Siphon Inner pipe size.

[Patrick_L]

Well I got my first GB put together. It’s the bottom of a 1200 litre tote. The GB size is about 350 - 400 litres. The problem I have is that it takes about 10 to 15 min to empty via the bell siphon.

My inner pipe is a ¾ inch or 19mm. is this big enough? Is there a chart for pipe size to GB size ?

Also this is the first time I filled the GB with water and the Hydroton was floating so it could be that there was extra water to drain.

Any help or comments would be greatly appreciated.

Pat

[bunya boy]

Pat,
From posts on this forum and others, 19mm diameter pipe work is the very minimum you should use because of possible flow restrictions due to biofilm build-up and the like.
I have decided to use 25mm diameter PVC as a working minimum, accordingly my auto siphons have a 25mm siphon pipe in a 50mm diameter Bell tube. This empties my 120 litre grow beds (without any media at all, just water) in 5 minutes. 15 minutes for a 300-400 litre GB sounds about right! Why is this length of time a problem?
You can up the size of your siphon tube if you have a 50mm Bell tube, a bit hard if the bell tube is any smaller. Remember to keep the air bleed tube clear and also drill a 3mm diameter hole at the very base of your siphon tube to allow for drainage (very slow, but workable) to empty your GB if the pump supply fails for any reason and the GB hasn't yet siphoned out.

Cheers IanK :D

[Patrick_L]

I wanted to go 25 mm but I was having a hard time finding a 25mm tank adapter so I opted to go with the 19mm. Isn't 15 min to empty a GB too long? How long should it take to fill up? I was under the impression that it needed to empty very quickly?

I've got the small hole drilled in the standpipe :)


Pat

[bunya boy]

Pat,
25mm tank fittings are available from Murray Hallam's website shop here,
http://www.aquaponics.net.au/product/prod68.htm

or at Bunnings in the Garden Irrigation section, don't look for them in the piping section!!! They are not classed as pressure or drainage fittings in Bunnings stock classifications. Murray's are cheaper as well.

15 minutes to empty a grow bed is fine, is doesn't really have to instantly "dump" water from the media, as long as it draws down to expose bacteria on the media and plant roots, to some fresh air for Oxygen absorption. And it depends on how fast or slow the GB fills. The rate required is generally held to be that you should have enough water movement to change the Fish Tank volume once per hour. So even if you have 2 cycles per hour of Flood and Drain, (say 25 minute Flood, 15 minute drain) for your grow bed, you can quite happily have around 1000 litres in your fish tank. Remember that some systems have continuous level Flood, so they never drain at all.
Speed of Drain is only an issue when it comes to the required times for the Flood and Drain cycle/s to complete at least one change of Fish Tank water volume per hour.

Hope this helps,

Cheers IanK :D

[Patrick_L]

I’m in Canada and I guess the local hardware stores don’t carry the 25 mm tank fittings, I will keep looking.

Thanks for clearing up the issue about draining time.

I still want to add 2 more large grow beds to get (my 1:1 ratio 1500 litre fish tank).
With the amount of water needed to fill these grow beds what’s the best way to time things so I don’t run out of water in my fish tank. I’m building a CHOP system. I was going to put a tank fitting half way down my fish tank that way I know I can never take out more then half the water. But I’m concerned that if the timing is off there won’t be enough water (half the fish tank) to get the siphons going in the GB’s.

Pat

[GaryD]

Hi Pat,

They should carry one inch fittings though.........about the same thing.


Gary

[Patrick_L]

I purchased a 1 inch fitting and tried it on a Rubbermaid bin but the connection is no where as solid as a tank fitting.
Scared that in the long run I will have problems like leaking.

[bunya boy]

I still want to add 2 more large grow beds to get (my 1:1 ratio 1500 litre fish tank).
With the amount of water needed to fill these grow beds what’s the best way to time things so I don’t run out of water in my fish tank. I’m building a CHOP system. I was going to put a tank fitting half way down my fish tank that way I know I can never take out more then half the water. But I’m concerned that if the timing is off there won’t be enough water (half the fish tank) to get the siphons going in the GB’s.

Pat, If you are going to use a CHOP system, that implies that there will be constant water volume in your fish tank, the only variation occurs in your sump?
CHOP is Murray's acronym for Constant Height (in Fish Tank!) One Pump (in Sump), so the water level in the fish tank can't change! Others call it a CHIFT PIST, which is an acronym for Constant Height In Fish Tank, Pump In Sump Tank! Same horse, different Jockey!
Your sump needs to carry enough freeboard to accomodate your GB total volume or your need a sequencing valve or similar to lower that sump volume.
With your Fish Tank constant level, gravity feeding your Autosiphons in your Grow Beds, it doesn't matter how the Grow Beds are sequenced, as long as your sump is big enough to hold the volumes.

