Unvented Cylinder Vs Tradiotnal Vented - Did I Do This All Wrong?

[Millwright]

You can't drop that statement without some supporting link to the source?

Well I did.

 

[wundaboy]

What I don't think has been asked, or the OP has said - is what exactly is the problem being experienced with their vented pumped system that leads them to believe they'd be better off with mains fed unvented?

 

[LeeJC]

Having watched the YouTube video at 0.25 speed on my 4K laptop screen, I seem to see something different to you.

Let's assume that the top and bottom of the cylinder are "attached" to the cylinder using similar construction methods, ie, it is a tube with a top and bottom fitted, and let us also assume that the lids and base are the weakest points. Why would the bottom fail before the top? If the top failed, it would be a copper lid (alone) that hits the ceiling above (and lots of water spraying up and, invariably outwards).

Sorry, I don't understand why the underside- exclusively, will fail and not the top or sides.

I am willing to suggest that the video is not (possibly) completely truthful.

I've not seen the internal construction of the cylinder to make this a 'factual' statement but I work in a field that deals with explosions.
It's almost impossible to create seals on this kind of assembly that are identical. This causes one or other of the material joints to be weaker than the others.
I think the point to understand is that the failure and subsequent rapid expansion happens sufficiently quickly to not cause other joints to fail (we use this fact when designing explosive charges that are required to be directional) the only difference being we have to design in using materials/engineering assurance that the explosion occurs in the anticipated direction.
For this example it's entirely probable that they 'managed' the direction of explosion for maximum effect, wouldn't have made such a dramatic film if the top to bottom tube seam had gone 'Phut' and flooded the downstairs.
Don't get me wrong these things can be dangerous if the safety devices are over ridden, but to call them bombs is mostly fear mongering.
A bomb deals with a material burn that creates a vast and rapid expansion of gas 'in all directions < important', a hot water cylinder would as is seen in the video and the one that mythbusters did a good while ago always contain a volume of water which is to all intents and purposes incompressible.
An exploding hot water cylinder is more akin to a f@#kin big hot bottle rocket than it is to a bomb, but with the unpredictability of not knowing where/how it will fail.

 

[Johntheo5]

What I don't think has been asked, or the OP has said - is what exactly is the problem being experienced with their vented pumped system that leads them to believe they'd be better off with mains fed unvented?

Post #15??

 

[Madrab]

I didn't say it couldn't happen, what I said was, that is is unlikely to happen without intervention of safety devices, hence the UV cylinder isn't inherently dangerous, much like a gas boiler, but tamper with it and it may well become unsafe, with consequences.

wouldn't happen in a domestic setting

Sorry but you did, hence my response. If you hadn't, I wouldn't have said anything

what exactly is the problem being experienced with their vented pumped system that leads them to believe they'd be better off with mains fed unvented?

I have to say that I am not that happy and think I made a huge mistake - It would have saved space and been cheaper and pressure would have been better and would have been more fancy. The pump is also noisy when it operates

 

[Madrab]

Sorry, I don't understand why the underside- exclusively, will fail and not the top or sides.

I am willing to suggest that the video is not (possibly) completely truthful.

Never actually seen how one is made but it may be the same process of how other cylinders are made whereby a blank is pressed out of steel so it only has one open end, the coil etc is then installed and then base is welded on, therefore that's the weak point?

 

[JackK]

Is it worth removing a new coffin tank, hot water vented cylinder and pump and installing an unvented ? That was my question in summary

 

[stem]

From the replies it appears subjective. A bit like asking 'Should I buy a petrol or electric car, or should I holiday in the UK or overseas?' folks will base their comments on their personal view and what matters to them personally. And what's right for them, may or may not be right for you.

Same here. It comes down to you and your personal preferences. After reading the input above, you should be able to decide was is and isn't important to you and then make your own decision.

 

[Johntheo5]

Ensure mains dynamic flowrate & pressure adequate, 20LPM at 3bar??.

 

[Millwright]

Sorry but you did, hence my response. If you hadn't, I wouldn't have said anything

No need to apologise, but I didn't, hence me quoting the entirety of what I said, not just your selected reading ability. Also, no need to lie and edit posts is there, come on.

There's more than just the safety devices being capped there.....wouldn't happen in a domestic setting, as you'd have to bypass all cylinder safety and also have a boiler which heats water past boiling point, which they don't.

 

[Madrab]

No need to apologise, but I didn't, hence me quoting the entirety of what I said, not just your selected reading ability. Also, no need to lie and edit posts is there, come on.

Hahah ... yeah right ... apologise .... as if ... get the context right.

Jeesh ... grammer lessons on a DIY forum, whatever next.

Unfortunately the statement was that "it wouldn't happen" it doesn't matter follows it. By using the contraction 'wouldn't' meaning 'would not' it means that - a certain thing will not happen - i.e. there is 0/none/nada % chance that it will happen regardless of what text follows it, hence why that was the only quoted part of the comment, the rest of it doesn't matter. That there is 0% chance though is quite simply not the case. There is a chance, however small/unlikely, that the safety devices on an unvented could fail at the same time either be innocent or malicious interference and there is a run away heat source. Not being very specific on a DIY forum can be fraught with risk as there are people that will believe anything and act incorrectly on the back of it.

