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Author Topic: Quick tool-less changeover between rainwater and mains for shower (Hot and cold)  (Read 2845 times)
al_uk
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« on: December 08, 2014, 11:20:41 PM »

My 2nd hot water system has been in for about 3 years now and is working well. This is a vented cylinder with a header tank supplied by rainwater only. It is heated by the heating circuit of the combi boiler and also a home made Immersun type device. This feed via a shower pump to one of the showers. The DHW section of the combi feeds the rest of the hot water in the house with mains water.

I want to be able to switch this shower between rainwater and mains water easily. This is so that if guests want to use mains water then they can, and also if there is a problem with the rainwater system we can easily switch over.

I would like to stay reasonably legal as regards the water byelaws and avoid potential contamination of the mains water from rainwater. So I can't just join the 2 systems together via a couple of lever valves.

I could use a filling loop flexible changeover for the cold water fill to the header tank, where I can connect the other end of the flexible loop to either the rainwater or the mains water connector. However that means that there is a header tank and cylinder full of rainwater before the mains water comes through, so it isn't an instant changeover.

So I'm looking for ideas for a changeover arrangement I could put on the hot and cold feeds to the shower. It needs to be full bore 15mm or 22mm.
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guydewdney
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« Reply #1 on: December 08, 2014, 11:56:04 PM »

Can't you use double check valves to be llegal?

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al_uk
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« Reply #2 on: December 09, 2014, 12:01:53 AM »

My understanding is that there has to be an air gap, and that double check valves aren't enough.
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dhaslam
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« Reply #3 on: December 09, 2014, 12:50:48 AM »

I have a  separate  attic water  tank for  rainwater although it only feeds the hot water.    If the water supply from the rainwater tanks runs low  there is a  mains feed lower down in the attic tank which takes over automatically.   The mains feed  goes downwards so   the water cannot flow back into the mains but in retrospect I should have filled from the  other water tank  with a larger pipe because the mains flow is too slow.   It is quite hard to fit a lower ballcock because  there is  too much flotation in  fully submerged ballcock  and the  feed has  to be above  water so the arm has to be extended downward. 
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oliver90owner
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« Reply #4 on: December 09, 2014, 07:19:19 AM »

If using the same header tank it is a simple matter of adding a(nother) ball valve which only opens the mains inlet at a reduced water level (as dhaslam).  The overflow outlet must, of course,  be below the inlet so as to maintain the air gap.  Removing/turning off the rainwater supply will effect the change over, given time, as there is always going to be at least the cylinder full of rainwater.
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Ivan
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« Reply #5 on: December 13, 2014, 02:14:54 AM »

I think the overflow has to be relatively big too - to make sure that it will overflow fast enough to prevent the air gap diminishing.
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