Location of Sealed System Components

[Andy Hall]

On Sat, 15 Jul 2006 20:29:19 +0100, Doctor Drivel wrote (in article ):

Ar you on commission?

[Doctor Drivel]

I don't work for sharks.

[Andy Hall]

On Sat, 15 Jul 2006 21:32:25 +0100, Doctor Drivel wrote (in article ):

I see. Who do you work for?

[Doctor Drivel]

Matt, not sharks.

[Ed Sirett]

There is I beleive a BS for this. I suppose it might be useful to obtain a copy someday. However most boiler installation instructions are somewhat schematic in this area, many favour putting the vessel on the return (probably because the pump is on the return in the boiler.

The Potty Suprima wants the components on the flow before the external pump.

My guess is that th expansion vessel before the pump makes sure that the pump operation increases rather than decreases internal pressure in the circuit.

[Andy Hall]

On Sun, 16 Jul 2006 00:08:35 +0100, Ed Sirett wrote (in article ):

Thanks Ed.

This is somewhat akin to Andrew's point, I think.

I have to drain my system to exchange a radiator for a different type in a different place, so while doing so decided that some moving of these components would be useful too. I can easily position the vessel appropriately, but wanted to make the tee in for filling in a different place. I can't see a reason why the two can't be separated, but thought I'd ask in case there was a specific regulatory reason.

[Ed Sirett]

I usually let others take the load on the futile process of DD's education in physical laws....

The expansion is not caused directly by the boiler (i.e. by the boiler growing smaller say) but because the water in the primary circuit - all of it - expands as it gets warmer. As it says in the FAQ (which you claimed was so 'incomplete' you refused to read it) the expansion is about 2.5% between 25C and 75C.

Obviously in some sense the boiler is the cause of the water getting hotter and thus the expansion of the water. However, there is nothing different about the expansion of the water in the boiler relative to that in the pipework or radiators. Furthermore the bulk of the water is not in the boiler.

The pressure in the primary circuit is affected by three things

1) The current pressure in the expansion vessel. 2) The height of any part of the circuit relative to the vessel. (increases c. 0.1 bar /metre of height difference). 3) The differential pressure introduced by the circulating pump.

It would be unhelpful to place the relief valve at a great height difference to the boiler. The manufacturers instructions are the final arbiter in the matter, anyway.

As mentioned before the expansion is a property of all the primary water not just of that in the boiler.

[Ed Sirett]

It's in the links below. Section 5.4.3 contains the answers to this thread unless the manufacturers say otherwise.

[Ed Sirett]

That is only the instructions on some models. Other models say other things.

HTH

[Ed Sirett]

It certainly is often convenient to put the expansion vessel in the loft when "rolling you own" sealed system.

[Doctor Drivel]

Are you serious? The source of the expansion is not the boiler? What is it then. Some old man with foot pump?

The source of the heat and the place were it is hottest is....the boiler? You must be in a different world to me if you think otherwise.

Gosh some figures. The FAQ is fine if it is 1986..but I looked at the calendar and it wasn't. You have no idea of what way the industry is going, what people are buying and what is available. It may be around your street but is around elsewhere.

Like those in the south who say microbore doesn't work while in the north of the country it is the norm.

You don't say!!!!!!!!! Wow!!! The boiler!!!! Gosh.

The greatest expansion and the expansion starts there.

They always put it right on the boiler. Get it quick at its source.

The expansion is greatest around the boiler. Even a sealed system has different pressure around it. Put the expansion vessel where the greatest expansion would be - the boiler.

I've actually seen an expansion vessel before and after the boiler. On a small commercial system. It looked like someone screwed up somewhere so they spit it. It worked.

[Ed Sirett]

Looks like BS 6798 is not worried about the location of the filling loop.

[Andy Hall]

On Sun, 16 Jul 2006 08:17:52 +0100, Ed Sirett wrote (in article ):

Good. Thanks for that, Ed. I couldn't see a reason that it would matter.

I am now seriously concerned about the vessel location. I think I'd better remove one of the kitchen cupboards so that I can fit it high on the wall next to the boiler flow within a few cm of the boiler itself. Do you know if Plumbcenter offer expansion vessels in Farrow and Ball colours? ;-)

[Andrew Gabriel]

All the water in the system, which is mostly in the radiators and pipework. It happens even when the boiler isn't on, e.g. if the house temperature climbs from say 18C to 28C on a hot day, the water expands proportionally and is taken up by the pressure vessel.

Oh, most definately. I live in the world governed by the laws of physics.

[Andrew Gabriel]

Is that shortly before the pump (external I presume)?

What about fitting it inside one of the cupboards?

Also, if my hypothsis is correct, then it would appear your boiler has not been affected by low pressure lockout, in which case moving it would not seem to be required in your case. Another option would be to leave it where it is, and add a small one in the pipework at the desired location (which would use up even less cupboard space).

[Andy Hall]

On Sun, 16 Jul 2006 09:22:53 +0100, Andrew Gabriel wrote (in article ):

I was thinking of taking the pump out of the boiler, and fitting it directly to the expansion vessel on the wall and near the flow pipe. That way I can be sure that the extra expansion on the flow side of the boiler is properly catered for ;-)

A work of art like that.? Should be on full view :-)

There have been no lockouts at all. This may be because the boiler starts the pump slowly and ramps up the speed. I have a convenient space, not too far from the boiler at floor level which is not otherwise usable for much so it can go there.

[Lobster]

Hang on a mo. If there is a massive, rapid expansion (explosion?) at the boiler, it will indeed take time (albeit small) for that pressure increase to be transmitted down the pipework to the HW cylinder, won't it? I'd have thought that the pressure relief valve would indeed be best sited near the boiler in this instance.

Having said that, how likely is an exploding boiler? Isn't it more probable that a thermostat or valve could fail, causing a gradual, simultaneous pressure build-up across the whole system? Under those circumstances it is the cylinder which is the main source of danger because of its relatively massive volume, as shown by the video clip of one exploding which Drivel likes to post from time to time.

David

[Doctor Drivel]

The source of the expansion is not the water in the rads, it is the boiler, the heat it emits. Did you get that?

18 to 28C is very different from 18C to 82C in very short time.

He says the souce of the heat is not the boiler. Mabe someone has sneaked in a nuclear device, if it is not the boiler. He says it is not hottest around the boiler. Maybe it is hotter around some nuclear device in the loft? Mmmmmm

Not going on any further. Maybe he has been admitted to Richard Cranium's institution.

[Mike Tomlinson]

In article , Doctor Drivel writes

In other words, you don't have a reference and are making it up as usual.

[Doctor Drivel]

You got it.