Backyard Aquaponics
A place to discuss aquaponics

Hi all,
Having returned to South Africa I am busy building my first system in my moms backyard (yes I know you love pictures...they are coming!!)
System is a basic SHIFT PIST (all from recovered materials) the grow bed is an old concrete washing basin. I have build an autosiphon from a piece of black pipe inside a pvc pipe. The syphon starts perfectly and works like a dream BUT stops halfway through the syphon.
My guess is that the holes at the bottom of the pvc pipe(whats the fancy word, something like cranulations????!) are too big and therfore the presure drops as the water level goes down? Does this sound right?
If so can I simply fill up some of the holes with silicon?
Thanks for your time and help!
KarelM
Ps: will post step-by-step pics when system is finished

crenelations are the bumpy bits on castle walls, that you can shoot arrows through, and use to shield you under attack. We use the same word only cos of the similarity in shape.

In short no, it doesn't sound right.
Your siphon wont stop from lack of pressure.
It will stop if there is an airlock, or if there's a congestion in the lower line.
If you are using continuous inflow, it is possible, that with the decrease in pressure that the outflow slows to the inflow and you get equilibrium... this is not good.
If your outflow equals your inflow you should perhaps shorten your outflow pipe, make it as vertical as possible, and ensure there are no leaks in the fittings, allowing air to be sucked in.
if your siphon actually stops, then I have to guess a leak in the fittings, or air is being sucked through a deep vortex into the bottom of the siphon (however this is unlikely)
Some pics would help a LOT here. That's the best I can offer blind.

Hi KudaPucat,
If you shorten the outflow pipe ( I assume you mean the riser) wouldn't that just change the water level in the growbed?
Jack

what I mean, is the amount of pipe exiting the bottom of the growbed.
If this pipe is long, it creates resistance, backpressure, and can even form airlocks.

Thanks Kuda,
The exit on the auto syphon is a 90 deg bend and then about 75-100 cm of pipe.
I thing this might be it...I had presumed that the velocity of that is created by the sypholn would be enough to overcome that! Ok so I will have to have a re-look at that part....but it may take 2 weeks before I get out there again!
Cheers,
KarelM

OK so have we confirmed then that the outflow is matching the inflow?

If so.
The outlet pipe should be horizontally as short as possible.
it should be vertically as long as possible.
at the bottom, have a larger sized pipe that the outflow can run into.
Do it 'open drain' style... do not seal it. Allowing the water to freefall through air into the drain, means that the drain will not restrict the flow.
Here you need to watch it the first few times, because it's possible that the drain is not big enough to take all the water, and you will have spills, though I doubt it will happen.

Kuda, You're right on about the outlet...I had a trap to keep the pipe full and since I removed this part, it is now flowing as I believe it should...muchos gratias

jack

NP. Glad to help.

Some ppl have put a trap on the end of their outflow, to make the siphon harder to start, (the trap is open to air though, and only holds 100mm or so of water) you may wish to do this if you find it starts slow and and low.

Good luck with it all

Just to give a different slant on things. I find no problems with the length of the drain pipes. One of my drain pipes is 4 metres long.

The way I set up my syphons was to have a pipe going vertically to ground level to a 90 degree. They then rise slightly to the "airtrap". My pipes then turn to go into my sump, this section of pipe runs slightly down hill.

Pipes fall from the bottom of the grow bed. I locked the piping in place by screwing the fitting under the bed downward.



All the pipes are then raised about 3/4 of their width to create the "air trap".



With this arrangement my syphons break will break without the need for the small tubing on the bell.

I don't use the small tubing either... I'm guessing you have little problems with your because you pipes are so big. Are your drains bigger than your standpipe in the bell siphon?
If you have big enough drains, then they never fill (excepting where you raised them), creating the same situation, where water is not restricted by the pipe.
This is all I can think of to explain it.

The standpipes are Joels standard 25mil pipes, the bells are 50mil and the drain piping is 40mil.

