Secondary tank working on gravity

[bowlingo]

Hi all,

I have been designing and building a hydroponics system thats controlled by mobile phone for the last few months in my spare time. A friend who I have known since school has owned a hydroponics business for the last 10 + years and he asked me to design a system knowing I am into electronics....

With hydroponics you are supposed to let tap water stand for 12 - 24 hours for the chlorine to disipate.

I have a main 100 litre (25 gallon) reservoir tank of which there is a solenoid on it that opens on phone command...

I have thought of a way of using a secondary water butt with a ball valve on it raised from the ground on blocks, the ball valve will let in the tap water by a jubillee'd hose tail to the top of the water butt then the bottom off the butt will have a 1/2" pipe attached to the inlet side of the solenoid.

What I am trying to calculate is the pressure or get an idea...at the moment using tap pressure attached to the solenoid it takes 15 - 20 minutes to fill does anyone know if the pressure in the water butt will be enough to fill the reservoir in around the same time?...another probelm is the water butt will start to let in water as its emptying so it wont be releasing the water thats been standing into the tank so I need to work out a way of making it delay mechanically?

Thanks

 

[doitall]

I thought Nutty professors just had bright ideas and did their thing.

Can you empty the butt as fast as the mains pressure filled it ??

Yes if the outlet pipe is large enough.

Solenoid, float switch or mechanical should solve the last question, even a delayed timer would hold the valve shut.

 

[Space cat]

does anyone know if the pressure in the water butt will be enough to fill the reservoir in around the same time?

The flow rate through the solenoid will be roughly proportional to the pressure difference across it. To find the pressure difference between the butt and the reservoir, you measure the difference in height between the two water levels. You could then convert this to bar (or Pascals if you prefer) but it's easier to do everything in terms of head of water.

Tap pressure varies from place to place but you can measure it. For the sake of argument, let's say it's 2 bar. That's equivalent to a head of water of about 20 metres. Chances are, your water butt isn't that high! Since fill time is inversely proportional to pressure difference, you can expect it to take a lot longer than 20 minutes.

?...another probelm is the water butt will start to let in water as its emptying so it wont be releasing the water thats been standing into the tank

That's not as bad as it sounds. What you have there is a continuous process. The release of chlorine from the tap water isn't something that happens at a steady rate until it's all gone. It's a diffusion process so the rate of loss is proportional to how much is left. Think of an RC circuit running down. What you need to do is adjust the flow rate so that, on average, the tap water spends long enough in the butt before it goes on into the reservoir. I'll let you do the sums on that one.

 

[doitall]

Space Cat pressure and Volume although related are not the same.

You can get the same volume ltr/min from 0.2 bar as you can from 2bar, simply by increasing the pipe size.

 

[bowlingo]

Thanks for your replies...

The solenoid valve on the main tank is 3/4" with a reduction due to a hose tail on it going to a 1/2" hose pipe..so to increase the flow I am asuming I would need to buy a bigger solenoid of which are expensive...

If the main tank is 100L and the water butt is 310L

http://www.wickes.co.uk/invt/158983

And the 310L tank is raised off the floor on blocks (im thinking thermolites) so that the 3/4" outlet on the butt is slightly above the solenoid valve on the main tank...(solenoid valve is at 400mm from floor level and the output pipe of the butt is at 500mm from the floor level) would the weight of the butt (3xs what is needed) push in at a good flow due to the weight of the water above?

If there is this much water in the butt then im asuming it wouldnt matter that the ball valve is filling up as its draining out due to the water being well below that has already had the chlorine evaporated?

Thanks

 

[bowlingo]

Now im wondering how im going to get fixings onto the round water butt..

i.e if I go and push a 3/4" ball valve into the top of it I wont be able to get it to seal unless it has curved washers or something

If I cut the existing drain tap out of the bottom of the butt I will then have to cut something like a tank drain off into the bottom of which is curved

I have just put my calipers on the mains tanks solenoid/ball valve thread and its 3/4" so it will be 3/4" - 3/4"

 

[Space cat]

You can get the same volume ltr/min from 0.2 bar as you can from 2bar, simply by increasing the pipe size.

Very true. If I remember my A-level physics correctly, flow rate is proportional to (pressure difference) x (fourth power of diameter) / length. Changing the diameter from ½" to ¾" will, theoretically, increase the flow rate by a factor of five. Keeping the pipe short will also help.

I have just put my calipers on the mains tanks solenoid/ball valve thread and its 3/4" so it will be 3/4" - 3/4"

It's the inside diameter that matters.

solenoid valve is at 400mm from floor level and the output pipe of the butt is at 500mm from the floor level

It's the difference between the two water levels that matters.

If the main tank is 100L and the water butt is 310L

If this is all operated by phone command from a distance, how will you know if it's flooding? Do you have a float switch in the reservoir to shut the solenoid?

