over a distance of 15 metres would pass 3.4 metres cubed per hour. To put into more perspective, 15 kilowatt, if you were to multiply that by a factor of 0.095, that will come out at approximately, I’ve already done it, somewhere. There we are. 1.42. 1.42, round figures, metres cubed per hour. So you need to go … It’s good to know load. It’s good to know the actual kilowatt input.

Russ:
So what this is saying, it’s saying 22 millimetre pipe, if I have 21 millibars there, I would have no less than 20 millibars when you get to the other end. Now, this is working pressure. It’s actually the gas moving the appliances on. The appliance is on. 21 going in. 20 millibars at the other end of that pipe. 15 metres. Remember this is an example straight from the chart. 15 metres. Therefore, I like that word. Therefore, if I go approximately halfway along there, believe it or not, I’m going to have 20.5 millibar. If I’m a quarter of the way, I’m going to have 20.75 millibar. And et cetera. If I’m a quarter, 20.25. In other words, the pressure drop across that straight piece of pipe is what you call linear. It’s proportional. The further you go, the more the pressure will drop. The further you go, the more your pressure will drop.

Russ:

Now, the old pipe sizing systems worked on the theory that, if that’s the pipe you’ve picked, and you’re only going that distance, what would you have pressure drop? Quite simply, you’re going to have, I’ll straight up to the top here, from here halfway along, you’re going to lose half a millibar. By the time you get to here, you’ll have lost 0.75 of a millibar. Obviously nearer to the source, you’ll have lost 0.25 of a millibar. So, as you can see, as the distance goes, so does your pressure. As the pressure loss increases, your pressure reduces. That was a bit of a backwards statement, but if you can get your head around that, the further you go, the more pressure you will lose. This is what most of these pressure loss calculations are based on. Don’t get too bogged down by that. Want you to understand it is a proportional pressure loss the further you go.

Russ:
Going back to this one for a second, we’re saying 10 metres, 15 kilowatt. The good news is, a little chart I’m going to show you now, simplifies this. What we talk about when you look at these charts, you’ll find more often than not that they don’t specifically give you the volume or the size that you actually want. So let’s just say, for example, 15 kilowatt, ideally. It’s doubtful the chart will ever give you 15 kilowatt. It will more likely give you, as an example, 14.8 or 15.2 watts. Something like that. So you’ll always go to the nearest one to it, but slightly above, not below. You don’t want to have less volume. You want to have more volume, so you’ve always got something in the background, if you will.

Russ:
We’re going to look at the chart, and we’re going to look at 15 kilowatts. I’ve taken away some of the more confusing parts around there to try and keep it simple initially. We’ll just work on input in kilowatts for the moment so you can see how the chart works. I’ve got two [inaudible 00:10:52]. [inaudible 00:10:52]. The chart shows you three different methods. It shows you both the flow rate, if you wanted to work on metres cubed per hour, but also gives you both gross and net [CB 00:11:10], in other words, the input in kilowatts. For today, we’re going to work on net kilowatts to work our pressure loss.

Russ:
As you come across the chart, you start to get columns of numbers. Across the top of here, you’ll also see pipe sizes across the top. If I were to go up to, literally, let’s just say down here, 51 kilowatts. The load on that, we’ll just do an example. 51 kilowatts, if you come across, as you can see, it doesn’t even show you 51 kilowatts up to 15 mil because you’re going to need bigger pipe than 15 millimetre. 51 kilowatts starts at 22 and goes up to 35. Now the number in each box, that’s on 22 millimetre, the number, it says 0.1996. Now that is the pressure drop in millibars. That’s the pressure drop in millibars per metre run. In other words, however many metres you go, that would be the pressure drop per metre. You’re literally multiplying the distance by the pressure drop per metre.