KP you are right and I know you understand, but to make this as useful to others as I can:

The length of the vertical fall, coupled with the size of the drain pipes overcomes any back pressure issues. My pipes do completely fill but by having the corner of the pipes raised only 3/4 of the pipe width it means the water can start to trickle over. If I raise the pipes too far the back pressure increases and the grow beds overfill before the syphon works.

If the pipes are raised the right amount; when the water starts running faster over the top of the standpipe it gets to the point where the pipe completely fills up and seals at the high point. The moment that happens the whole water column within the pipe starts to move and the syphon is created.

It really is the same as the short "air trap" created by using an elbow. The only difference is that the entire length of the pipe fills with water and acts as the "air trap".

Hope this helps someone

Has anyone worked out lpm to activate a standard siphon. I chop and change mine from time to time and it would be a useful guide for standard pipes.

I have yet to read this anywhere in all my aquaponics research so maybe I'm the first, if not, others pelase back me up on this....

Bell Siphon Secrets
The crenelations work but not necessarily for the reasons you believe. My research this past weekend led me to using a bell siphon and it is now working without an air break tube also. At one point it was a continuous sihpon. This was due to gravity not being able to pull down the column of water that was trickling into the bell siphon (which was the same amount that I was pumping in). And why? because the amount of water going into the bell siphon had more siphon pull into the standpipe than gravity could pull back down on it to break the water tension from it going in it to begin with, but not enough pull into the siphon to pull more water in than the water supply was allowing. Did I say that? Yup. That is the whole point of the air break tube. If you increase the width and height of your siphon pipe (not standpipe), it should break on its own. But how you ask? When the siphon is at maximum siphon velocity, there is an amazing vortex in the siphon pipe above the standpipe. I got to see this happen during one of my tests because a siphon pipe I was using at the time was clear. If the siphon pipe is too short, it will diminish the size of this vortex, slowing down the siphon suction, and that is what you want to avoid unless you prefer to use an airbreak tube. My research shows that your can always go taller with the siphon pipe but you can only go shorter to a point where it starts to fail.

One thing that must happen is the crenelations at the bottom of the siphon pipe must be big enough to allow enough water flow through to support maximum velocity of the siphon. It is better to have too many than too few, because it doesn't take much support usually to keep the siphon pipe standing. If you use a pipe with no crenelations or slits and the bottom is straight across, it will seriously limit water flow.

If your bell siphon does not stop, the above paragraph is your problem. The vortex is not strong enough to pull the last of the water up to help break the water tension. Ensure you have enough water flow at the crenelations and extend your siphon pipe height. If that doesn't do it, use a wider siphon pipe, because you are choking the siphon, it can't get enough water through to reach maximum siphon velocity.

If your bell siphon never starts but only has output matching input, the standpipe (the outlet pipe) is too wide. The amount of water coming in is too slow to create the waterlock the siphon needs to begin properly. Reduce the width of your standpipe or at least reduce the width of the top of it somehow with an adapter and give that a try.

If your bell siphon does not start fast but instead just slowly starts, (at one point mine took 5 minutes from the first constant dribble drops until it 'caught' and actually siphoned) it could be that you need to increase the height of your siphon pipe to allow enough room for the vortex action. Taller siphon pipe may look funny with your system but it will work a whole lot better! If you want to hide it and make it look better, put a hand puppet scarecrow over it.

My standpipe (outlet pipe) is the same size as my tubing that is pumping in water. My siphon pipe with cap (and no airhole break) is twice the size of my standpipe and has plenty of crenelations. I'm sure that I could try a large enough siphon pipe that would break this theory, in which case, that would probably make a good size to use as a protective shroud (with water holes) to keep material from entering the other parts.

Some where on the forum is a thread that has calculations about the needed sizes of things for proper functioning bell siphons. I think Ell Kay Bee probably did much of the pioneering work on bell siphons in Aquaponics for this particular forum.

I've read and re-read the "secrets" section above, but I still can't get my new bell siphon to work.

First of all, some definitions.
Am I understanding this correctly?
As Thorn has in his post-

Drain pipes:


Siphon pipe:


Standpipe or outlet pipe (albeit very short):


Is that all correct?
Next post - my setup.