bendover -vs- bell siphon

[opihiman911]

I am in the process of building a simple 3x7' grow bed. My original design was to have a 1" drain exit out the end cap of the grow bed and use a bendover siphon using the 1" pvc pipe build in an upside down U fashion with an 1 1/2"-2" mouthpiece to suck up water from the bottom of the bed. I chose this design because I've seen a couple in action locally and they seemed simple to create and maintain.
Well after finding this site I learned about the bell siphon design, but never seen one in action. One thing that I noticed is that all the pics I've seen of bell siphons, they have the drain coming out of the bottom of the bed. Can I adapt this to exit out the side? or will I have to hang the grow bed 6" off the edge of the table or drill an exit hole in the table to allow for the bottom drain pipes?
What are the pros and cons between these 2 siphon systems. Which one would be the simplest most foolproof design for a simple first time small growbed. Any other simple siphon design that are made from parts available from Ace or Home Depot (minus the bulkheads which I already had a couple 1" fitting laying around).
I was also wondering about PVC pond liners. I have been unable to find a local source for the tougher EPDM liner so I had to settle with black PVC pond liner available at Home Depot. It came in 15' width so there in enough to do 2 grow beds of my current size, or will it help in durability if I double up the liner for the grow beds? As far a grow medium, I have a choice of heavy pea gravel or sharp black lava cinders, no nice round lightweight hydroton available here.
Thanks for the help.


Peace,
Cory

[bunya boy]

One thing that I noticed is that all the pics I've seen of bell siphons, they have the drain coming out of the bottom of the bed. Can I adapt this to exit out the side? or will I have to hang the grow bed 6" off the edge of the table or drill an exit hole in the table to allow for the bottom drain pipes?

Opi,
Have a look at the drawings for my system (search for "Bunya Boy")which use a side exit from a bell siphon, and through pond liner, it works fine.
Picture below.
Cheers IanK :D

[GaryD]

Hi Opi,

Matt and Shannida Herbert use something similar to what you've described. You'll be able to see one at work in the second of the videos that they offer......here (http://www.aquaponics.com.au/aquaponics_videos.htm). Their U-type auto-syphons have been going for years.

Auto-syphons are good......the only thing better (in my opinion) is no auto-syphons...... continuous flow. I like just about everything about auto-syphons......but continuous flow is even less problematic.

Gary

[opihiman911]

Hi Opi,

Auto-syphons are good......the only thing better (in my opinion) is no auto-syphons...... continuous flow. I like just about everything about auto-syphons......but continuous flow is even less problematic.

Gary


I originally thought about a continous flow system and designed a basic overflow drain that was a couple inches below the top of the the gravel. It seemed the most basic foolproof method to me.
When I showed it to the only another aquaponic person I know locally, she said it would work, but you don't drain the bottom of the tank and will end up with "stagnate" stale water on the bottom, especially if you just pour the inflow water on top of the grow bed. She said the only way this would effectively circulate the grow bed water is if you pump the inflow from the bottom instead of spilling on top of the bed. Fact or fiction?

I like the bell siphon system especially now I know I can use it with a side drain.

Peace,
Cory

[opihiman911]

I went and watched that second video that you posted: http://www.aquaponics.com.au/aquaponics_videos.htm and have a couple questions.
It looks like they had the inflow of the drain up near the surface right at the same level as the U bend. To me this looks more like a continous overflow drain. How does it create a spihon if the inflow is out of the water near to U bend?
The bendover siphon I've seen ends on the downleg of the U bend and ends about an inch or two from the bottom of the bed and ends with a 2" widemouth adapter. The water fills up past the U bend, forces water past the U bend into the exit downleg and creates an exit siphon and drains the bed down to an inch or two till the widemouth adapter at the bottom hits air and breaks the siphon.
Am I missing something?

Peace,
Cory

[Bidadisndat]

Cory, I think that there are actually two separate fittings that you are looking at: One is the syphon, which does indeed finish near the bottom of the GB as you described, and the other is simply an overflow pipe to carry off excess water, such as you would get when it rains. By using a 'T' piece, you could actually have a syphon and an overflow standpipe use the same pipe that would run through the side of your GB, making it unnecessary to have another bulkhead fitting.
As for the other point, your other aquaponics person is quite correct: If the inlet to your GB is at the same level as the outlet at the top, the incoming water will simply flow along the top and out, and the water below will stagnate.
I guess it comes down to personal preference, but I go with the flood and drain concept rather than continuous flow, simply because when the GB floods, 'stale' air is pushed out by the rising water of the flood phase, and fresh air is drawn in by the falling water of the drain phase.

Cheers,

......Bid...

[bunya boy]

Here's a section showing how my side exit from the auto-siphon works plus the top inlet and overflow going back to a common drain stack.
It works fine.
Note that the media shroud for the bell siphon only has hole at the base of the GB to ensure that water is delivered at the top, but can only drain from the base!.