Russ:
So if we come back up now to this example, I’m going to give you two for each of these examples. I’m going to do it in 15 millimetre pipe, and I’m going to do in 22 millimetre pipe. If I use the chart here, to simplify it again, I find the nearest I come to 15 kilowatt. The nearest I come to 15 kilowatt is 17.9. Like I explained, the charts, if you had a specific chart for every one, it would be pages, and pages, and pages long. So they simplify that by doing it in stages. I cannot tell you why they actually do those specific jumps, but it works. You always look for the one nearest to your volume, or input, or the one above. The nearest one I can find on this chart is 17.9. If I came across now to 15 mil, because I’m going to assume it’s going to need at least 15 mil, going back to that experience thing.

Russ:
Don’t forget, when you work these out, if you wanted to, you could do every pipe size on the sheet. It wouldn’t help you, but there’s nothing wrong with that. So don’t think you’ve got to know which size pipe it is. This is the whole point of doing this. You could do two different sizes, even three if you needed to, but you usually got an idea by this stage what size pipe you’re going to need. Do two different sizes, see what pressure drop you’ve got. See if it works.

Russ:
We’re going to do … Excuse me. Put my pen quick there. 15 mil. Now, 15 mil is 0.1832 millibars per metre run. That’s per metre. So we’re going to multiply it by the distance, 10. That’s going to come to 1.83. I wouldn’t bother too much about more than two decimal points on the actual pressure drop. 1.83 millibar. Straight away, what have we said? We’ve already said that you’re not allowed to have more than one millibar drop. So we know straight away, 15 mil isn’t going to carry that over that distance. Let’s just take you back through that one very quickly. 15 millimetre pipe was chosen. The pressure drop on 15 mil per metre run is, for that volume, for that input, is 0.1832 millibars per metre. So for 15 kilowatt going in, to get that volume for 15 kilowatt on 15 mil pipe, we’re going to have a pressure drop of 0.1832 millibars per metre. If I multiply that by the distance I’m travelling, 10 metres, that comes out at 1.83 millibars. Won’t work. It’s far too much pressure drop.

Russ:
If I take you up to 22 mil. Now, the factor for 22 mil is, very quickly find it again, lost it. Here we go, 0.0311. Now I’m going to multiply that by 10 metres, and we’re going to come in at 0.31 millibars. Now, we’re nicely, comfortably, in fact, within the tolerance of one millibar pressure drop. Let’s go back through that very quickly. 15 mil, factor for that volume or that input is 0.1832 millibar drop for every metre run. We’re going 10 metres. Multiply it by the number. We come in at 1.83 millibars, far too much pressure drop. 22 mil of the same distance, same input, now with factor for 22 mil is slightly less, 0.0311. Multiply it by the distance. Now we come in nicely under at 0.31 of a millibar, just a third of a millibar.

Russ:
The next example is slightly bigger input, but it’s 10 kilowatts more, 25 kilowatt, but over a shorter distance just to show, again, different principle. We’ll say again, 21 millibar, and 20 millibar, no less than at the appliance. Needless to say, we know 15 mil is not going to work out because it wouldn’t carry it for 15 kilowatt. We’re going to start with 22 mil. The factor on 22 mil for 25 kilowatt is slightly different. You come down your chart, it says for 22 mil, the factor is 27 on this one, which is a little bit newer than the other one, 0.0663. There’s an extra five on the end of that one, we don’t really do too much about that one. We always wondered why it’s there. No one seems to be able to tell us. Multiply by eight metres. That would come in at, I’ve written this one down because I can’t remember off the top of my head, 0.53 millibar. So that’s fine. That’s a good pressure loss. Nothing wrong with that, half a millibar. You’ve still got plenty to play with at that.

Russ:
But about if we were to use 28 as an example? 28 millimetre pipe. The factor on that one is 0.0183. We’re going to multiply it again by eight metres. That comes in at, on my reckoning, 0.14 millibars. Let me see there. 22 mil pipe would work, no problem. But there’s very little pressure loss if that was the only appliance, I wouldn’t hesitate to put 22 mil in. If I was going to put extra appliances on later, this is something you’ve got to consider, I might be tempted to say, perhaps half that in 28 mil, and then reduce it to 22. We’ll come to that in a few moments.

