Best size for an Auto Siphon

[Jagungal]

What is the best size for an Auto Siphon using readily available materials ?

I have a bed which is .. umm .. about 300 L I think. I decided that the best size might be a 35 mm outlet so I have run with that. When looking I then found that the designs I have seen have a 35 mm inner, a 70 mm outer and a 100 mm cover. I could not get the 70 mm so with with 90 mm in the outer siphon - and used a funnel in the inner to give it a bit bigger lip. I had seen this in some of Affnan's vids and it seemed a good idea.

For interest only, in the last few days I have been playing with it and the issue was that it worked very well but sometimes cut out early. I ended up finding out that this might have been because of a whirlpool that was being generated. The fix was to put a bend on the outlet -- it now fills .. starts and empties perfectly.

My problem last night was that when I made my cover to protect it from the media, it seems to be too close and might be restricting flows. Although it now empty's ... it seems to gurgle and slow down a lot before the end - and eventually stops before finishing. I have to do a bit more testing tonight - mossies and loss of light caused me to give up.

I then decided to run with a 70 mm inner and forget about the funnel but I just went to a major plumbing supplier. He laughed and told me that 70 mm pipe does not exist. He said there was 80 mm but that I could only get it in 6 meter lengths as it was rarely used.

My other option would be to increase the outer, this guy said 150 mm is available .. but that seems like a bit too much bed space taken up. Might do for now though.

So is 70 mm available ? ... is there something like 120 mm ?, or does someone have designs for auto siphons using commonly available pvc pipe ?.

I am semi considering getting some kind of thick mesh and using that as an auto siphon but I worry that it would not handle the weight of the media pushing against it. Also going to sus out agg pipe.

[GaryD]

Hi Jagungal,

You can get 65mm PVC.......a good size for the bell-syphon....and 90mm or 100mm which is what most people use for the media barrier. (I prefer 100mm because I can get my hand down inside it easier).

The stand-pipe is usually 25mm and the "funnel" is a 50mm - 25mm reducer......which will allow for greater reliability in terms of the flow rates that it will sustain.

I think that Affnan's work around auto-syphons has been excellent. His devices avoid the need for the air tube (which is a prospective point of failure) and they work across a broader flow range.....which is useful for when the flow starts to diminish due to the build up of bio-film.

Gary

[DaveOponic]

I use 40 mm pipe these days from GB's to FT. I used to use 25 mm pipe but find the 40 mm much better because it allows faster flow and never gets blocked with gravel. I use 40 mm tank connector and 40 mm standpipe with 110 mm outer pipe (my hands are big) I am also experimenting with a cap at the bottom of the outer pipe so no gravel can sneak through. It allows me to turn the pipe to break off roots and keep holes clear without any stones slipping through.

Dave

[Jagungal]

Thanks for the tips.

I did get some 65 mm at a different store I went to yesterday arvo, but it does not leave much room around the funnel. I even checked a 25 mm to 50 mm reducer for comparison and as it is pressure pipe, the pipe goes on the inside, meaning the outside is thicker and adds about 3 mm on each side. This does not leave much of a gap using 65 mm. Of course there might be other reducers out there ...

In any case, my siphon is doing better than I thought, I was home last night in the light and did a lot more testing with the close in surround. It does a lot of surging and spluttering as it gets to the last 50 mm, it seems to surge back and forth a bit but in the end it seems to get down to only about 20 mm of water left in the bottom of the tank.

I will do some testing this weekend with gravel in the bed.

Dave - I am using the 32 mm pipe, similar reasons maybe. I was going to use 40 mm but saw that in the AquaponicsWiki site that it might need quite a bit of inflow. It was also interesting that the progression up in sizes and what is needed for an inflow seemed to be geometric rather than a simple arithmetic- in other words, to step up just 8 millimeters in size required a much greater inflow.

110 mm pipe sounds like what I need but does not seem to be available .... I have some other ideas and there is always 150 mm or using 65 mm pipe with a breather tube and no reducer if it becomes an issue..