Cheers IanK :D

[opihiman911]

and the other is simply an overflow pipe to carry off excess water, such as you would get when it rains. By using a 'T' piece, you could actually have a syphon and an overflow standpipe use the same pipe that would run through the side of your GB, making it unnecessary to have another bulkhead fitting.
......Bid...

Bid, I am trying to picture this T-piece design. If one end of the T went to the bell siphon and the other end went to an overflow pipe that was say 1/2" above the bell siphon open to the air, wouldn't that let air into the system and break the siphon?
I had planned on just using a second bulkhead to add an overflow drain as bunyaboy show in his schematic. I wasn't sure though if the overflow drain should drain off to the ground as when it rains and adds water, or should it flow back into the FT in case the bell siphon malfunctions and the FT won't go dry from overpumping. I'm leaning toward back into the FT because I'm more worried about siphon malfunction and draining the fish tank. It is really hot, dry, not much rain on my side of the island so any rain overflows would be far and few between.

Peace,
Cory

[Bidadisndat]

Not if the T fitting/overflow standpipe is placed between the syphon and the bulkhead fitting. As the syphon is operating, water being drained out will probably suck some air down the overflow due to the venturi effect, however the water flowing out will take any air bubbles with it. (And if the water is draining back into your FT rather than a sump, that's not a bad thing.)

......Bid...

[opihiman911]

Not if the T fitting/overflow standpipe is placed between the syphon and the bulkhead fitting.
......Bid...

Okay, I think I have a grasp on this now.
It would have to be assembled in order of bulkhead fitting, piece of pvc, T piece going up to overfill pipe that is 1" above the U bend, another piece of pvc with an elbow that goes up and makes a U bend, then a downpipe that goes into a 2" adapter and ends an inch or two from the bottom.
I think I will go with the bendover siphon now since I know it works right off the bat and I have all of the pieces laying around the house. Bell siphon can be another project once I get it up and running.
I wish there was an easier way to freehand draw pictures and diagrahms on these boards. I am so much better at visualizing things. Give me a picture or schematic and I can make it right the first time. Try and explain it to me I will have to ask you a dozen questions and still probally get it wrong. A picture saves me a hundred do overs all the time.
Thanks for the help Bid, but I may still have another 11 questions to go :D

Peace,
Cory

[GaryD]

Hi Cory,



As for the other point, your other aquaponics person is quite correct: If the inlet to your GB is at the same level as the outlet at the top, the incoming water will simply flow along the top and out, and the water below will stagnate.


She might be correct if the water level in the grow bed was only a couple of inches below the surface......but the water level is actually much lower than that.

Continuous flow might not be an option for you anyway since continuous flow, as I use it, relies on the expanded clay taking up the water (by capillary action) for several inches above the actual water level. I'm not sure that the cinder material to which you've referred would behave in the same way. Gravel, for example, does not hydrate to the same extent as clay pebbles.

Of course, if your growing media was not so deep......say only 150mm (6" deep) you might be able to tune the whole thing so that it would work on continuous flow. The name of the game is for the plant roots to access moisture without its crown being immersed in water.

While the flood and drain action does draw air down through the beds, this is not going to be a huge issue in a continuous flow set up (like mine) because the clay pebbles have a large air void.


Am I missing something?

Bid was right. There are two fittings......one of which is an overflow. While you could design things so that you only used one fitting, I'm inclined to think that the separate overflow was a failsafe measure where, in the event that you got a blockage in the auto-syphon, you wouldn't end up pumping the whole system dry.

Gary

[Bidadisndat]

Cory, you've got it right with your description. I too wish there was an easy way to post sketches. (Well, there probably is, but you and I just don't know how to do it. :()

As for the bell-syphon V the inverted U-tube: As they both work it's six of one and half a dozen of the other, though the bell-syphon doesn't seem to take up as much space, and as its manner of operation is not obvious to the beholder you can use it to mystify guests. (Ha! As if keen aquaponicists are going to keep all those dark secrets to themselves, lol.) If you've got a chance sometime, how about dropping into the Lounge forum and telling us if you've got any other self-sufficiency tactics going or plans in mind.

Thanks Gary, your post just answered an unasked question of mine regarding continuous flow. I didn't realise that with CF systems the water level was much lower than FAD systems, and relied on capillary movement of water up through the growing medium.
The cinder material Cory is talking about is something like scoria, or coarse pumice stone. Plenty of that in Hawaii - and they occasionally make more. :D



......Bid...

[GaryD]

Hi Bid,


I didn't realise that with CF systems the water level was much lower than FAD systems, and relied on capillary movement of water up through the growing medium.
The water level in my 300mm growbeds is about 40mm.

Gary

[Bidadisndat]

The water over my regular 30cm garden beds has been 40cm at times.
(Been flooded out five times in four years. :( )

[GaryD]

Hi Bid,

We're fortunate in that we live on a sloping block.....and we're well above the 1974 flood level. While that doesn't mean that we'll never have flooded grow beds, we do know with certainty who/what was responsible....us.

Gary