I've learned a lot as well. Up until this dilemma ive never needed to do these calculations.
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How can I cure my gravity circulation problem?
- Thread starter Neville Hillyer
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View the thread, titled "How can I cure my gravity circulation problem?" which is posted in Central Heating Forum on UK Plumbers Forums.
I've learned a lot as well. Up until this dilemma ive never needed to do these calculations.
You never should need to - it is a theoretical exercise anyway unless you know the friction factor of the coil.
My view is that identifying the cause will not change the most cost effective remedy of converting to a pumped system.
With respect to Telford, I have always found them very responsive and quick to offer a substantial discount against the delivered item that I was unhappy with ( rather than to collect and replace).
My view is that identifying the cause will not change the most cost effective remedy of converting to a pumped system.
With respect to Telford, I have always found them very responsive and quick to offer a substantial discount against the delivered item that I was unhappy with ( rather than to collect and replace).
Came across this re friction loss in corrugated pipes, the DN25 is nearest to the one above, a flow rate of 10LPM = 0.02M/M loss so the 5.8 coil should require 0.116M head. If the flow rate was 2 LPM (due to Thermosyphon) then the coil loss would only be 0.00464M and even allowing for the added pipeline losses there should be no reason IMO why the higher corrugated pipe losses should be a problem.
I read somewhere that clearing air from corrugated pipes requires a velocity of > 0.5 mps which will never be achieved with a gravity flow and this bore piping so hopefully your air purging etc will get rid of any air as the flow rate has to build from zero in this gravity system and any trapped air won't help.
Technical Information | Easyflex
www.easyflex.co.za
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Came across this re friction loss in corrugated pipes, the DN25 is nearest to the one above, a flow rate of 10LPM = 0.02M/M loss so the 5.8 coil should require 0.116M head. If the flow rate was 2 LPM (due to Thermosyphon) then the coil loss would only be 0.00464M and even allowing for the added pipeline losses there should be no reason IMO why the higher corrugated pipe losses should be a problem.
I read somewhere that clearing air from corrugated pipes requires a velocity of > 0.5 mps which will never be achieved with a gravity flow and this bore piping so hopefully your air purging etc will get rid of any air as the flow rate has to build from zero in this gravity system and any trapped air won't help.
Technical Information | Easyflex
It would be helpful if you could find the reference for "clearing air from corrugated pipes requires a velocity of > 0.5 mps" especially as Telford advertise :
"Telford Stainless Vented Cylinders
Suitable replacement for copper vented
Telford Copper & Stainless Cylinders Ltd offer a stainless steel version of the conventional open-vented cylinder, traditionally made from copper. Made in the same production line and from the same material as our Unvented range, we can offer a cost effective alternative to copper vented cylinders that are manufactured to the same high standards as our unvented range."
The above words appear in their earlier publications but at the time of writing it is at the top of page 7 of the first download at: Telford Copper & Stainless Cylinders Brochure | Tristor, Tornado & Tempest Installation Guides - https://www.telford-group.com/downloads/general-downloads/
Before I placed my order I wrote to Telford and said: "I wish to replace a 20 year old 1200x450 Hercal hot water cylinder with the minimum of plumbing alterations." My initial email to Telford included a full specification and drawing of the cylinder I wished to replace.
They did warn me that most pipe connections would be in different locations to the Hercal but they did not warn me that they would supply a corrugated coil which would not self-clear air locks.
The delivered cylinder came with a 5 year printed guarantee and despite several protests they have still not replaced it with their widely advertised 10 year guarantee.
It is unfortunate that an established, well respected company, allowed this order to go so badly wrong and have done little, so far, to put it right.
Sorry Neville, but I just can't locate that link just now but it certainly stated a minimum velocity which I think was 0.5 mps so common sense would indicate that corrugated piping isn't compatible with large bore piping and low flow rates which are common to gravity flow systems, IMO.
Its strange that Telford can't/won't provide "evidence" of a cylinder similar to yours with a corrugated coil running on gravity circulation.
Its strange that Telford can't/won't provide "evidence" of a cylinder similar to yours with a corrugated coil running on gravity circulation.
I have not asked Telford for this evidence. Mainly because some while ago I had unhelpful email exchanges with a senior member of the company so wish to be very sure of my grounds before I go back to him.
From information supplied here I am hopeful that I will be able to get it working but it may first need mains reverse flushing to remove air locks.
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Thanks for the useful information. Nice looking cylinders at joule.ie/knowledge-centre but they don't appear to do vented although this may not alter the gravity circulation criteria. Unvented is probably less likely to suck in air during normal use.
One of our people fitted a Replacement Telford Indirect Vented cylinder (type G 9E) today in a three storey property in Oxford. This was a pumped system. However, looking at the literature and the instructions et al that came with the cylinder (delivered to us direct by Telford) - it is fitted with a 28mm inside diameter coil. From the chart ( which sets out the full standard vented Telford range (models 0 to 14 plus 9E)) in the instructions, There are only two models in the standard Telford range the 0 and 1 (96litre and 72 litre respectively) that are fitted with a 22mm inside diameter coil. It is stated in the notes that these cylinders are for pumped primary’s only.
All the cylinders in the Telford range for gravity circulation are shown as having either 28mm or 35mm id coils
All the cylinders in the Telford range for gravity circulation are shown as having either 28mm or 35mm id coils
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No, copy appended below
Attachments
7. Bathoom radiator loop providing a low impedance path in parallel with the cylinder coil.
Did you change the lockshield setting on that radiator at some point? If so, you might have left it too open.
