Backyard Aquaponics
A place to discuss aquaponics

An auto siphon system, the idea is to have a small continuous flow pond pump running with a slow flow rate to flood a grow bed and a large drain pipe to empty the bed quickly using gravity feed – the smaller the pump the less drain on a backup system in case of a power failure.

The siphon consists of:
150mm outer covering pipe
the pipe is a barrier to hold the grow bed medium from the siphon but allow water access,
the pipe is upside down in Pic 1, this is to show the 20mm wide support legs and the pieces cut out (10mm deep) to allow water to flow under, the vertical slits are to assist the water flow, it is also a good access area to the siphon.

40mm vertical drain pipe
the top of the pipe was cut to a height of 250mm above the grow bed floor,
3 pillars of 10mm wide are used to support the 65mm siphon pipe,
Pieces were cut out to a depth of 12mm – the area of the cut out pieces represent the area of the 40mm pipe, this is to allow full water flow equal to the drain pipe size,
silicone sealant was added to the side of the pillars to ensure the siphon pipe did not move in and cut off one of the holes and restrict water flow

65mm pipe and end cap (siphon pipe)
the 65mm pipe was cut to 235mm allowing for a 15mm gap for water to flow under and up the siphon pipe
the siphon pipe needs to be a minimum of 50% greater than the drain pipe so that sufficient area is available for maximum water flow to the drain pipe.
(20 or 25mm drain pipe could be used with 40mm siphon pipe)

3mm air tube
the air tube is used to suck in air and make a clean break of the siphon seal when the grow bed is empty.
Position the tube end so that it is approximately 25mm below the bottom lip of the crenellations on the drain pipe, this is so air is blocked from entering the siphon/drain pipe chamber when nearing the top of the siphon pipe, the air tube should then rise above the grow bed water level, this makes sure the tube does not act as a siphon until the big one kicks in.
the other end of the air tube is connected to the outlet pipe going to the fish tank (see pic 2)

As water rises, air is forced out the tube and water level rises between siphon and drain pipe walls, water then cuts off air tube access and pressure builds in drain pipe and U-bend (see pic 3), air is pushed out of u-bend and water continues to rise in siphon pipe and spills over until siphon starts.

U-Bend acts as an air trap (Pic 3)
A 90 degree elbow was cut off so that water is about 5mm deep in the pipe and thus traps air between the water level in the siphon pipe and the U-bend, in total there are 4 elbows including the one under the grow bed.

Siphon cycle
Water is pumped into the grow bed and initially air is pushed out of the air tube as water rises inside the siphon pipe, the water level cuts off the air tube outlet and pressure builds pushing out trapped air through the U-bend and the water continues to rise and flow over the lip of the drain pipe until the water level reaches the top of the end cap and the siphon kicks in (see Pic 4).

Water will be sucked through the air tube in a venturi action and as water level drops, air is then sucked down and aerates the water.

The water level drops below the siphon pipe and air is sucked under the pipe and into the top of the siphon pipe, now the water in the drain pipe is trying to drop one way and the water trapped between the drain and siphon cylinders is also trying to fall back down into the grow bed and so air is sucked into the drain pipe via the air tube and the siphon seal is broken and the cycle re-commences.

Points to mention
the siphon is self priming in that:
a. I removed the siphon pipe altogether and just let the water flow over and down the drain pipe before putting it back on,
b. I cleaned out all the water in the U-bend and it just filled up from overflow then kicked in.

Height of the air tube should be at least 25mm down from the bottom of the crenellation lip, this is to enable the velocity of the water to be sufficient so that when air is sucked through the tube the water will pull it along to the fish tank and not allow it to go back up into the drain/siphon chamber and stop the siphon action, the height was not so critical with 3mm tube but increasing the diameter would increase more air flow – I only tested with 3mm tubing.

Height of the air tube is not critical either as long as it cuts off the air supply before the bottom of the lip on the drain pipe and is above the level of the bottom of the siphon pipe so that it can suck in air to break the siphon seal – the higher the better as it adds to water aeration.

Water flow rate through the 40mm drain pipe is approximately 5,000lph, this means that the maximum pump size per 40mm drain pipe using gravity feed should be no greater than 2,500lph.

I tested down to 400lph (with a pump rated @ 1,000lph at 1 metre) which means 200lph each for 2 grow beds but it is the rate the water rises in the grow bed to overcome the overflow down the drain pipe before the siphon kicks in needs to be overcome, with larger grow beds than 100 litres then a larger pump flow would be needed – the other point with pump sizes is the smaller the pump the smaller the intakes are and easier to clog.

Tank water turnover should also be taken into account when selecting a pump, figures up to 3 times per hour have been stated, so using this ratio the water flow should be in the vicinity of 600lph for a tank size of 200litres.

Thanks for clarifying it for me... I love it mate...

It looks real nice ...

why all the holes and ridges ?

Can you explain a little more how it all works ,, .. takes me a while to get my head around it ..

Doh .. I am thick sometimes ...

The thing I found .. (more so with shallow trays) .. was reliability of the fill break and empty break levels ...

with short siphons ..... sometimes they just get to the stage where they just "flow" ... either in full or empty level positiion ..

