Another pipe size question

[fatbob]

Hi,

I'm hoping someone might be able to help me understand a bit better how pipe sizes can affect water distribution, in my case around the garden in a gravity based system.

At the moment I collect water from the back of the house in water butts linked by 25mm pipe to an IBC at the bottom of the garden.  Now that we have had some rain at last and the tanks are approaching full, the last heavy shower caused one of the water butts to overflow with the large volume of rain that came down.  There was still space in the IBC to take the water, but the problem was that there was not a quick enough flow through the linking pipe to equalise the levels before the collector butt started to overflow.  The collector butt is 100L, with its overflow about 10cm higher than the IBC overflow.  This was to allow some 'give' in the collector butt when raining to allow time for the water to level out between the butt and IBC.

Currently there is a 25mm pipe linking to the IBC, I'm wondering whether extending the pipework to create a water 'ring main' around the garden (ie 2 x 25mm pipe runs) would help.  The run from house to IBC is about 30m.

One thing I really don't know is how the connections to the butt and IBC would affect water flow as they are via standard 3/4 inch waterbutt connectors - would those be the absolute limiting factors in the water flow regardless of the linking pipe diameter ? ie would it make any difference adding an extra pipe or a fatter pipe or would I have to upgrade the size of the tank connectors also ?  Probably a daft question but I'm sure you'll be kind 

An obvious solution to the overflow problem would be raising the collector butt a bit higher to give a little more leeway in heavy rain, which I'll probably do anyway, but this got me thinking about water flows vs pipe sizes vs distances etc which in all honesty has got me rather baffled !  If anyone can help improve my understanding, I'd be very grateful.

Thanks,  Bob.

[desperate]

Yo fatbob

How about linking the butts at the bottom creating one big store, this would give more time for the water to travel to the bottom of the garden, the 3/4 tank connector is going to be a fairly tight restriction to the flow, but the pipe length and friction will have an effect as well. There is a pipe sizing calculator somewhere on this site, if you search it out, that may be of some help. If you use 2 lengths of pipe it will increase the flow rate a bit, and especially if you have 2 tank connectors. I think it will be cheaper though to get some larger tank connectors and use 1 length.

Desperate

[knighty]

check all the connections and make sure they're ok... no super restrictive ones there....

and then use your house to push some water through the pipe as quick as possible.... my bet is there's some sediment/junk in the pipe slowing it down...

even in heavy rain, there's not normally that much water coming down from the roof ?
(only when it's really heavy!)

[desperate]

Knighty said:-
even in heavy rain, there's not normally that much water coming down from the roof ?
(only when it's really heavy)

not so sure about that mate, 

If you are collecting from 50m2 roof area,ie normal semi type size, then 20mm/hr is not that unusual in the uk for short bursts, you are looking at 1000l/hr at the butt which will need a fair bit of pipework to shift. Try filling a 3gallon bucket from the kitchen tap in a minute to give you some idea of the rate.


Desperate

[Philip R]

Hi fatbob, I like your scheme to collect the rain water.
Your 25mm pipe is probably blocked with some roof detritus, restricting the flow. Also as the IBC approaches full, the differential pressure of the butt water to the IBC down the long length of 25mm pipe is going to drive no more than a mouse piddle flow rate down the pipe, hence the overflowing butts. I suggest:

1. Pump from the butts to the IBC using a submersible type pump and flexible hose. Or
2. Augmenting / replacing the 25mm (PE?? pipe) with larger diameter pipe, have a look at the "pipestock" website for some ideas. ( I will be lambasted for pasting in the webpage). Or Ebay
3 Another idea would be to use PVC waste pipe, need to think how to couple it to the butts,  it is relatively cheap compared to PE pipe and moving the water at low pressure. 

Regards, PhilipR.

[fatbob]

Thanks guys some good suggestions there for me to work on.

I'm fairly confident that the pipe run is crud free, but there again you never can tell and it's been in use for a couple of years now.  Now that I have a good head of water in the tanks to play with, I will flush through just to make sure.  I have a bespoke 20 denier filtration system on the downpipes (ie mother in laws tights) which catches the larger chunks of crud.

