Convert corrugated grain silo to water tank

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Convert corrugated grain silo to water tank

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kGarden

Joined: 01 Dec 2014
Posts: 178
Location: Suffolk, UK

Posted: Thu Dec 04, 14 3:17 pm Post subject: Convert corrugated grain silo to water tank

I am blissfully assuming this is a POP, but best I ask in case anyone has experience, advice or warnings.

Chap down the road has an old grain silo spare. Its been cut into two, bottom and top half. The top has a cone-shaped lid, which would keep the crud out and I favour that, especially as the bottom half has an inspection door which I suspect will be much harder to strengthen etc. to contain a Buytl liner.

Bit hard to tell, for me, but I suppose it is possible that the bottom half is a heavier gauge of sheeting?

I see new corrugated circles sold, with Buytl liners, for rain water storage so I am assuming I can just chuck a liner in it and away I go

Silo is 18' diameter, assuming 2M-ish tall I make that 47,000L / 10,000 Gallons. In the driest 18 months over the last 10 years we would have needed 100-150 KL more water than the actual rainfall (assuming we collected 100%), (the metered water to the house would have matched that usage rate).

We have replaced original cesspit with a digester. Downpipes from house and some land drains now re-routed to the old cesspit - I am hoping that Chamber #1 will let all the silt settle out, so that the water in Chamber #2 should be clean enough to use for irrigation. Mostly we irrigating using leaky hose, I figure if I decide to use Drip Irrigation nozzles in future I'll need a fine filter.

Maybe I also need a Wisy vortex filter on the inlet?

Water from the outlet of the digester has valves to divert it to either the ditch or into old cesspit. I prefer rainwater for my plants, but if we run low in Summer I could make use of outfall from digester.

I was planning to use a submersible pump in cesspit Chamber #2 to lift the water into the new tank, and then a pump to provide pressure to the irrigation pipes (not sure of the correct term I read things like "2-stage" and see that there is a pressure vessel attached which brings the pump on automatically when a tap is opened and the pressure falls - dunno if I need that, or just a timer?

My plan was to use a water metering device, rather than a timer, to auto-stop the irrigation (so presumably need a pump that will shut off when that valve closes, rather than an electrical timer).

dpack

Joined: 02 Jul 2005
Posts: 45514
Location: yes

Posted: Thu Dec 04, 14 3:55 pm Post subject:

i have no direct experience of what you are considering

however my experience of structures and of water makes me think that if it will be deep it needs to be strong

ie big and shallow can be flimsy,big and deep must be strong

and water is denser than grain as well as being more "floppy" so a few metres of water will exert more sideways force than a few metres of grain in a big tube

could you bury it in a hole to provide inwards side force ?

kGarden

Joined: 01 Dec 2014
Posts: 178
Location: Suffolk, UK

Posted: Thu Dec 04, 14 5:11 pm Post subject:

dpack wrote:

could you bury it in a hole to provide inwards side force ?

It would be under some trees, so might damage their roots a bit when making the hole, but its a good idea thanks. I'll give some thought to an alternatively location where a hole would not trouble any plants.

Perhaps the ones sold for water storage are a thicker gauge, but they are readily available at 18' diameter up to 3M (although 3M seems to be the max height offered, regardless of diameter)

e.g. https://www.easy-irrigation.co.uk/index.php?main_page=product_info&cPath=73_101&products_id=825

Behemoth

Joined: 01 Dec 2004
Posts: 19023
Location: Leeds

Posted: Thu Dec 04, 14 5:25 pm Post subject:
If full you would have 47 tons of water trying to get out. I'd get an engineers advice.

onemanband

Joined: 26 Dec 2010
Posts: 1473
Location: NCA90

Posted: Thu Dec 04, 14 8:44 pm Post subject:

If you go about it right I think it'll work - although I have no experience of grain silos or water tanks.

Think about inflatable pools - they rely on being perfectly round - lean too hard and they collapse, likewise if they are put on sloping ground.
The tensile strength of the material in an inflatable pool is a fraction of the tensile strength of sheet steel.
So as long as the metal sheets are properly bolted to each other to form a completely bolted circle(as opposed to screwed to the frame), your silo is fairly round, with no major creases or dents, and is level then I see no problem.
Just bolt sheets over access door.

dpack

Joined: 02 Jul 2005
Posts: 45514
Location: yes

Posted: Fri Dec 05, 14 12:45 am Post subject:
i recon the 47 tons thing is quite a challenge for any structure

dpack

Joined: 02 Jul 2005
Posts: 45514
Location: yes

Posted: Fri Dec 05, 14 12:46 am Post subject:
big hole ,lorry tarp ,lid ,pump that leaves the rings as pig arks or whatever

Mistress Rose

Joined: 21 Jul 2011
Posts: 15598

Posted: Fri Dec 05, 14 7:52 am Post subject:

A circular structure is always stronger than a straight sided one, but the weak point is how the cladding is attached. If the frame is on the outside, the cladding is being pushed against if and this will mean the frame strength is the critical point. If the cladding is screwed to an internal frame, the attachment is the weak point. If you can bury it, the soil round the outside will keep it stable as Dpack says, and if it fails you will get a water spout rather than a tidal wave.

If you have any neighbours down hill from you, make sure you won't wash them away if it fails.

kGarden

Joined: 01 Dec 2014
Posts: 178
Location: Suffolk, UK

Posted: Fri Dec 05, 14 7:52 am Post subject:

onemanband wrote:

Think about inflatable pools - they rely on being perfectly round - lean too hard and they collapse, likewise if they are put on sloping ground.
The tensile strength of the material in an inflatable pool is a fraction of the tensile strength of sheet steel.

Makes sense, thanks. A good part of the force from the 47 tonnes must be downwards, perhaps that is why 3M is the max height I see, outward pressure is perhaps the same, at 3M, regardless of the diameter / volume

dpack wrote:

big hole ,lorry tarp ,lid ,pump

Hmmm ... I can dig a hole cheaper than I can buy (new) a corrugated water store, yet they are popular and commonly used (not sure I have seen any/many small pond water stores? - until we get up to decent sized farm reservoirs)

Is there an issue with the ground water pressure when I pump out the hole-in-ground? Swimming pools have an adjacent vertical drain to be pumped out in the event that the pool itself is to be emptied. I suppose a liner would just float on any ground water that pushed in under it, when water level was low, perhaps that is not a bad thing?

Also wonder if the irrigation pump is going to be less trouble fed under some pressure, rather than relying on always being primed when the water level is below it?

Falstaff

Joined: 27 May 2009
Posts: 1014

Posted: Fri Dec 05, 14 8:13 am Post subject:

kGarden wrote:

............... outward pressure is perhaps the same, at 3M, regardless of the diameter / volume.............

Absolutely right. The outward pressure exerted by the 47 tonnes is dependent on two variables - depth and atmospheric pressure

Atmospheric pressure can be considered as a constant in this case and will support a column of water 10 metres high. So 3m is a little less than a third of this and since atmospheric pressure is a little less than 15 lb / sq inch the outward pressure at the bottom of the tank will be a little less than 5 lb per square inch.

Doesn't sound much - but when you consider it over a slightly larger area, that becomes 720 lb per sq foot or just about 3 tons per square yard

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