Backyard Aquaponics
A place to discuss aquaponics

All,
'Hope everyone is doing well... still has jobs and some kind of growth in their 401K.

Hey... a guy in my group has discovered that there is no need for the p-trap part of the drain for the ebb & flow. He sets the stand pipe at the height he wants the water to trigger, places the Bell over the top (no siphon tube), then the drain (beneath the grow bin) is just a straight shot to the tank (or larger drain pipe)... not even an up slope. When the flush ends it allows air to shoot back up the pipe and release the siphon. He says a he gets a complete flush every time.

I suggested to him that all the BYAP peeps wouldn't have designed the p-trap part of the system if it all worked fine without it however I didn't know why; Why his version works as well as he discribes with half the materials and little tweeking. I told him I would ask you all.

I theorize that you need a stronger supply to cause the flush, more than with the p-trap since the p-trap (air-lock) allows a difference in pressure within the Bell and causing an actual trigger when tripped but I may be way off.

Anyway... what is the downside to no p-trap on the drain side of the grow bin.

Thanks for then help.

Tony

Kuda will probably show up later with his diagrams that explain siphon functioning very well but here is my quick take on it.

The simple bell siphon where the water just drops out the bottom of the stand pipe is great if it works with your flow rate. The whole p trap and breather tube additions are for when things don't work right from the start.

If the plain and simple version has trouble starting at the flow rate available and just trickles over at the same rate that the flow enters the bed (leaving you with a continually flooded bed) Then adding the trap on the drain can help. This traps a little air in the siphon causing the water level in the bed to have to go higher before it can push the air bubble out and finally kick in the siphon proper.

Then often when you have a little too fast a flow rate or too long a drop under the bed, you might have trouble getting the siphon to shut off and this is where the whole breather tube comes in to help the siphon get a good gulp of air and stop.

I've found that in a siphon where I have to install the P trap, I then also need a breather tube sine the extra water in the trap can make it difficult for the siphon to get air at the end and stop.

Hi Tony

my autosiphon on one of my growbeds is exactly as youve described - straight pipe , no p-trap

seems to have worked fine for the last year or so since I installed it , I dont see any downside .
After I built it this way I trawled through heaps of posts about bel siphons trying to work out what the little air tube is for and how it works - mine doesnt seem to need it

The trap is to allow the siphon to work with lower flow rates. I can't be bothered doing more diagrams, there's heaps on the other siphon threads. If you wanna see them, do a search.

But as TC said, these additions are to make a siphon not perfectly sized for the system, work flawlessly.
Also recently I have come to see that a big siphon can be made to work on a low flow, so the drain is super fast compared to the fill.

As KP says, the P-Trap increase the range of flow that the siphon can handle.

Hey Guys,
Thanks for the assist. Summary- So the p-trap/siphon tube method makes the system more robust, esp with lower flow rates. I think thats right... right? If the flow rate works without then its OK.

Any known flow rate range?

Thanks again.

Tony

no flow ranges have been documented.
it has to do with not having flow meters and it being difficult to measure flow.

it would be nice if somebody could be bothered

you should check this thread. http://www.backyardaquaponics.com/forum/viewtopic.php?f=8&t=5192&st=0&sk=t&sd=a. I had some bell problems but finally got it resolved with a VERY slow fill rate.

If you look at the diagrams on this site they use a trap to help build up back pressure until the thing "burps" to start the siphon. They also describe how the roof of the pipe is a D shape to encourage a larger burp. The trap on the end of the siphon is there for the same reasons:

http://www.siphons.com/operation.html
(see step 4)

viewtopic.php?p=9153#p9153