Cheers IanK :D

[Patrick_L]

Pat, If you are going to use a CHOP system, that implies that there will be constant water volume in your fish tank, the only variation occurs in your sump?
CHOP is Murray's acronym for Constant Height (in Fish Tank!) One Pump (in Sump), so the water level in the fish tank can't change! Others call it a CHIFT PIST, which is an acronym for Constant Height In Fish Tank, Pump In Sump Tank! Same horse, different Jockey!
Your sump needs to carry enough freeboard to accomodate your GB total volume or your need a sequencing valve or similar to lower that sump volume.
With your Fish Tank constant level, gravity feeding your Autosiphons in your Grow Beds, it doesn't matter how the Grow Beds are sequenced, as long as your sump is big enough to hold the volumes.

Cheers IanK :D


I’m doing this inside a greenhouse so my space is very limited. I was going to use a 50 gallon sump with a pump in it. Have it turn on when ever the water reaches a certain level. I was going to try and time things so that one of the 3 main GB’s is always adding water to the fish tank via the sump pump.

My outflow from the fish tank was going to be 2/3 the way up that way if the water drops below that it cant drain the fish tank. I just need to get the timing right.

Think this will work?

Oh also, I found some 1 inch tank adapters, switching everything tomorrow to 1 Inch.

Pat

[Patrick_L]

Well I got the system converted to 1 inch piping yesterday, what a difference. My grow bed now drains in less then a min. This made me have to upgrade my sump pump in the sump to a 1HP pump. This also meant the pipe from the sump to the main is now 1.5 inches. When the pump comes on the water really flows. I’m a little concerned that this may be too violent for the fish. I think I’m going to angle the outflow so that it hits the water at a smaller angle 10 t 15 degrees. This should make the water swirl in the fish tank.

Pat

[GaryD]

Hi Pat,



This should make the water swirl in the fish tank.


.....and this will be good for aeration and will help to concentrate and uneated food in the centre of the tank.....where your fish will eventually eat it (or where you can - and should - remove it if they don't).

Gary

[Patrick_L]

I've been watching my shipon action and i notice that some times the siphon starts before it reached the top of the standpipe. i was thinking this was because maybe my air hose was not big enough.

Should the inner chamber of the siphon clear itself everytime???

I did not have a bigger size clear tube so i added a second tube and cut them both at the same level. hope this helps.

Pat

[Murray]

Maybe it is siphoning via the clear hose....what is the actual flow like. It is a bit odd that it starts before it gets to the top of the standpipe

[Patrick_L]

Well I just spent a couple hours playing with the siphon.

I will do my best to describe what is happening.

When the siphon starts the flow is great, 1 inch (25mm) pipe, it empties the GB (approximately 250- 300 litres) in less then a minute. The problem is when it gets to the end as it nears the air tube the siphon breaks and its make a girgaling sound. As the water in the siphon starts to make its way down back into the grow bed it raises the water and blocks the air tube.
The end result is that the siphon barely has a chance to empty. When I pull on the siphon I can fell a negative pressure pulling back down.

As the water in the GB starts to rise again the water inside the siphon is teetering on the edge of the standpipe. I don’t know what causes it to start again but it will usually start a siphon cycle before the water in the GB reaches the desired height.

Another thing if noticed is that when the water in the GB is on the way up there is a small trickle of water coming out of the outflow pipe into the sump. There is no drip hole in the stand pipe so the water must be going over the edge even thought the level in the GB has not rising to that level yet.

I hope you guys understand what it is I’m trying to say.

I need your help because I not sure how to fix this. Could it be that my air hose is too small?
I’m using a 10mm tube hose. My stand pipe is 25mm and siphon chamber is 75mm

Please help, my plants are dying and I suspect its because they are not getting enough water. :(

Pat

[bunya boy]

Pat,
It would seem to me that there is not enough of a gap between the top of your 1" siphon tube and the top of the bell tube. Try taking a bit off the top of the 1" siphon tube to give you at least 1" between the underside of the bell tube and the top of the siphon tube. Your 10mm (3/8") air bleed is quite big enough and from myour description it is working correctly. It only acts as a "prebreak" not to stop the suction completely. It is the "air gap" at the top of your two pipes that needs increasing so that the siphon can completely break before it starts filling again. I don't think anything would be gained by raising or lowering your supply flow rate. I'm sure if you shorten the inner siphon tube, everything will work OK.

