If I could I would lol it’s the factor that they use for the water volume it made no sense to me either but that’s what is used.

@@tomkatgastraining Also 0.5x0.2=0.1 not 0.7.

@@tonysmith7028 if you watch the video you will see I put the mistake on the screen that you add it not times it and I even say later in the video about the mistake

Yes the water stays in the vessel and the air in the vessel keeps the pressure behind the diaphragm so when the water cools the air pushes the diaphragm down again

I could put that on the to do list 👍🏻

Just about to make same comment, 1.3 is 30% expansion

I thought I would see if anyone else had spotted that and I'm glad someone did. I know the general rule is to size CH expansion tanks at 10% of the system volume and most people say that that is conservative. It also seems that most heating engineers oversize both radiators and boilers, but that's another topic.

@@robi4387 thank you for your very great videos and Chanel. Can I suggest a topic for video? Basically, I came across this situation that I have been asked to do a cp12 for an office and they asked me if I am commercial engineer and I explained that what commercial mean in gas industry, had another situation that it was a commercial property and I doubt it that is the gas pipework needs to be labeled or not, another situation was they joined two offices together and they had two meters but the total kw was more than 70 but pipework was 22mm because they fed from different meters and I didn't know if I can do it and raised it with gas safe and they said I can do it. I am sure you will find other situations related to the commercial and can make another great video about it.

yes..

The megaflo has a built in expansion vessel for the hot water and a system boiler has a built in expansion vessel for the primary water to heat the cylinder and radiators. They are separate waters so need the 2 vessels

It’s a figure the manufacture came up with for the expansion of the water so 3%

@@tomkatgastraining Thanks for the clarification

@@tomkatgastraining 3% is 1.03 not 1.3. 1.3 would be adding 30 percent not 3 percent.

@@jamesabdilla is correct. The calc should be 1.03 not 1.3. 1.3 is 30% expansion

I think that if you install the vessel higher than the cylinder a use copper pipe and not flex’s there is not much chance of getting legionella.

It has to be as accurate as you can get it or the vessel could be to small and you get more than a 0.5 bar increase. I don’t know of any rule of thumb for the volume but most combis are set up for about 130 to 140 litres

@@tomkatgastraining Hi Derek, thanks for the video and this snippit of info.

I had to work out expansion on a system using something similar to this on a large commercial heating system a few years ago. They’d had new boilers, and someone had noted they had no expansion vessels. He was correct, they didn’t, but what they had was a buffer tank of water filled by a float valve. When the system heated up the expansion was controlled by a pressure switch opening a solenoid valve dumping the increased water volume into the buffer tank. I explained this to the engineer reporting no vessels, but he was adamant about there being no vessels. I left him to run with it ( he was my supervisor), and he put in 2 small vessels prob less than 100L total. He ditched the buffer tank, so, when the system expanded from cold the system kept shutting down due to high pressure. I was asked to look at it. I’d not done anything like that for decades, and after a lot of googling came up with a figure of ( roughly from memory) 420L. When I submitted it to the customer ( the local authority ) their engineer just said “we operate on 1 litre of expansion required for every 1 KW of output of the heating systems boiler/s” to which they ordered up 2 x 300L expansion vessels. They went in and there’s been no further issues since. Talking to other commercial engineers since, the 1L for 1KW seems to be an accepted way of calculating vessel sizes on large unknown heating systems.

Tut tut that would only happen it the Schrader valve is at the bottom of the vessel as the water is heavier than air so sinks to the bottom of the vessel. Should have mentioned that me thinks but average comment makers only go for the negative.

@@tomkatgastraining Yea we also need to know the difference between Negative Remarks and Good Constructive Criticism

Yes, should have been 1.03 not 1.3!!!!

When you do the calculation it works out at 6.18 Lts (Not 7.8) Which is 4.12% not 3%