Russ:
The pressure loss on that is great, but as I say, if that’s all the appliance you’re going to have, you don’t need to have that much pressure loss. One of the factors that comes into pipe sizing, and it’s a way of the world, unfortunately, you’ve also got to consider cost. Yes, you need enough pressure. Yes, you need enough volume. Yes, you certainly need to build in where possible, future growth, future extension, call it what you will. You may need to want to put more appliances on it sometime. It’s cheaper to put the pipe in now while you’re doing it initially than to rip it all out and put it in again. Just time alone will put the price up. It’s just something to consider if there’s a chance that system could be extended, have I got enough volume there to carry the extra in the future? Just something to be aware of.

Russ:
Going back really quickly. We’ve only got eight metres this time. This time a bigger load, 25 kilowatt. 25 kilowatt on 22 millimetre with a factor of 0.0663 millibars per metre run. We do the eight metres, comes out at 0.53, just a little over half a millibar. 28 on the other hand, slightly less because of the bigger volume, over the same distance, only 0.14 of a millibar. In reality, both those pipes are correct, but it would depend on the system. Do I just stick with 22 or do I put some 28 in because I’m going to make the system bigger?

Russ:
I’ve slightly altered the drawings now to take into account fittings on the system. Again, very simple just to show what difference it can make to a gas supply by putting some restriction. A restriction is, as crazy as it sounds, a deviation or a bend on the actual pipework. What we’re going to use alongside the original chart. I’ve already put these figures in because we’ve already seen those previously. I’ve not put the 15 milli because we’ve already proved that 15 mil won’t supply that. It isn’t going to get any better by putting some restriction in. This one again, same factor. Now it’s 25 kilowatt. The same load. The same drop per metre run, but now, the distance is going to change because of the extra fittings that we’re using.

Russ:
We have a factor for every type of fitting that will cause a restriction. A socket, a straight piece, straight connector doesn’t come into it because there should be, theoretically, very little or no restriction going through it. So we talk about 45 degrees, if you will, that can cause a restriction. A 90 degree bend, an elbow in other words, or a sweat bend. Now a sweat bend is one you would make on the bending machine, or perhaps even if you’re strong enough, you could use a bending screen. We’re not supposed to use those anymore. Using a machine bend, it’s less of a bend. It’s just as much of a bend direction-wise but less restriction. It doesn’t have to hit the end and turn. It sweeps around, so there’s less restriction.

Russ:
Of course, you’ve got to also look at a branch or a T. Call it what you will. Now, if you’re going straight through the T, I’m going to draw it for you so I can give you an example. If you are going straight through the T, in other words, literally straight through it, you don’t count that as a restriction. It’s just the same as a socket. You’re just going straight through it. You only count the T if you do that, in other words, you turn and go up it. If that was a, I’ll be a little more realistic for you. Make that into a proper T. If you did that, that would be a restriction because it made a deviation. Or, if you were coming the other way, get rid of my little blue there. If you’re going that way, that would be class of a deviation because you’re obviously going to have to turn one way or the other. That’s the only times you would count the T.

Russ:
In both systems, we kept the same distance. I’ve kept the same inputs. We’ve got the same factor. All of them, difference is I’ve given you two elbows in both systems. Two elbows at 90 degrees. It’s just a normal, straightforward elbows, but the factor of the restriction of the extra length of pipe that creates changes because of the size of the pipe. So, a 22 mil for example, 22 mil would be, straight off the chart would be, an elbow, 0.6 of a metre extra. So now, because you’ve got this, it’s 10 plus two times 0.6 of a metre. That’s the elbows. One, two. So that would be 10 plus 1.2 metres. So now, our length is 11.2 metres. I’ll come back to this in a second. 11.2 metres. What we’re saying is by putting some restrictions on that pipework, we are physically extending the pipework if it had been still a straight piece of pipe. That extension would account for approximately 1.2 metres extra because of those two elbows.

