Backyard Aquaponics
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I'm having some problems with a new bell siphon setup. My other siphons have been working perfectly (shown here: http://www.backyardaquaponics.com/forum/viewtopic.php?f=18&t=5098)

I've made a 3'x5' grow bed. The bottom of the bed tapers towards the center to help drain the water and the standpipe is set in the bottom of the tapered area. The siphon parts are the same as the my others: 1/2" standpipe, 1-1/2" Bell with a fairly slow supply line.

Hopefully I can explain this properly! The siphon has no problems starting, but on the end, you hear the normal gurgle when the water level hits the air brake tube (or intake slots in the bell depending on the tube height) and it *starts* to break the siphon. I believe the problem comes from the stone retaining some of the water so when the siphon breaks, it basically slows down the water from existing a bit, but the water is still coming out of the stone a bit faster and the water level rises, which then air can't get in the tube to finish breaking the siphon. Now there's some extra air in there and it sort of siphons and sort of fills the bed until the level gets to the stand pipe level...then it just dribbles out.

I've tried with no success:
1) Adding some drains channels in the bottom of the GB much, just like my grow troths shown in my other thread. I was hoping that would have drained the stone faster
2) Increased the fill rate
3) Decreased the fill rate

I believe my other siphons work so well since they're external and set far lower than the GB. If I can't fine tune the siphon, I'll probably make one external for this setup too....but was trying to avoid this. Any suggestions would be appreciated!

Try raising your vacume break tube slightly ubtil it works, I had the same problem with my grow bed that has a slightly concaved based.

When I've tried to get siphons to work on things like half barrels cut the long way where the sides or bottom slope (creating a bed that has a variable volume per height) I've had trouble with them. If the flow rate is slow enough for the siphon to cut off, then it is not fast enough to get the siphon to kick in properly. Or if it is fast enough to start the siphon, then it not gonna cut off. I know there are ways to get siphons to work on such beds but I have usually given up.

I hope someone can give you a hand on this. I kinda suspect the external siphon will help you out on this bed since your issue is the bottom of the sloped part is filling faster due to the slope, having the siphon extermal might insulate from that problem by a little bit.

I played with raising this a bit, but didn't want to get too high....I was hoping to drain as much as possible.

I suspected that this may be the problem. The external siphon works really well since it's set so low. I'm also thinking about restricting the flow after the trap a little. If the outflow is slower than the residual flow from the stone, that may do the trick.

You might try turning the bottom of your air tube into a u-shape. So that when it breaks, it's no longer in contact with the water below it. I'm not sure it'll work, but it's probably worth a shot.

Try making the bell pipe housing taller?
I had probs with a siphon not breaking, even using an air line to break it. Since making the housing taller, I don't even need the airline.

Since I inquired about my siphon, it's been running perfectly. I was fighting with it for 3 days before asking my question. I think I'll still make a few adjustments to it...It must be right at the borderline of working. If I breath on it, it would probably stop again!

Deb,
I struggled for weeks to get the system working,...
Your problem is probably that the "Break" tube is filling with water as the level rises in the GB. As the syphon starts it sort of holds the water in the tube making it not work!

Get a sewing needle and poke it through the break tube at its highest point.

This will let it breath and the results will be immediate!!
A pin hole will not be enough to break the syphon ( in fact it will introduce aeration) but will drain the break tube when required!

But won't this defeat the purpose of having a trap? While the water level is slowly rising, the trap needs to be able to "burp" so that the standpipe can get a quick dose of water, starting the siphon action. If there's a pinhole in there, I would think the trap would no longer work properly.

I'm willing to try it and will let you know. Thanks!

Web4, he means to pin prick the small air breather hose.
This hose needs to be able to introduce air easily. If it's full of water and suction keeps it full of water it will serve no purpose.

The trap is for starting, the air hose is for stopping.

Taller bell or shorter standpipe to allow more vortex headroom (stronger siphon pull). Or shorten the air break tube (try the u-bend suggestion first). Siphons always work a little different from when they're first built to when they've got the bacteria slime on them.

Please correct me if I'm wrong, but I think there may be some confusion on how bell siphons may work. Here's a diagram I whipped up to help explain. If there are mistakes, I'll gladly correct them. (I'm hoping the image display properly...I'm not really sure how to embed them in when upload the file to the site!)



1) Start of the process, water level is below the air tube.
2) Water level rises, hit against the air tube, which now creates a "closed" chamber where air can't escape
3) As the water rises, the air pressure increases, the air pressure pushes down on the water in the trap, along with pushing down on the water inside the bell.
4) Once the water level gets low enough in the trap, it can escape (burp)....reducing the air pressure in the bell.....
5)...when it escapes, the water inside the bell will quickly raise do to the decreased air pressure.
6) Eventually, tanks water level will raise above the standpipe level....
7) When it burps, the water level with quickly go above the standpipe and water will start to rush down the standpipe, creating the siphon
8) Siphon created...air pressure in standpipe less than the atmosphere which can suck water through the air tube (but not always)
9) Water still draining...
10) Once the tanks water level is below the air tube, it will suck up air and break the siphon
11) now we're back at step #1

I can understand putting a small U at the bottom of the air tube, to help prevent sucking up water when the level gets low enough to break the siphon.....but I can't understand what a pinhole in the tube will do, since it will not allow the air pressure inside the bell to increase....

problem in step 9 is that there can significant suction to hold water in the breather hose, but insignificant to suck the water out, so the siphon will not break.
What dicko suggests, is a tiny almost insignificant hole in the air tube at the top, to allow trapped water to drain down, and air to flow up (air is easier to move than water but only when the water's out of the way)
Look at your siphon during operation, if the airtube is not empty when the siphon should stop, add a pin prick and your problems will go away.
If your airtube is empty (full of air) when the siphon should stop, and the siphon is still not stopping, you have another problem entirely.

i dont have a trap at the bottom of any of my standpipes and they all syphon ok