Personally, I'd have fitted a circulating pump about a year ago. It doesn't take much to stop gravity circulation working and diagnosing the cause is often a waste of time because the remedy is mostly likely to be 'fit a circulating pump...' anyway.
I am afraid I could not read your attachment. I have looked for the equivalent page on Telford's site and found the attached. It appears that the table is for copper and not stainless. I could see no mention of "internal diameter". I suspect 22mm and 28mm refer to the compression fitting sizes and not the pipe diameter. If you do have a readable page specifying an internal diameter of 28mm I would be interested to see it.
My problem relates to the cylinder supplied to me but nevertheless it would be interesting to see if there has been a move to larger pipe sizes.
I suspect that corrugated is the cheaper solution for stainless as a very thin wall will withstand quite high pressures and it is easily made into a coil. A plain copper coil is an established technology and may still be relatively inexpensive.
[automerge]1590231834[/automerge]
The coil gets zero heat with all settings of bathroom radiator valves including completely closed.
Gravity circulation has never been a problem for me with older central heating systems. It had worked, without any difficulty, in this property for about 50 years until I changed the traditional Hercal copper cylinder to a Telford stainless cylinder.
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Have the horizontal runs been checked after the new install? Is it possible the horizontal run could have been disturbed and pushed down under the floor causing a drop in the pipework rather than a steady rise. As I think other's have said the distance the gravity circs are run Horizontally seems quite large - however if it's worked for 50 years before must be OK
(And Bathroom rad works)
I had a very similar issue with my in Laws log burner and heat sink rad that was fitted by a previous installer. The rad would always work however the coil in the cylinder wouldn't - I concluded before ripping the thing out was that the circs to the cylinder didn't have great enough horizontal gains as the pipework was clear.
I've replaced old gravity cylinders with cylinders that are meant to be fully pumped before now (Due to what was needed and future upgrades coming) and never had any issues with them circulating on gravity systems.
What was the issue with the old cylinder? Did it leak or was a leak developed on the coil and CH & HW water was mixing?
(And Bathroom rad works)
I had a very similar issue with my in Laws log burner and heat sink rad that was fitted by a previous installer. The rad would always work however the coil in the cylinder wouldn't - I concluded before ripping the thing out was that the circs to the cylinder didn't have great enough horizontal gains as the pipework was clear.
I've replaced old gravity cylinders with cylinders that are meant to be fully pumped before now (Due to what was needed and future upgrades coming) and never had any issues with them circulating on gravity systems.
What was the issue with the old cylinder? Did it leak or was a leak developed on the coil and CH & HW water was mixing?
From the calculations in this thread it appears very unlikely that there is insufficient pressure around the circuit to promote gravity circulation. However removal of air locks is another matter. I am not aware of the pipes under the floor having moved very much but there could be less slope than before. The only practical way to examine this is to remove a portion of kitchen ceiling which I am reluctant to do unless all else fails.
Earlier cylinders only lasted about ten years but this last one was over 20 years old. They were all Hercal but the latest one had a sacrificial anode. The early ones leaked between primary and secondary but the last one developed a small hole at a weak point near the blanked immersion heater opening. This had been patched several times. Initially by Araldite and more recently by solder.
You can, I've done it a few times.
If you haven't already, you could try saving it on a drive, then click on the file name to attach it.
I would be grateful if you could post the PDF to this site.
Thanks for the PDF. Whilst you may be correct about the internal diameter I am unable to find any reference to 'internal diameter'. In the attached enlarged chart I can only see a column called 'Size of Primary Heater' which I am inclined to think are compression fitting sizes.
Attachments
“Size of the primary heater” is the Internal diameter of the coil in mm.
The connections on Telford vented cylinders are normally all the same - G1 which has a Nominal Bore of just under 30mm irrespective of the internal coil internal diameter.
in essence, you cannot determine the internal coil diameter from the external connection. Unless of course you have long thin fingers!
The external fittings are shown in the last two columns of the chart that you have posted
The connections on Telford vented cylinders are normally all the same - G1 which has a Nominal Bore of just under 30mm irrespective of the internal coil internal diameter.
in essence, you cannot determine the internal coil diameter from the external connection. Unless of course you have long thin fingers!
The external fittings are shown in the last two columns of the chart that you have posted
My understanding is that G is the German/ISO designation equivalent to BSPP. These were specified for thick steel gas pipes and so tend to be a size larger than copper. G1 was originally for a pipe with a 1 inch internal diameter.
Whilst I am not saying you are wrong, I continue to have two problems with this chart:
1 - it is for copper cylinders and not stainless
2 - internal coil diameter is not clearly stated.
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Not yet - too many other things going on.
A member of my family is having the same problem as you. Gravity fed boiler.28mm sloping pipe from boiler to cylinder. She had no heating too. The boiler had not been on all summer and when she recently tried it, had no hot water or heating. The boiler was installed in 1977. I found that the radiators were full of sludge and that this had caused the heating pump to jam. However, there are still no hot water. The 28mm flow pipe was stone cold. I then flushed the heating water for 5 mins with the drain connection on the base of the Ideal Vulcan boiler where there is a drain cock. Only 5 mins of gravity fushing and the flow pipe immediately got hot. I left because it was getting late and later found that she still had no hot water. I am going round to power flush the system. I think there is a build up of sludge at the base of the flow pipe. Will be carrying the flush out next week. I think a power flush with cleaner will do the trick removing any air lock and sludge ( just the risk of a leak but at least the problem will hopefully be cured ).
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