GeoffT
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| posted on 25/11/10 at 10:42 AM |
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O/T Another one for the plumbers amongst us...
Just moved into a single story home (no loft) with an old fashioned indirect heating system. Due to space restrictions there is no feed and expansion
tank, just the normal cold water storage tank supplying the main body of the indirect cylinder and thence the hot water taps.
Which begs the question - how is the feed and expansion catered for in the primary circuit? Answer is, the open vent simply vents to the outside
world, and the feed is from....the cold water storage tank! This connecting pipe has a sevice valve but no non return valve.
Surely this cannot be permissable, as it allows a direct connection between the filthy crap that passes for water in the rads to the hot water from
the taps? The rads badly need a flush and some inhibitor but I'm not keen on doing this if the inhibitor is likely to contaminate the hot water
supply.
I was thinking that a quick fix solution might be to add a non return valve in the feed line from the storage tank to the primary but that would
prevent any expansion back up the pipe, although the open vent would still hopefully cope with this?
I'm planning in the future to rip all this out and fit a combi system, but in the meantime I'd welcome any comments on the way this is
currently plumbed and whether my quick fix is ok. Would also advise any visitors to decline the offer of a cuppa.....
Geoff.
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t16turbotone
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| posted on 25/11/10 at 06:01 PM |
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There is usually a 'coil' in the hot water cylinder which provides seperation between the two circuits, u2u me if you need further
explanation
tony
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bob tatt
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| posted on 25/11/10 at 06:57 PM |
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sounds to me like you have what is called a primatic cylinder where the seperation is achieved by a loop in the top of the primart coil which has a
air pocket in it. Dont start fitting non return valves as the system needs to be able to expand , think of it this way if the boiler dstat fails and
starts to boil the water what will happen if uts route to atmosphere is blocked by a non return valve.
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GeoffT
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| posted on 25/11/10 at 07:28 PM |
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quote:
sounds to me like you have what is called a primatic cylinder where the seperation is achieved by a loop in the top of the primart coil which has a
air pocket in it. Dont start fitting non return valves as the system needs to be able to expand , think of it this way if the boiler dstat fails and
starts to boil the water what will happen if uts route to atmosphere is blocked by a non return valve.
It looks like a completely normal indirect hot water cylinder, I can't see any evidence of it being a primatic cylinder, though have to admit
I've not seen one of those before, so don't know exactly what it would look like. If you imagine a normal indirect cylinder with the two
pipes into the coil, the cold feed into the bottom and the hot pipe from the top - that's what I've got.
My thinking is that although the check valve would stop any expansion up the feed pipe from the cold storage tank, the open vent from the primary
would still be open and would cope with any expansion. Not normal I know, but I'm just looking for a temporary fix to some very odd
plumbing.....!
Geoff.
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adam1985
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| posted on 25/11/10 at 08:32 PM |
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Sounds to me like its a direct cylinder ( no coil) this is more common than you think only bad thing is you bath water has done a few laps around the
rads
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GeoffT
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| posted on 25/11/10 at 09:06 PM |
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quote:
Sounds to me like its a direct cylinder ( no coil) this is more common than you think only bad thing is you bath water has done a few laps around the
rads
How can it be a direct cylinder when it has a coil for a separate primary circuit?
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adam1985
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| posted on 26/11/10 at 11:44 PM |
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How do you know it has a coil
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bob tatt
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| posted on 27/11/10 at 04:52 PM |
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how many header tanks are in the loft if there is one large one but no smaller one then its primatic
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GeoffT
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| posted on 27/11/10 at 06:12 PM |
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quote:
how many header tanks are in the loft if there is one large one but no smaller one then its primatic
.......there's no loft, I've just got the large cold water tank in the top of a cupboard, there's no F&E tank.
I beginning to think you must be right about this being a primatic cylinder, I can't imagine any plumber would use a standard indirect cylinder
with the piping layout I've got. I'm struggling though to determine that it is a primatic jobbie, it would appear that they look the same
as a normal indirect cylinder externally?