Russ:
Now, we’re multiplying that by 11.2, not just 10, and we come out at, because I’ve already done this, I do apologise. So that calculates out at 0.74 millibars, which is slightly up from the original. If you remember, it was 0.53. I think it was something like that. But those two elbows cause that extra restriction.

Russ:
Now, I’m going to use the same principle on this one, but I will show you, of course, the two different examples using 22 and 28. I’ve used the same pipe size. I’ve used the same distance, but of course, as the original one, we put the extra two elbows. The factor for the elbows, as I’ve mentioned earlier, is 0.6 of a metre extra for every elbow. So that’s what I’ve done here. There’s the original, that’s the pressure drop per metre run, and there’s the extra elbows. Two times the 0.6, which gives you 1.2. That’s plus, of course, the original eight metres.

Russ:
Now calculating this out, we’re looking at now, of course, 0.0663 multiplied by the new length of 9.2 metres, and that will give us a pressure drop of, I want to be absolutely spot on with this one this time, 0.6 millibar drop. Slightly higher than what it was before, but not by a lot just on 28 mil because it’s that little bit shorter, it carries it. The 28 mil, [inaudible 00:27:08], there’s the extra for the elbows. Notice it’s slightly more than 22. It’s 0.8. Using the same principle, there’s the pressure drop per metre run. That’s going to be multiplied by two times 0.8, which is the elbows, the extra distance for the elbows, which comes in at 1.6, obviously. Plus the eight metres will give us 9.6 metres total length including the elbows, the additional length that the elbows create. So now, we’re going to go 0.0183 pressure drop per metre run multiplied by 9.6 metres will give us a pressure drop of 0.17 millibar.

Russ:
Now, that’s not much more than the other one, but it just shows the principle how it just slightly increased it by putting the extra elbows in. Now, if you notice, that is a little bit bigger jump if you remember from what the figures were before. 0.14, I think it was before. 0.53, I think it was. It took you up to 0.6. That one took it up from 0.14 to 0.17. It doesn’t make that much difference a couple, but you imagine a good length is very often difficult to get anywhere with straight pipe. You’ve got to deviate around corners, especially domestically. It can be a real nightmare sometimes trying to get that length over a distance because people don’t want the piece of pipe straight down the middle of the room for obvious reasons. So you’ve got to deviate quite often. The bends could cause a real problem. It’s just something to be very aware of.

Russ:
In this particular case, we’re using the chart. We’re using the chart for the pressure loss. We’re using the additional chart for the pressure loss per metre run. There are other methods for the fittings. There are other methods. Some systems just say add 10% to the fittings. You’ve got to be a little bit careful on that one. It’s more of a commercial setting. We do use it sometimes on a domestic. I’m going to clean this off now. I want to show you all, because this is very simplistic, I’m going to show you all with two appliances just to show you want difference it can make. I’m going to show you that now.

Russ:
As I said before, I will give you now a little bit of what are multiple system. As you can see, I’ve used the same two appliances, but now I’ve put them onto one system. Remember what we said, 21 millibars coming out of the metre should be no less than 20 going into the metre. That’s saying of this one, there should be no less than 20 millibars going into the metre, sorry, into the appliances. Working pressure. Remember, working pressure. So, you could argue that you’ve now got some, a better way of putting them, critical points. What do I mean by critical points?

Russ:
If I were to letter these, I’ll find a different pen for you so it stands out a little bit. It stands out a little bit. You can say from point A to point B, from point B to point C, then from point B to point D. Now what do I mean by that? What am I trying to get to you? If you look at that now, point B, what must we have at point B? Think about that. What must we have? We must have sufficient gas to feed both appliances at the appropriate pressure depending how far it’s going through. So we don’t know until we work out what the load is. But it’s also important that we’ve got enough gas there for that appliance. Also remember, we need to have enough gas there for that appliance.

