Your thoughts...twin fluidmasters in the same cistern...

[AV1]

Picking up on the a previous design idea, what's your thoughts.....on fitting 2 fluidmasters into the same cistern, the mains, fitted with a twin check and isolation valve for when the second valve fitted for harvested water  fails due to drought/frozen.
Adrian

[solar_cambridge]

You can't put a mains fed valve into a tank containing rainwater in the way you suggest. There must be an air gap  -a double check valve isnt enough.  You can achieve it by cutting a 'weir' into the side of the tank, then standing the bigger tank onto a trough which is drained to outside. Then if the rainwater gets too high it will never reach the bottom entry of the mains valve.

Hope that makes sense! You have to consider the worst case scenario which would cause rainwater to feed back into your drinking water! Thats why you cant just put two ballvalves into a toilet cistern!

[mespilus]

Would a non -return valave in the mains supply to the cistern
do an adequate job to prevent rain water feeding back into
the drinking water?

[andyparry]

Hi mespilus,

A double check valve only gives back pressure and back siphonage protection to fluid category 3 - fluids which represent a slight health risk, such as water from wash basins, washing machines and showers.

Rainwater is deemed to be category 5 for both back pressure and back siphonage; a fluid which represents a significant health risk.

As solar_cambridge pointed out, one solution is to incorporate a weir into the cistern were the two waters meet, with a 20mm air gap, or twice the inlet bore diameter (whichever is the greater). Another possible solution is to have this air gap above the cistern.

andy

[mespilus]

Thanks for the clarification.

Are you saying if the rain water-fed Fluidmaster,
and overflow outlet are set so its maximum water level
is at least 20mm or twice incoming pipe diameter
below the outlet from the mains-fed Fluidmaster,

that would be OK.

Sorry to ask a dense question, but I am finding it hard to visualise the 'weir' concept.

[solar_cambridge]

Sorry to ask a dense question, but I am finding it hard to visualise the 'weir' concept.

Imagine you are standing on a bridge over a weir... Your feet can never get wet because the level of the water will never reach the bridge (hopefully). 

Your cold water mains outlet must be in a similar location to your feet on the bridge! In other words, no matter how high the water in the tank gets, it will always flood out of the weir therefore never ever able to contaminate your drinking water!

There is a calculation to work out the size you need to cut out for the weir. If you went for a letter box size opening that should be more than sufficient!

[andyparry]

Hi mespilus,

A Type AA air gap is where the outlet for the valve is above cistern top so you don't actually need a warning pipe outlet (aka overflow) because the water will flow over the cistern sides. The valve will need to be supported by some other means because it is held higher than the cistern.

For a Type AB air gap, using a weir, you can use the cistern sides to support the valve.

I can email you some pic's from my reg's hand book if you like, just let me know.

Regards

Andy P

[mespilus]

Hi mespilus,
I can email you some pic's from my reg's hand book if you like, just let me know.

Regards

Andy P

I will take you up on that kind offer: resins.man at googlemail.com

with the obvious correction will find me.

Thanks in advance.

[andyparry]

Hi Mespilus,

Sent you an email with 4 PDf documents which I hope will be use to you. Let me know if you don't get them or need to know more

Regards

Andy Parry

[guydewdney]

If rainwater is 'a significant health risk' - then why are we allowed out in the rain? 

[AV1]

Thanks for replies....nice thought on going out in the rain LOL.
OK then it's a top up system of the external tank, that has to be done manually.
Adrian

[plumbskill]

If I understand correctly... you just need to use mains water when your rain water tanks are dry. I would have thought that by using a combi filling loop that has a double check valve fitted, that it would be legal, as long as the "temporary loop" is disconnected when not being used.
I would have thought that there would be more of a health risk if central heating water were to get into the mains, thats why, temporary filling loops are a requirement.

[andyparry]

Hi All,

It's not the rainwater that is the problem, it's all the 'little bugs' - parasites and all that it picks up as it drains down your roof then sits in a barrel.

If you filled the external tank manually by standing over it with a hose pipe, then that would be OK (provided you maintained an air gap and did not drop the hose pipe into the rainwater)

You have to remember that parasites and bacteria are far deadlier than the chemicals in central heating systems - these chemicals are diluted out and they do not multiply - parasites and bacteria DO when they invade their host - YOU.

A combi-filling loop and double check valve is OK for lower class category fluids, but stored rainwater is a cat 5 fluid; the highest and this type of mechanical backflow is not effective.

I know it's a bummer all this regulation stuff, but it's to protect the mains water that other people use as well. We do not want to appear on 'Rogue Environmentalist' do we.

Right, I'm putting my Policeman's hat away now for good - no more nagging 

Regards

Andy

[guydewdney]

But - mains pressure is (virtually) always higher than some poxy tank in an attic - isnt it? Therefore if there were to be a hole from mains to tank water - its would flow that way - taking any ikky bugs with it?

If not - surely a simple air gap (like a bog filling valve, 1/2" above the water) would prevent any ikky bugs flying up, and through a closed valve, and into the slightly chlorinated water....

Not 'avin' a go - just wondering what century the regs were written in?

[Imintheshed]

Hi Mespilus and / or Andy Parry,
Any chance you could forward a copy of those PDF docs to me as well? I've tried Googling the weir system you refer to but can't find it and am struggling to visualise how the tanks are set up. richconnah at yahoo.com please!!
Cheers
Rich