Maximum height for a bell siphon?

[germanbull]

I'm testing my first system with a grow bed about 20 inches deep, a 1/2 inch stand pipe 18 inches tall. The bell siphon starts OK, but shuts off with about 6 inches left in the grow bed....meaning, the siphon is not lifting the water more than 12 inches above the water level in the bed. Does anyone have a siphon that is taller than 12 inches?

From what I read, the problem may be with the exit piping. I only have about 3 inches below the grow bed, then an elbow, then another 3 inch horizontal pipe ...all of these are 1/2 inch pvc. The horizontal pipe ends inside a 3 inch master drain pipe.

I'm looking for any suggestions to get the grow bed to drain fully.
Thanks!

[Oliver]

It seems like you are emptying about 2/3 of your water. That should be enough for it to purge your grow bed after a few cycles.

20 inches is deep.

Extending your down pipe will probably help in making it work better. Otherwise, just set you siphon break holes above your lowest water point during the cycle.

Oliver

[urbanfarmer]

I'm testing my first system with a grow bed about 20 inches deep, a 1/2 inch stand pipe 18 inches tall. The bell siphon starts OK, but shuts off with about 6 inches left in the grow bed....meaning, the siphon is not lifting the water more than 12 inches above the water level in the bed. Does anyone have a siphon that is taller than 12 inches?

From what I read, the problem may be with the exit piping. I only have about 3 inches below the grow bed, then an elbow, then another 3 inch horizontal pipe ...all of these are 1/2 inch pvc. The horizontal pipe ends inside a 3 inch master drain pipe.

I'm looking for any suggestions to get the grow bed to drain fully.
Thanks!

What are the inches of the inside and outside pipes and what schedule PVC?

A picture would be good too, to help rule out any other problems. People often think their problem is caused by A when there really might be a B or sometimes even C, D, E, F, G, etc...

[cedarswamp]

I'm testing my first system with a grow bed about 20 inches deep, a 1/2 inch stand pipe 18 inches tall. The bell siphon starts OK, but shuts off with about 6 inches left in the grow bed....meaning, the siphon is not lifting the water more than 12 inches above the water level in the bed. Does anyone have a siphon that is taller than 12 inches?

From what I read, the problem may be with the exit piping. I only have about 3 inches below the grow bed, then an elbow, then another 3 inch horizontal pipe ...all of these are 1/2 inch pvc. The horizontal pipe ends inside a 3 inch master drain pipe.

I'm looking for any suggestions to get the grow bed to drain fully.
Thanks!

Basically what you have happening is the water pressure inside your standpipe and inside of your bell are equalizing because as the water outside of the bell gets lower the positive pressure it creates at the bottom of the outside of your bell gets lower essentially making the water inside of the bell "act" heavier so you need more of a vacuum being pulled by your standpipe to lift it. The way to do that is make your standpipe longer
(the vertical section) and/or larger. Did that make sense to anyone but me?

[davidstcldfl]

Did that make sense to anyone but me?

Actually it did...

[germanbull]

cedarswamp,
Are you saying I could make the standpipe larger, like 3/4 inch, keeping the bell at 2 inches and I would get more vacuum and therefore drain more of the water? I hadn't thought much about the volume of the water being lifted in the bell; I was only thinking of the height of it.

I was going to try Oliver's idea first...to make the down pipe longer, but keep it at 1/2 inch. I didn't try it today because I was letting a sealed leak dry. I'll try it on Thursday and if it doesn't work, come back with the pipe measurements for you all.

[cedarswamp]

Making the drop longer will help but take a look the cross section of your stand pipe vs your bell, 0.19625 inch vs 2.265 inch...you may be better served by a simple loop siphon in your situation

[germanbull]

I made an easy change first by making the drop tube longer...it's longer horizontally, at least. I got pretty much the same result, the siphon stopped with 6 inches of water left in the bed. I then shortened the stand and bell pipes from 18 to about 14 inches and still did not get the siphon to run until empty.

Then I changed the bell pipe from 2 inch to about one and one half inch - still using the 14 inch height....that worked!

I have a couple more combinations to try -- keep the longer drop tube with the taller stand and smaller diameter bell, -- and if that works, go back to the shorter drop tube with tall stand and smaller bell.

[germanbull]

Update on the bell siphon height question.....
As someone suggested, the height wasn't the issue after all. I'm almost certain the problem was I didn't have an air-tight bell. Not being certain of the design, I didn't glue the pvc cap on the 2 inch bell pipe - just slid them together. When I went to try a smaller diameter bell pipe (1 1/2 inch), I didn't have a pvc cap so I just wrapped a rubber glove and rubber band over the top. I worked at the lower height and the taller height.

Now I can move ahead to add the media (I'm using lava rock) and adjust the timing.

On one of my totes, I have a loop siphon made of pvc pipes. I couldn't get it to start reliably with my slow fill rate. I switched it to a hose loop and it worked the first time!