Russ:
So using that as an example, remember each appliance is its own pressure group for a better word. So, if I said appliance number one. You’ve literally got A to B, and you’ve got B to C. So it’s critical at point B, you’ve got enough gas to feed both appliances, but you still want enough gas to get to the appliance at 15 kilowatt. Appliance two, I’ll try and write so you can read it better. I’ll go across the point on that, guys, so you’ve got a little bit more room to see what I’m going to write. Appliance number two, you’ve still got A to B, exactly the same. A to B, but now you’ve got B to D. Now, what do I mean? What I mean is, when I work out the pressure loss from A to B, and then I work out the pressure loss from B to C, those two figures added together must come to no more than one millibar. Same over here. When I work those two figures out, they must come to no more than one millibar.

Russ:
Now, the point is here, again, I mentioned this earlier. You do get to a point where you get a feel for what size pipe would do, but that doesn’t mean you can’t double check it against the charts. Do I need to go bigger? Do I need to go smaller? But if we look at this from a logical point of view, it’s critical, I keep saying that, it’s critical I’ve got enough gas there and enough gas there. You could argue that there are one, two critical points on that system. On appliance number one’s system, there’s two critical points. On appliance number two system, there’s two critical points. That sounds a bit strange now. We’ve got to take every appliance as its own group.

Russ:
This is really going to be very simplistic. If I’ve got one millibar, if I divide that by a two, believe it or not, I’m going to get 0.5. Using a bit of a guide what pressure I could have at each of those points. As an example, if I had 0.8 of a millibar drop at B, I’m going to be struggling to get my pressures to each appliance. So when I work the figures out, I really want it to be not much more than that at the worst, and slightly under ideally. That gives me a little bit of [scolt 00:34:34] then for what the size pipework to put into the next length. I hope that makes a bit of sense.

Russ:
It gives us a guideline by counting how many critical points we’ve got on each system. I’m not going to do this, but just to give you a quick example. If I was to put an extra appliance on, now that would be one, two, three critical points. One, two, three. So now, I divide that by three, and that gives me an idea of what pressure drop I could have at each of those points. It’s a simple mechanism that gives you just a little bit of a better idea what you can play with as you work it out. We’re not going to do that first. Let’s not get it too confusing.

Russ:
Right. So, remember, we’re going straight through that T, so we don’t need to count it. We’re going from A to B. Now, the load from A to B is 25 plus 15 is 40 kilowatt. Now using the charts we mentioned earlier, that would if you follow that one there, 40 kilowatt net is 41.75. Logically, considering the size of pipes we’ve already worked out, there’s a fair chance that first pipe’s going to need to be 28 mil. I want to work on that in the first instance, okay. Why am I working on that? Because of the load originally worked out, experience tells me, I might need 28 mil. It might sound crazy. Without working it out first, there’s no other way of choosing which pipe. Now, if I get a sensible pressure drop immediately, I know I’m somewhere near with the correct pipe size. We’ll see what we get. We’ll see what we get.

Russ:
40 kilowatts, look down the chart. 40 kilowatts, I’ll use my little piece of paper again. It works better. 40 kilowatt. The nearest one to it is 41.75. If I come across, the pressure drop on that is, on 28 mil, 0.0382. Remember, that’s millibars per metre run. So now, I’m going to multiply that by five metres. As we did before, exactly the same calculation, but this time five metres. Five times 0.0382 comes to a grand total of 0.34 millibars. Now, that’s ideal. It’s really a 0.34, 0.35. It’s just nicely under 0.5 of a millibar.

Russ:
So if I were to come across here now. Point A to B, 0.34. Well, it’s the same for both appliances because it’s the same piece of pipe. So once you’ve worked it out once, you’ve worked it out. You don’t need to do it again. You’ve already done that. That’s a sensible pressure drop on the first piece of pipe.

Russ:
Now, it gets a little bit more fiddly because I’m going to do this one first just to make it easier. Because we’re coming straight through, and again, don’t forget, guys, this is straight piece of pipe. There’ll be fittings, et cetera, et cetera, but we’re just doing this as an example. Straight piece of pipe from there to there. I’m going to try 22 mil. I’m going to go B to C, and we’re talking 15 kilowatt again now. We’ve dropped down because it’s only feeding one appliance. So the pressure drop on that per metre run would be, B to C would be 0.0311. That would be 0.0311 multiplied by the four metres would give us an answer of 0.12 millibars. That seems okay. Fair enough.