Desperate, your info on rainfall rates is very useful, my rough guess is that this downpipe drains about 30m2 of roof area.  Typical rainfall patterns in the summer where I am in the south UK is that there's no rain for weeks and then we get a months worth in an hour or two, so the setup needs to cope with large amounts of water in a short space of time.  I'm going to look at a second pipe run with an extra tank connector to help increase flow rates at the IBC.  The butts/IBC are already linked at the bottom to create a big store as suggested.  I think the main problem is the size of the 100L collector butt, I have another downpipe which empties into an interlinked 700L collector/storage butt which coped fine.  I've looked at the pipe sizing calculators, but my O level maths is just not up to it !

PhilipR, you're right, once the levels are quite high in the tanks, the differential is so small the flow rates between house and the IBC are fairly low.  I'm thinking to raise the collector butt higher will help increase flow rates and give the system more time to level out in heavy rain.  A pump and float switch arrangement to help shift the water to the IBC quickly in overflow situations would help for sure.  I'm fairly committed to 25mm pipe as upgrading sizes now would be quite a pain as everything is already plumbed using it, but I could add an extra pipe run fairly easily.  I'm using flexible pond pipe rather than PE, simply for cheapness and ease of plumbing in connections and outlets as it fits very well onto standard 22mm plumbing fittings.  It's not the toughest in the world but has lasted well so far (touch wood).

I will continue to experiment (play) with the setup to see how it can be improved.  The missus always laughs at me as everytime it rains (especially heavy rain) I'm wandering around the garden with an umbrella checking flows and levels etc.  It keeps me amused if nothing else 

Cheers,  Bob.

[DonL]

Hi Bob,
The driving force for the water flow is the difference in height between the water level in the butt and the water level in the IBC; so when the IBC is empty you have a big difference in height and the flow produced will be greater and may handle even very heavy rain without overflowing.
It may be only when the IBC is nearly full that the problem occurs and maybe that's not worth worrying about as it may be only a marginal difference in the amount you capture over all.
Don

[fatbob]

Hi Don,

Yes you're right, I guess a little overflow water when the IBC is nearly full probably won't be a big deal in the grand scheme of things.  I still have two more downpipes to plumb in, so once all are collecting I can be a little more relaxed about losses.

I do have plans underway however to utilise a stack of two IBC's and pump from the bottom one to the top one to use as an additional reservoir for dryer spells.  This will rely on getting water to the bottom IBC in a fairly efficient way as I plan to set the pump to activate at that 'near full' level.  As always though, grand plans are great, but it's getting them working in real life that presents the challenge.  I shall continue to play and see how I get on !

Cheers, Bob.

[knighty]

it you used 2 floats instead of one you could have.....


float in bottom of bottom ibc, to cut off pump if bottom ibc is empty

float in top of top ibc, to cut off pump if it is full


that way the level in the bottom ibc would always be as low as possible, giving you the best flow rate possible ?

[fatbob]

Hi Knighty,

You have got me thinking there - why didn't I think of that ?  Damn !  I could use the upper IBC as the main tank for water delivery around the garden, and maintain it as full with a pump.  The only problem would be that all the collector butts, outlets, taps etc already share the 'lower' pipe circuit, so it would involve a fair bit of replumbing and an additional pipe run around the garden to separate the outlets and inlets.  It would be very good to have a steady 1m+ head though, and as you suggest would keep the lower IBC as empty as possible for those heavy showers.  Hmm, I will have a ponder on that.

My current plan (in progress) is to set up an interconnected 'control' water butt next to the lower IBC.  This control butt has two float switches which will be latched together to allow a good pump interval, a torbeck valve to refill from the top IBC as the water is used (it seems to be ok being fully submerged, fingers crossed), and will also hold the submersible pump.  Mostly the idea of doing it that way was to allow for tinkering and fiddling.  The top IBC has a float switch built into the lid to prevent overspill.  Just need to get the wiring/relays sorted now.  It all seems to be working ok so far, fingers crossed.  Will post some pics in due course when it's all done, I'm off to Glastonbury tomorrow - that should make it rain !

Cheers,  Bob.