Searching round the back of the cylinder with a mirror, I've found a label which identifies it as a CenterCyl HE 85. Looking on the net plenty
of references to it as an indirect cylinder, but I can't find the word 'primatic' levelled at it anywhere. Do you reckon it is?
You live and learn though, I'd never heard of a primatic system before this thread.....
Geoff.
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bob tatt
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| posted on 28/11/10 at 10:11 AM |
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had a quick dig and the cylinder is quite recent and from plumbcenter, its not primatic but is indirect.
ant chance you can do a line drawing of the layout and i should be able to tell whats what. Has the heating system been pressurised at nay time or is
it open vent and are you sure the vent and feeed to the heating circuit is still connected adn not capped off out of site somewhere.
hope this helps rob
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GeoffT
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| posted on 28/11/10 at 11:26 AM |
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Rob,
The system doesn't appear to be pressurised, the open vent from the primary loop is in fact open. It is routed via a cobbled syphon break (15mm
pipe dropping into an open 22mm pipe section) which then routes to the outside.
It's looking like the system was installed as primatic, and sometime recently the cylinder has been replaced. I'm guessing that whoever
did the job didn't realise (or care...) that the original was primatic, and fitted a normal indirect cylinder.
I'll try a do line drawing later, but if you imagine it's a normal indirect layout, but the feed pipe to the primary loop is from the cold
storage tank (yes, the same one that supplies the hot taps...) instead of an F&E tank - that's what I've got.
It's probably all going to be ripped out and replaced with a combi in a couple of years or so, in the meantime I'm really just trying to
make the installation reasonably safe and to be able to run it with some inhibitor, it's appears to be corroding well at the moment judging by
the colour of the rad water. There's no viable way to fit a F&E tank, I was thinking of maybe sealing the primary and using a pressure
vessel with a filling loop, trouble is I'm not sure if the boiler is suitable for pressurised operation. It's an old Trianco TRO 12/14 oil
fired effort, can't seem to find much info on this.
Anyway, many thanks to yourself and all the other posters for the help, I seem to be finally working out what I've got here....
Geoff
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geoff shep
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| posted on 28/11/10 at 02:10 PM |
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Here a few diagrams from a google image search:
http://www.causewayheating.co.uk/whichboiler.cfm
In each system, water can expand back up the inlet pipes or can overflow back into the header tank. Each header tank is topped up by mains cold water
via a ballcock. Each tank should have an overflow, usually out through the roof.
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bob tatt
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| posted on 28/11/10 at 02:51 PM |
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i dont think you will be able to add inhibitor, i will try to explain why as best i can. If you are to fit a non return valve to the primary heating
feed this could cause problems as most of the expansion is taken up into the feed and expansion tank not over the vent. The vent is there as an
excape route for the system to aid filling by letting air out and if the system over heats to allow the water to pump over. So imagine you fit the non
return on the feed this means that the normal expansion will go over the vent and go externally, now everytime this happens you are adding new water
to the system thus removing inhibitor.
To be totally honest if its all coming out soon id leave well alone and it could take years for the system to pin hole and block up, when it comes
time to replace the system run some good cleanser through it and flush, or alternativaly pull the lot out and start again its not as big a job as you
think.
And your right by the sounds of it the last installer has not realised it was a primatic taken the job on then bodged it with the external vent.
If you have any questions please feel free to contact me and i will try my best to help.
rob
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GeoffT
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| posted on 28/11/10 at 05:55 PM |
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Thanks guys, seems my options are pretty limited, other than rip it out and start again.
I've got an idea rolling round my head of temporarily using a very small F&E that I could squeeze in the available space. This would have a
feed to primary and overflow only (no room for a ballcock) and then manually top it up when necessary. Obvious implications if you forget to top it up
though.
Realistically, I suppose I'll just have to live with it for the time being. Never mind, if nothing else I've learnt about the universally
unloved primatic cylinder...
Geoff.
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