Backyard Aquaponics
A place to discuss aquaponics

I have one siphon driving me crazy. It is an affnan setup in a continuous pumping flood and drain. It is in one of two newish beds, and the bell is nearly identicle to the other one which works fine.
This one starts no problems, then stops but as the water level starts to rise it starts to dribble then comes to equalibrium with the incoming water so stays at 4 inches deep.
The siphon obviously is not breaking properly, but I am out of ideas. The bell has two horizontal 10mm slots for the water input and has a 8mm breather tube which seems to do nothing. The end of the breather tube in maybe 20mm above the slots.
Any thoughts??

hahahahaha.... The joys of siphons.... Sorry, can;t be much help, but couldn't help but giggle as I understand the crazy feeling... Got any pics?

does your drain pipe have a breather and is it trying to run uphill, I just had the same problem that is what was wrong with mine, putting the breather on the drain and rechecking the level fixed it straight away, I will upload a photo if you need one

Could be that it's not air tight.
Check sealing, especially around Bleed tube at top entry to the bell.
Just using water and checking for leaks is not good enough,: water tight is not air tight!
Is there a relief vent? (ie opening to atmosphere on the upstream side of your siphon drain) for the siphon water to get away freely?

Cheers IanK

Sorry I must be missing something, but I was under the impression that affnan siphon does not have a breather tube...

I'd Be Making sure its running downhill to the Sump to Richo, i had so many issues with mine until i put a good 50mm of fall on them all now no issues at all, i also got rid of my breathers.

also do you have too much flow?? but sounds to me like maybe you have a Bow in the drain where water will be locking and causing it to try run up hill.

While on the subject of Affnan siphons, I see that many people manage to get the large reducing coupling for the top, the "funnel" as such. Now pretty much every one that I've seen had a nice angled slop on the inside where it goes from the large diameter to smaller. I've only managed to find ones that have a big step on the inside from the large diameter to the smaller. There's no lovely conical shape just a stepped reduction.

Has anyone used these in an affnan? Do they work as well as the angles ones?

Just in case this is useful...

I had the same problem once, and it turned out to be a meniscus had formed between the bell and the breather so the breather was sucking water up even though it was 1 cm above the water. (it was a very narrow breather)

And...

if there are not enough holes in the BOTTOM of the media screen it can reduce the flow when the tide is almost out, to the point where the siphon hickups then starts again but with just a trickle. When that happens out-flow can match in-flow and it can stay that way forever. As the siphon almost stops, the local tide within the media screen can rise up from the flow still entering through the screen, and the small amount falling back out of the bell and restart the siphon again.

The rate at which your siphon flows still depends on the head. ie it depends on how high the grow bed's water is above the outlet at the bottom of the standpipe. In my small test system that's only 5 cm or so, so there is very little pressure.

The height of water at the end of the cycle ie when the tide is almost right out is lower, even though the water actually goes up to a set height in the siphon, its the head that sets the exit flow rate. So as the tide goes out, the flow reduces. If the reduced flow matches the input of the pump then the siphon reaches an equilibrium and the level inside the media screen will settle down to a constant.

Look inside the media screen and see if you can see water squirting through the holes. If you can it might mean there is a greater water level outside (in the GB) than inside the screen. That might mean there are not enough holes in the screen. To test it just lift it up a tiny amount to let some water flow under it. Don't over do it and let in any media, or better still put a tea strainer under your standpipe when you do it to catch any media and protect your pump.

If the flow out of the standpipe is reduced in any way, especially at the low pressure (tide is almost out) stage, you can get a situation where equilibrium is reached. Make sure there is no way air can be trapped in your system after the bottom of your standpipes. I find the best way to be certain of this is to have your standpipes dump into fresh air rather than a sealed drain pipe. When the siphon is stopping, air gets sucked into it. if the first tiny bit of air can collect in your pipes, and it comes in at just the right rate, it can reduce the flow just enough to make the system settle into a situation where the flow in equals the flow out. This is easier than it might seem, because if the air is coming in gradually enough, the incoming air makes the siphon suck less, reducing the amount of air being sucked in. If the air can be trapped, the system self regulates the amount of air it takes in, to the point where equilibrium is reached.

For a siphon to work it needs to have a flow in and a flow out that are within the siphons ability to start and stop. Each siphon, depending on its size and shape will have different maximum and minimum flow rates that it can operate within. If you have 2 almost identical siphons, and one is working and the other isn't, it could just be the one that is working is only just working. ie its working right at the extreme of that bracket that allows success. The tiniest variation in flow to the second one, or the flow through the media screen, or a bit of air trapped in the system could be just enough to take it out of that successful area.

Depending on your lengths of pipes and height of head, its possible to have a siphon trigger properly even though there is some air in the drain. But if it's sitting right at the extreme of the allowable flow when it comes to the stopping stage, its possible for that tiny bit of air to make it fail.

Even though its often helpful to use raised sections in your drain pipes to trap water etc, if you make them fall straight down into fresh air, then control the flow into your garden bed, you will find it very easy to get siphons to work reliably.

You might need to adjust the flow to the growbed to get a siphon to work within its maximum and minimum required flow rates.

I should stop now

Hi Mantis,

Sounds like the air isn't able to come back up from the bottom or you have to much flow going in. The 2nd one is easy to find out. Once the siphon starts, stop the water going flowing in and if it breaks properly theres your problem.

The 1st one might be a bit harder depend on how your plumbing is set-up as mentioned above you may have an up-hill slope some where causing an air lock?

Also mentioned by ivansng, for an affnan to work you do not need the breather hose.

Another issue I have had with Affnans is if the barrier holding the media back does not have holes or access for the water to enter from the very bottom of the GB. It really needs to be able to suck water up from the very bottom.

All these questions can be answered if you can see what's happening inside the bell.

Can I suggest, if I may you change the bell over for a clear plastic bottle? Just cut the bottom off and then cut some V's into the bottom. That's it done, slide it over your stand pipe and you will be able to see what's going on.

This video might help best explain:




Since then I have started using tall water bottles as they have more height and are better suited to a 300mm deep GB.

Any chance of some photos showing both the bell and the stand pipe in the GB?

Hope this helps?

Grrrrr, two new bells and much swearing and cursing later and it was that the beds had sunk over and inch and the return pipe was running uphill
Jacked the regum bearers up and put some boards under them to lift them back to the level of the byap beds and now I have a half inch fall, and the siphon farts and stops no problems
Thanks for all that replied

*storms off to shed with pint glass in hand*

Edit: saw all the replies and I sure they will be helpful

Mine are all just stepped reducers and they work a treat. I only have one siphon thats not an affnan and its the only one I ever have issues with getting to start.
You only need a very slow flow into the bed for the affnans to kick in.

I had one of them working in my test system with out an issue. All you need is some sort of reduction for it to work.

So it has a larger Breaking surface so that more water flows into area of the smaller pipe

I know this is not your problem Mantis but Ivan is right, having a breather tube on an Affnan is redundant and just another thing that could go wrong.

EB, my Affnans are 2 stage step reductions, no smooth angles at all are have worked flawlessly for about a year.

I love the way the Affnan siphon has taken over the AP siphon world, they are clearly a superiour design

Generally, if the siphon will not start there is not enough water flow.....if it will not stop there is too much