Cheers IanK :D

[bunya boy]

Pat,
I have just re-read your description and noticed that you had a 3" (75mm diam) bell tube. I think this may be a size too big. I think a 2" (50mm) bell tube is better matched to your 1" siphon tube. These are the diameters I am using and everything works O.K. Because we are dealing with volumes here instead of just static head, the larger diameter pipe has a greater volume inside to get rid of before breaking the cycle and because of the extra diameter the depth of head above the siphon pipe is dramatically reduced, thus the trickle.
Consider this; the area of a 75mm diameter pipe is 4418 sq mm and a 50mm diameter pipe is 1964 sqare millimeters. As you can see, increasing the diameter by half increases the area by more than double. The 25mm pipe has a Cross Sectional Area (CSA) of 490 sqmm, so for an equivalent volume of water to be evacuated through it, means a height difference over the siphon pipe of say 10mm for the 75mm pipe and 22.5mm for the 50mm pipe. More than twice the head! All other things being equal. So the 50mm pipe will empty it's smaller residual volume quicker than the 75mm pipe simply because of increased static head and the actual lesser volumes involved, allowing the level to drop completely before the GB inflow takes over to fill the tubes again!
Just a theory, but my 25/50 pipes ratio with the 6mm diameter air break tube, cut about 10mm above the base of the Bell tube, work fine! Gurgles and al!!!

Cheers IanK :D

[cando]

Ian do I get it right that your air tube stops 10mm from the bottom of the outer bell tube? Everyone else seems to stop 50-60mm from the bottom. I only have a protoype of a bell siphon working in a bucket so far and I did think the 50mm from the bottom was too high since there is still a lot of water left in the bucket when the airtube stops the siphon.

Francois

[Outbackozzie]

Another thing to try if the above doesnt work (but it should) is to put an elbow facing up on the drain into the tank. Slows the water flow down, reducing the suction inside the siphon.

[Murray]

You have too much water flow going into the grow bed.
In short, If the siphon won't start there is not enough flow,
If it will not stop there is too much.

Auto siphons often take two or three attempts to stop in fairly close timimg.

What you are describing is typical siphon behaviour that has too much water flow going into the bed

Did you make the auto siphon yourself ?

[bunya boy]

Ian do I get it right that your air tube stops 10mm from the bottom of the outer bell tube? Everyone else seems to stop 50-60mm from the bottom. I only have a protoype of a bell siphon working in a bucket so far and I did think the 50mm from the bottom was too high since there is still a lot of water left in the bucket when the airtube stops the siphon.

Francois
Yep, you got it right, but it's more like 6mm. The difference to my siphon is that it takes a 90 degree bend before going out the end of the grow bed. This means that I still have the depth of the outlet pipe plus the clearance required to fit the tank bulkhead fitting inside the bottom of the Grow Bed; which means about 40mm of water still in the bottom of the grow bed when "empty".
Also in my GB's, because they are "parabolic" in section, the last 40mm depth of water is not a great volume because the section is much smaller than at the top of the GB. Just enough to keep some water in the bed, but not enough to worry about!
You will also notice that the hole saw cut for the bell tube, over the siphon outlet elbow, is cut below centre, meaning that it "clips" over the outlet pipe and doesn't permit it the "float" or rise up for any reason. I thought that was a nifty idea!!

Cheers IanK :D

[Patrick_L]

You have too much water flow going into the grow bed.
In short, If the siphon won't start there is not enough flow,
If it will not stop there is too much.

Auto siphons often take two or three attempts to stop in fairly close timimg.

What you are describing is typical siphon behaviour that has too much water flow going into the bed

Did you make the auto siphon yourself ?

Yes I made it myself. I have made a few now. Today I spent another few hours making and playing with these things. I reduced the size of the bell tube to 50mm and the same thing is still happening.

Murray: The water going into the GB is not very fast, it’s currently taking about 20 to 25 min to fill.

I been watching it closely now for a few days and I have a theory.

The bottom of the outflow pipe leaves the GB and hits a 90 degree turn and then run down a pipe for about 3 feet before falling into the sump. The pipe is on a slight downward angle but I think I can see the potential for water to get temporally suck in the 90 degree turn. Can thin cause problems like this? Maybe it’s keeping the negative pressure going?

Does this make sense?

In the mean time I will try and slow down the water even more.

Pat

[Outbackozzie]

Pat, I can guarantee that your siphon is continuing because of your long drain pipe, angling downhill.

[Patrick_L]

Yep thats what the problem was, water was getting traped. Even my larger 75mm bell works great now.

Thanks.

Pat

[Murray]

I have a fix for that problem.

[Patrick_L]

I have a fix for that problem.

What's the fix? I had to put something together and its not very pretty.

Pat