Russ:
Now, if you actually check it with 15 mil because this is the easy thing about this now. That seems a bit low. It seems a bit low as that one, well, how about try it with 15 mil. Tried it with 22, try it with 15 mil. The same thing, but instead of being that factor, it would be five times, excuse me … sorry. I forget. So it makes sense to you guys, 0.8321, which straight away is going to come out at 0.73 millibars. Think about that one now. 0.73 added to the original 0.34 takes us over a millibar. So we know we can’t use, sorry about that. Maybe that will make more sense. 22 mil. 0.073 millibars added to the original 0.34 millibar … 0.34, 0.73 takes us over the one millibar. So we can’t use 15 mil.

Russ:

It’s as quick and as easy as that just to double check your figures. If you think that you need to go bigger or smaller, it’s just nothing. Just come back along the line and try the next factor. That’s all I did. Originally, I did 0.0311 on 22 mil. Move there, sorry about that. We’re at 25 mil. 25. There they are. 15, sorry. 15 better than that. 0.0311 from there, and then I’ve come back across and checked it on this, it’s actually 0.1832, sorry about that. But that one comes out the same at 0.73. Okay, 0.73.

Russ:
So those two added together are over one millibar drop. You can’t have 15 mil. So we now have proof to myself by doing that, I’m going to have to go with 22. So I now can go B to C, and put 0.12 in. So my answer’s going to be 0.46 of a millibar. Now, sometimes that happens. Sometimes it comes out because of the other appliances on the group, you’ve got to put a bigger pipe then a smaller pipe. Sometimes it comes out at a very sensible pressure drop.

Russ:
We’ve gone to the next appliance. Don’t forget, we’ve already done the first piece of pipe. This one’s much more involved. Much more involved. Just going to put a line down so we can split it up. Now, I’m going to do B to D. Now, straight away, I’m going to assume again, I want to make an educated guess and say 22 mil. Now, the factor for that input, 25 kilowatts on 22 mil is, just going to check my figures, 0.0663. That’s millibars per metre run, but not just as simple as that this time remember. This time, we’ve got six metres of pipe plus one elbow at 22 mil. If you remember that one we did before, turn that over, one elbow at 22 mil copper 0.6 metres. All right. Sorry. Plus, of course, we’re now doing a deviation through the T. So if you’re going through the T and out, it’s actually a 1.8 metre increase in length. So now, our total length is, I’ll work out the math today. Sorry, guys. It’s not working. Our total length is 8.4 metres. I do apologise. 8.4 metres.

Russ:
So now, we’re going to go 0.0663 multiplied by 8.4 metres. That comes in at a nice 0.55 millibar drop. So now, if we jump further across to there, 0.55, our pressure drop is a very nice round 0.89 millibar. Remember, we can’t have more than one millibar. That’s spot on. Lovely distance. Lovely pressure drop. We’re nicely within tolerances.

Russ:
If, again, you wanted to check that, you could check it up to, that was 22, of course. If you wanted to check it, you could check it up to 28 millibar, sorry, 28 mil pipe. At 28 mil, I think you will find it comes out at, if I find the factor for that very quickly, 0.0183 multiplied by, you’ve got to be careful on this one, it changes, with our six metres plus 0.8, remember for the elbow because we’re now on 28 mil, not on 22 mil, and a staggering 2.3 metres extra for the T, the branch.

Russ:
So now, we’ve got six, seven, eight, 9.1 metres. So 0.0183 multiplied by 9.1 metres will give us, and I haven’t actually worked that one out. Just to show you, 0.0183 multiplied by 9.1, 0.16 millibar. Which, if you were to put that to the 0.34, it would give you some scolt for extending, but would be a very expensive way of running that final supply to the appliance. Again, I mentioned this earlier, you’ve got to be a little aware what is it costing you to do this job? If it’s the last pipe on the line, I’d be very dubious of putting 28 milli if I didn’t need to.

