Backyard Aquaponics
A place to discuss aquaponics

Is the 20mm standpipe sealed around the 12mm piece or does the 12mm piece provide an airbreak?

no it is not sealed it just sits in the standpipe and rests on the bottom of the 90mm return to sump. i slash cut the bottom of the 12mm piece.

By restricting the flow you've created a trap without the bend in the plumbing. Nice.

Bluefin, I like the idea, but don't understand the function.
Can you explain in detail how to affix the 12mm pipe and how then it will cause a trap? this looks to be EXACTLY the kind of thing I need, and engineered very simply.

Another drawing in more detail would be very much appreciated.

Bluefin

So this is a simple restriction? If so then I guess it means the short lengh of pipe at that point is completely filled with water therefore creates suction?

I'll try to explain it, hopefully I get it right.

During the drain cycle, water rushes out the 20mm pipe, completely submersing the 12mm pipe with slanted cut at the bottom. When the bell siphon drains enough, it could slow to a dribble, and this is where the 12mm pipe comes in. By the time we get to dribble, the 12mm pipe is no longer engulfed with water and the water level has dropped below the start of the slant cut (or water is only draining AROUND the 12mm pipe), thereby allowing air inside the middle of the standpipe water flow and breaking the siphon action.

Thorn you may be right, but I really am gonna need a sequence of diagrams words rarely work for me unless you can fit the definition into 1 sentence Afterall, I'm an engineer, we do, we don't think and we certainly don't read well;-)

ok. I used to install a lot of urinals and associated pipework. The wall mounted cisterns used an autosyphon. At the bottom of the flush pipe dilivering water to the urinal face is a restrictor called a sparge that directs the flow accross the urinal. The sparge is usually a chromed cast brass fitting with an inlet in the top for the pipe and a narrow slot the width of a hacksaw blade for the outlet. When the cistern fills and the autosyphon starts to overflow the water gets to the outlet but is restricted the water starts to back up in the pipe untill the syphon kicks in. The restriction no longer seems to affect the flow and with a gurgle and hiss the water rapidly drains from the cistern and disperses across the face of the wall. Coincidentally if you remove the restriction on the end of the flush pipe it is near impossible to get the autosyphon to work correctly. So back to my bathtub setup. My empirical findings would lead me to believe that the 12mm pipe which has a gap around it of approx 3mm and is just sitting loosly in the standpipe will allow water to pass around it and through its bore. The water backs up in the standpipe and then must reach a point where the volume collected in the standpipe is too great for the restrictor to hold back. The syphon kicks in and water is able to pass through and around the 12mm pipe with ease. It does work. I can cut the level of flow into the bath right back and the syphon still kicks in. Without the 12mm pipe i need to crank the flow up to get the auto syphon to work. The pump is delivering 18000 lts per hour through 40mm pressure pipe to 11 outlets controlled by 20mm ball valves. I will take some readings this arvo and post them tonite when i get home from work. Try it out you will be amazed the difference it makes. Oh i guess it would be similar to inverting a bottle of water and spinning it rapidly. the water dribbles out initially and then a vortex happens and the bottle drails in a flash, maybe? I will try to post another diagram later.

Wow, I didn't understand that at all

OK. I get how a siphon works.
I get how a dynamic restriction will aide a siphon.

What I don't get is how the 12mm pipe produces a dynamic restriction, or any at all for that matter... I'm so confused.

I'd LOVE to try it out, but can't picture the 12mm pipes installation properly.

If you'd be so kind as to provide assembly instructions, perhaps with a diagram, I'll build one and see if I can't understand it then.

I really like your idea as it will get my siphon going without needing to dig up the beds or do anything fancy.
The problem is, the solution you offer is so elegantly simple, I can't see how it works

See if this site helps
http://www.siphons.com/operation.html

Not really. I understand siphons. I'm interested in Bluefin's special restricter.

ok, you know how you can start a syphon by filling up the long leg of the syphon with water holding your thumb over the end and releasing it to start the syphon. That is whats happening the 12mm pipe restricts the flow the standpipe fills then the weight of the water falling in the stand pipe creates an area of negative pressure at the top of the standpipe and atmospheric pressure does the rest. To test my theory remove the standpipe cover, insert a 150mm piece of 12mm pipe and replace the standpipe cover and fill the gb. That is providing the dia of your standpipe is 19mm.
it is the last day of the school term so i am off to the pub to celebrate will post photos tonite.

Are you saying that the pipe in the center gets no flow through the middle? Therefore it restricts flow until the siphon starts in earnest,
then due to the deluge the water can go through the middle?
Wow.

Ok, so couple of confirmation questions.

Does the 12mm pipe sit in any water? or is the 90mm drain empty?
Does this work by virtue of the face that water only flows down the sides of the pipe?