Edit posts ???? I don't think so , I didn't change any wording, I only quoted the section relative to the comment, happens all the time in here.

Anyways ..... Apologies @JackK for the digression

Is it worth removing a new coffin tank, hot water vented cylinder and pump and installing an unvented ? That was my question in summary

If you have an adequate min dynamic mains pressure and flow (As per @Johntheo5 suggests) and a suitable location to allow a 22mm mains supply to be run to it then an easy path/access to run the D2 safety discharge pipework to a suitable internal drain or external space, then yes and unvented could be considered.

 

[JackK]

Hahah ... yeah right ... apologise .... as if ... get the context right.

Jeesh ... grammer lessons on a DIY forum, whatever next.

Unfortunately the statement was that "it wouldn't happen" it doesn't matter follows it. By using the contraction 'wouldn't' meaning 'would not' it means that - a certain thing will not happen - i.e. there is 0/none/nada % chance that it will happen regardless of what text follows it, hence why that was the only quoted part of the comment, the rest of it doesn't matter. That there is 0% chance though is quite simply not the case. There is a chance, however small/unlikely, that the safety devices on an unvented could fail at the same time either be innocent or malicious interference and there is a run away heat source. Not being very specific on a DIY forum can be fraught with risk as there are people that will believe anything and act incorrectly on the back of it.

Edit posts ???? I don't think so , I didn't change any wording, I only quoted the section relative to the comment, happens all the time in here.

Anyways ..... Apologies @JackK for the digression


If you have an adequate min dynamic mains pressure and flow (As per @Johntheo5 suggests) and a suitable location to allow a 22mm mains supply to be run to it then an easy path/access to run the D2 safety discharge pipework to a suitable internal drain or external space, then yes and unvented could be considered.

Thanks - Just a final piece of info

Would an unvented cylinder perform equal or better to a 3.0 bar pump shower? What I mean is if I took it all off would it be better, the same or worse?

 

[Madrab]

Would an unvented cylinder perform equal or better to a 3.0 bar pump shower

Again, depends on the mains and the shower - If you have a mains delivering 20L/min @ 3 bar dynamic then yes it will be as good as. Don't forget though there are very few shower that will deliver that amount of flow and if it did then you'd probably drown yourself or strip the skin off your back

There is a point when a shower becomes too powerful and does get uncomfortable. I've found that around 15L/Min @ 2-3 bar more than enough for most people, it also leaves capacity in the system so there is little drop off when more outlets are used simultaneously.

 

[JackK]

Hahah ... yeah right ... apologise .... as if ... get the context right.

Jeesh ... grammer lessons on a DIY forum, whatever next.

Unfortunately the statement was that "it wouldn't happen" it doesn't matter follows it. By using the contraction 'wouldn't' meaning 'would not' it means that - a certain thing will not happen - i.e. there is 0/none/nada % chance that it will happen regardless of what text follows it, hence why that was the only quoted part of the comment, the rest of it doesn't matter. That there is 0% chance though is quite simply not the case. There is a chance, however small/unlikely, that the safety devices on an unvented could fail at the same time either be innocent or malicious interference and there is a run away heat source. Not being very specific on a DIY forum can be fraught with risk as there are people that will believe anything and act incorrectly on the back of it.

Edit posts ???? I don't think so , I didn't change any wording, I only quoted the section relative to the comment, happens all the time in here.

Anyways ..... Apologies @JackK for the digression


If you have an adequate min dynamic mains pressure and flow (As per @Johntheo5 suggests) and a suitable location to allow a 22mm mains supply to be run to it then an easy path/access to run the D2 safety discharge pipework to a suitable internal drain or external space, then yes and unvented could be considered.

What I am thinking is to remove the coffin tank and use the discharge pipe that the coffin tank had in the loft to the outisde of the property as the potential location of the vented cylinder - It has 22mm coming into the coffin tank, the discharge is via the overflor pipe in the loft and so all I need is flow and return to the loft and I am done

In fact it is easier because the vent pipe that was used for the vented cylinder can be joined to the unvneted tank and all hot water circuts will be primed

of course I know you need a G3 engineer but that is the theory

Am I a million miles away because I couldl lay it all out so the engineer can just install and do the building control notic

 

[Johntheo5]

What I would suggest just now to get a feel for your requirements.....

Ensure the HW cylinder is fully heated.
Run one shower only at your normal showering temperature but at full flow, hold a bucket/container under the showerhead for exactly 30 secs, measure this (later) with 1L container and X2 to give you the flowrate in LPM.
Run both showers together and carry out the same procedure, maybe measure both shower flowrates (both on).

The pump curves will then show the actual head required and the additional head required to allow for the elevation/pipe loss between ground floor and shower location can be reasonably calculated and added on.