-- it wouldnt matter that the ball valve is filling up as its draining out due to the water being well below that has already had the chlorine evaporated?

That's not quite true. There's nothing to stop chlorinated water from diffusing downwards but it would help if can arrange for the ball valve to send the water out horizontally instead of squirting it down into the depths.

 

[bowlingo]

If this is all operated by phone command from a distance, how will you know if it's flooding? Do you have a float switch in the reservoir to shut the solenoid?

the main reservoir tank has its own ball valve of which is its mechanical protection. Once the command is sent from the phone it activates a timed relay that opens the solenoid for 0 - 60 minutes...20 minutes works well with the ball valve only having to work for a few minutes

So as of my last post do you think it will work in the following situation (max allowed time = 30minutes)

310 litre butt on blocks with the outlet at 500 mm with about 1 metre of 3/4 inch hose connected to the 3/4" solenoid valve at 400mm using jubilee clipped 3/4" hose tails.

mains water pressure 1/2" hose going into a ball valve at the top of the butt but flowing in horizontaly

...ive still no idea how to get the fittings to go onto a round butt though (all this talking about butts is making me feel unusual)

 

[Space cat]

You still haven't said how high the water level in the butt is above the water level in the reservoir. I'll pull a figure out of the air and say 1m maximum. Up do now, you've been working with mains pressure water at an equivalent height of some tens of meters. To get a similar flow rate from a 1m head of water, you'll have to at least double the inside diameter (bore) of your connections. That's all of them: outlet, hose, solenoid, inlet valve, the works.

 

[Boilerman2]

The question that keeps going round and round in my mind is WHY do you want to control such a mundane operation via mobile phone telemetry????

I'm due to retire in 14 years and to be honest I have so much still to do I couldn't be a***d with such a pointless project

 

[Dan Robinson]

Dat way ya dornt 'ave to be nearby hwhen de babylon turn up innit brederin

 

[bowlingo]

The question that keeps going round and round in my mind is WHY do you want to control such a mundane operation via mobile phone telemetry????

I'm due to retire in 14 years and to be honest I have so much still to do I couldn't be a***d with such a pointless project

you dont know anything about the project..ive been working on it for 4 months at a cost of around £2K It has 15 input commands and 16 output commands, 2 x cameras, water sensor alarm, smoke alarm, motors, dosing pumps etc etc

The UK, US and Canadian hydroponic forums certainly dont consider it pointless

 

[bowlingo]

You still haven't said how high the water level in the butt is above the water level in the reservoir. I'll pull a figure out of the air and say 1m maximum. Up do now, you've been working with mains pressure water at an equivalent height of some tens of meters. To get a similar flow rate from a 1m head of water, you'll have to at least double the inside diameter (bore) of your connections. That's all of them: outlet, hose, solenoid, inlet valve, the works.

Thanks...Looks like im going to have to re-think it so it either takes longer to fill or have another pump

 

[Space cat]

have another pump

That would solve a load of problems at a stroke. No need to put the butt high up for a start and no need for an expensive wide-bore solenoid valve either. Just make sure the reservoir water can't syphon back out into the butt when the pump stops.

With decent sized connections (¾" / 22mm) a standard CH pump should give you a decent flow. (You should be able to confirm this from the pump's technical data.) I would put a float switch in to stop it when the reservoir is full otherwise it'll be running stalled against the closed ball valve - which it won't like one bit! Let the ball valve act as backup only in case the float switch fails.

 

[bowlingo]

have another pump

That would solve a load of problems at a stroke. No need to put the butt high up for a start and no need for an expensive wide-bore solenoid valve either. Just make sure the reservoir water can't syphon back out into the butt when the pump stops.

With decent sized connections (¾" / 22mm) a standard CH pump should give you a decent flow. (You should be able to confirm this from the pump's technical data.) I would put a float switch in to stop it when the reservoir is full otherwise it'll be running stalled against the closed ball valve - which it won't like one bit! Let the ball valve act as backup only in case the float switch fails.

I am thinking a small 3/4" bilge pump on the bottom of the water butt, connected to a timed relay of which will trigger with the main reservoirs solenoid valve and a ball valve at the top.

My problem now is how to fix the ball valve and outlet fittings to the curved butt. I could now use a smaller butt i.e

http://www.diy.com/diy/jsp/bq/nav.j...specificationsSpecificProductType=water_butts

The bilge pump is here...

http://www.ebay.co.uk/itm/JOHNSON-B...tEquipment_Accessories_SM&hash=item336a0a39e4

I will screw it onto a heavy plastic slab with the 4 corners tight against the edges of the butt so it stays still. I have one of these on the system at the moment that I use to empty it...it empties 100 litres in 7 minutes on a 8 metre hose.

Thanks