Backyard Aquaponics
A place to discuss aquaponics

Rupe, the last time i needed to do something similar, (not AP related) I placed a piece of Flat PVC in the pipe, drilled and tapped a number of radial bolts and sealed with roof and gutter silicone. This held 100psi of air no probs. It's a lot of work,but hey, how badly do you want to do it?

Got a big bit of pipe sitting there doing nothing Kuda....

Well then, can you get a hold of 8-10mm PVC flat? Stainless would work too. Have you got a lathe or some1 who can make it round for you? drill and tap I'm sure you can sort out. 3-4mm tap, min 6mm wall thickness on the flat. lotsa silicon.

Had pictured it mentally before, but wasn't confident that it'd hold overtime with flood and drain.....

See, this is why we need an engineer on the forum

So Ive taken all the media and water out of the top GB , ripped off the outside pipe of the autosiphon , and Im ready to silicon it all back together and try again when I think " hang on a minute , Ive been through all this before" .
BAck when I built my own marine tank I stuffed around for weeks trying to perfect a little surge box to go on top of the tank to simulate waves crashing down into the rocks/reef where the fishies lived .

same principle as the pipe-within-pipe autosiphon I suppose , but this is one that Ive actually made WORK before , so Im gonna give it a shot this way & see how I go .

Im wondering if anyones tried this type of siphon before and if its gonna cause some unforseen problems ?

My only worry is that regardless of how I do it , the 40mm pipe that Im using is still wayy to big for the pump :

pump pushes water up almost 2m , takes a bit under 15minutes to fill 100 litre GB , maybe the reason Im not getting enough suction is that thwe pipes too fat .
Well , Ive got the materials on-hand to try this next U-bend way of doing it , and I'll try anything first before another bloody trip to bunnings .

The diagram below shows how Im gonna build it . The water fills up to the top of the curve , Im hoping that the pocket of air in the top of the 40mm pipe isnt strong enough to withstand the pressure of the full GB and BAM! the whole thing drains quick smart .

Fingers crossed , here comes the silicon

Your fill level as marked, is where the siphon will Start dribbling.
To get the siphon to start properly (you should only need 25mm pipe) the waterlevel will need to clear the top of the pipe by about 2 inches.

My suggestion is lower the two elbows where you have marked 'fill level' by about 2 inches, maybe 1 at a time. You need a certain amount of pressure to force the air (which compresses) out of the pipe.

you will see the pipe start to dribble, and then as the water rises, suddenly start to Really flow hard.

heres some new pics

first & second - the 40mm U-pipe thing ready to go in
and then installed , with shadecloth cable-tied over the holes to stop the media going into it aswell .

Youre right - the suction level was near the top of the curve , id forgotten that .
It was lowered a bit in cutting anyway , so it worked out not to be too high .

This was a little experiment for today to a) try not to go to bunnings , and b) find something to do cause its 40 degrees and too hot to work .

the problem was still there - the 40mm pipe is way too big for this size system / pump inflow . Id filled it near the curve , then backed the hose of to be the same flow as the pump was pouring in , and it couldnt push enough water into that fat a pipe to compress the air enough to siphon

Ends up my partner called , and said " do I need to pick up anything on the way home" ...
heheheh , yeah , go to bunnings for me !
So Ive taken all the 40mm fittings out , bolted & siliconed a new acrylic plate over the old hole , and Im about to build a new standpipe out of 20mm pipe , with a 40mm outer pipe to stop the medie getting in .

If THAT doesnt work , I'll gut the bloody thing tomorrow and put a 20mm U-bend siphon in same as the one I built today , which is getting thrown on the pile of "stuff to use later

It won't work this way in my lowly opinion~ you will never push all the air out of the elbows in order to create a siphon effect and if your pump can handle that large a flow you will not stop the siphon when it does start. This will just create a drain that is set to the level of the top of the elbows which begins at the bottom of the bed.

Ive gotten this type to work before , admittedly on a scale half the size , for a surge box on my old marine fishtank , maybe its the size that stopped it working right , yeah

Ive taken it all out anyway & here's the pics of what Ive replaced it with :

Outer pipe ( "premium pipe" ? or something - its a bit smaller than normal 40mm plumbing pipe , but its still got 40mm written on the side of it ) is 40 mm , no cap on top yet till I can look inside & see it work . I'll cable-tie the shadecloth back on it to cover the holessso the media cant get through / block it , but maybe this will reduce the flow too much ..

the bottom of the outer pipe , at the base of the GB has got another two bits of pipe around it - I just cut vertical slits in them so they expanded to fit around , then filled the guts with silicon . Did that so there was more surface at the bottom / underneath the outer pipe for the silicon to stick .
I tried blue-glue but it didnt hold / melt the acrylic plate the same way it glues the pvc tight

The top of the 40mm outer pipe is 2cm above the inner pipe , which is standard 20mm plumbing pipe . then theres the new piping for underneath which fits perfectly along the 2nd GB and shoots straight down into it ( plus the fancy fireman type valve that I couldnt resist using , it just looks too cool )

Now to have dinner and try to forget about it so the silicon has time to dry

maybe you need to do something about the hormones in your diet

You obviously have a green finger (in fact several).

heheh , good old photoshop - i couldnt resist

Hi B, I think you'll need a lot of flow to get the siphon to start through the two elbows, put together they're not very close and there is a lot of volume in the space between them. I think the pipe in pipe would start easier than a u bend like this because it minimizes the air volume that has to be overcome by the pump flow.

yeah - theres another thing that stopped it from working I guess - the length from one side of the "U" internally , to the other . I remember the one I got working before was a moulded , one-piece "U" bend that was off an old plasic pump sprayer or something . This one had too much internal air cavity to work , I'll have to store it and design a massive system with high flow rates to take up the other side of the yard just so I can use that piece and prove to myself that that wasnt a waste of a day , heheh

Agreed Boris, yet it would have worked, if you just made it lower, and allowed the water to cover the top of the pipe by a couple of inches. Siphons a touchy things, but once set up, they'll work forever