Russ:
Just run through this really quickly again. Because we’ve got the two appliances, we could argue we’ve got one, two critical points going to that one. One, two critical points. One of the problems people have is getting their head around the one millibar is individual to each appliance. It’s not two millibars across the system. It’s one millibar to each appliance.

Russ:
Now, sometimes, what you can get is if you’re working this out, in reality, you might not … Because this just happens that works out quite nicely, but depending on what the system is, you might not want 28 milli that full distance. You might just put one length of 28 milli, three metres. That surprises how much difference that can make to your pressure. Let’s just say you would change it, just as an example, from there. That would become, technically, another point of reference. You could say, you’ve got A to B, so you could say that one A to E. You could see what pressure you got to there, and then reuse it down to the next pipe. You’ve gotten so you could work it out from that as a pressure drop because as soon as you reduce the pipe size, you’re going to increase the pressure loss. You’ve got to take it into account that’s an additional point in your pressure.

Russ:
Most of the time, I don’t want to confuse you on this one today. Just keep it simple. Let’s just keep it simple. We’re using one piece of pipe up to the point there. We’ve got to have enough gas there to feed both pipes, both appliances, both pipes down to the appliances. When we worked it out, it came out at using 28 millimetre pipe. 28 mil anyway. 0.34 of a millibar drop. 0.34 of a millibar drop. As I say, once you’ve worked that piece out, it’s the same piece of pipe for both appliances, so you’ve already done it.

Russ:
Then you’re going B to C. 15 kilowatt, I’ve dropped it down there to 22 mil. Somewhere down here, 22. That’s 28. We’ll just put 28 there. 28. 28 mil. Then we’ve dropped it down to 22 mil. Those two added together come to 0.46 of a millibar, just short of half a millibar. The other one, using the same pipe sizes, now, they come out to a really nice round just short of 0.9 of a millibar. Just nicely inside that one millibar.

Russ:
It’s something that you need to do a few of to get your head around them. I’m not pretending this is a very quick overview. Once you understand the principle of being able to jump from one column on your chart, from one column to the next, you can quickly prove do I need to go bigger to give yourself a nice cushion? Or do I need to go smaller to get, I don’t need to have so little pressure drop. I can get away with a little bit more pressure drop. Remember what I said about the 0.5. That one was nicely inside, to B, 0.34, but actually, that one was over half a millibar. So you see what I mean? Because I’ve got less than half a millibar there, I knew I could have slightly more than half a millibar on either of these two.

Russ:
It’s not something that’s simple to take in first time. Hopefully, it will start to sink in the more we do this. We need to practise. There are some examples in most training manuals anyway. Certainly are some in ours. It’s something you can make up your own systems and try it. You’ll realise straight away quite often that you can’t actually do what you’re trying to do without putting a big silly pipe at the front. It’s something that you just learn to understand. I cannot tell you how to do this. You need to just practise it, and practise it, and practise it. That’s the principle.

Russ:
As I say, if you can get your head around this chart, it’s such a simple mechanism this. That’s the distance. That’s the load. What’s the pressure drop per metre run? You multiply that by the distance, and that gives you your pressure drop over that distance. I am, as I said earlier right in the beginning of this, I’m a bit of a, I’m not going to say a [inaudible 00:50:35], but I’m certain I’m not far off. I’m certainly into the old fashioned systems. This, I think, is a really, really simplistic, very accurate. It works out very close to the other system. Some time, most of the time, just as accurate. And an easier one to follow when you try to work out your pipe sizes. I think if you get your head around it, you will, will understand it better.

Russ:
Thanks for watching this anyway. We will get you some more examples if possible. Thank you very much.

Allen Hart:
Thank you for that, Russ. I hope you found this video of some use. Bear in mind, you will need this sort of stuff for your SES gas assessments, but if you do have any questions, please ask them in the comments below, and we’ll try as best to answer them, and maybe come back and do another video on pipe sizing or whatever type of video that you would like.

Allen Hart:
Thanks for watching.

Allen Hart

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