Deeper tanks .. no probs ... siphon works 100 % .... every time!

probably havent been payin as much attention as I should have been to this part.......there is just so much to take in....BUT.............is it necessary to empty the bed quickly , if so why?

I take it you mean on the 150mm pipe, that's to allow free flowing water from the medium to the siphon, if its the ridges on the upright drain pipe, the water flows between them into the drain pipe and back to the tank



No real need to do it quickly but it needs to be done faster than the inflow, the alternative is to cut off the flow at regular intervals and let it drain at its leisure.

A 40mm pipe dumps it at that rate, by using a smaller drain pipe size would decrease the flow rate, just means re-calculating the figures.

The main reasons I kept on with it is its simplicity and ease of maintenance, plus it is an alternative to the other flood and drain concepts - each siphon type has its own advantages/disadvantages, this is just another choice with its own peculiarities

see how we go - I'll leave out the 150mm pipe, it just fits over the whole siphon thing.

the 65mm pipe and end cap slides over the upright 40mm drain pipe, what that does is form two walls which the water rises up in between as the grow bed fills and then slides down the drain pipe to the fish tank, this is the normal flow of the water.

Due to the size of the pipe (40mm), a trap is needed to start the siphon working and so the u-bend is used so that air cannot escape and pressure then builds as the water tries to rise up inside the siphon pipe until something has to give - in this case the path of least resistance is out through the u-bend (only 5mm of water depth), air is forced under the u-bend and suction occurs which draws water over the lip on the drain pipe and out into the fish tank (very quickly).

The air tube is only to suck air back in after water has ceased flowing from the grow bed and break the siphon seal and the cycle begins again

Thanks mate ...

I wanna do this ... and will try what you have done ...

Looks like it works for sure!

I still don;t quite understand the reason for all the fancy cuts .. especially those that look like a castle ..

Would there be a way to use one simple diagonal cut to take care of all that?

Very nicely done. Draining the beds fast I'd think, would also allow for more aireation in the return to the tank. Will be studying your work more closely as I but my growbeds together. Good job.

Please note - I edited the original post in reference to 3mm air tube and its height below the high water level.

The height should be around 25mm or less from the lower lip on the drain pipe, this is not critical with 3mm tubing but larger tubing would suck in more air and if the water velocity in the pipe is not great enough air could flow back into the siphon/drain pipe chamber and stop the siphon action, once the water is flowing freely this would not be a problem (Mod[xxx])

Les

Crenel – one of the gaps between the raised part in the castellation on a battlement, any structure or ornament resembling these in form
I thought it was kinda apt – my own little siphon castle.



This could be done as long as the actual area for the water to flow through was sufficient to take the volume of water - 40mm pipe has a cross sectional area of 1256mm2,
the other point would be that the cuts would be deeper and water would commence flowing down the drain pipe earlier.

I found making my castle quite easy to do, mark the verticals and horizontal lines with a pencil, cut verticals with a hack saw, cut along horizontal line between the vertical cuts (carefully) with a hack saw and then a quick clean with a knife and sandpaper, try it on a scrap piece of pipe

wuddya like to borrow me chainsaw mate???

that it does - trying to get 2 beds up and running then take a pic of both draining at the same time - not gonna let Monya and his fire hydrant stay as top pic

just a quick reference for imperial/metric (approximations)
25.4mm - 1 inch
3mm - 1/8 inch (inside diameter of the air tube)
40mm - 1 1/2"
65mm - 2 1/2"
150mm - 6"

hope this helps

Les

Hi Les,

I have concluded that with my growbeds lower than the fishtank water level I am creating a syphon everytime I turn the pump on.

That in itself is not a problem, a non return valve somewhere up high will break that syphon easily.

But I figure why not use the syphon and not run the pump in the fishtank?

This would mean that I have to change the system to fill up slowly and then drain each growbed fast, for which your syphons seem to be just the thing.

One question: What is stopping the 65mm pipe from floating up with the water movements? Is it simply kept in place by its own weight? Sitting loosely on top of the 40mm pip's crennelations?

And do you know how the syphon works with various speeds of water filling up in the growbeds? If it fills up slowly, does the syphon still work? Or is that where the waterlock further down in the pipe comes into it?

I think I will just haev to start some trial next weekend, but in the meantime I may as well get as much info as I can from the Forum.

Karel

What happens if the pump that returns the water to the fish tank fails (or the power goes out) and all the water syphons out? With two pumps you run that risk anyway, but if the power goes out no water goes out of the fish tank.

Just something I thought worth mentioning.

Nova

Yeah Nova,

I thought of that. I will simply be a matter of undoing the pump at the coupling, which I deliberately glued in to be below water level. Then the pump can just sit there doing nothing until I need it again to start up the syphon, and if the water drops to below the level of the pipe, well then it will suck air, break the syphon, and the tank will never run all the way empty.

As for the sump pump at the bottom end of the system. Well like you said, if teh power fails, or the pump fails, then either way I will loose as much water as it takes until the syphon in the tank draws air. But that would happen anyway even if I would run the pump in the tank.

Karel.