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Re: [APD] The siphon saga continues...need safety shutoff!

Wait... I think there is some confusion in this discussion. I think you are 
under the impression that they are using an overflow siphon without a skimmer 
box... I don't think they are doing that (or at least that's not how I 
interpreted their message).  If they ARE doing that they are just asking for 
trouble... thats a completely uncontrolled siphon. Without a skimmer box it is 
possible for the siphon to siphon faster than the pump pumps, and it will 
continue to siphon when the pump is turned off. In fact, it would be very 
tricky to set something up like that because you would have to make sure the 
flow rate is the same as the pump. That being said, I really don't think that 
is what they are trying to do... I imagine they are using a skimmer box just 
like everybody else. 

I think their main problem with bubbles is caused by a combination of 
outgassing and turbulence. 

1) Outgassign:  He mentioned the pearling because that means the water is 
saturated with O2... that means it is possible for bubbles to form inside the 
skimmer box (outgassing). He doesnt necessarily mean those bubbles from the 
plants are getting into the siphon tube. 

2) Turbulence: When the water falls into the siphon box sometimes there is 
some turbulence that can cause bubbles to get pushed into the siphon tube. 

Outgassing is particularly a problem if you have a second siphon that doesnt 
have a continuous flow (as suggested earlier). Eventually the water will 
outgass and create bubbles in the top, possibly enough to break the siphon. 

Next, the issue of evaporation doesnt have anything to do with the outside 
overflow box... it has to do with the inside box. If you want to have a siphon 
that doesnt siphon until the water level rises (the main siphon fails), you 
have to put a tube around it keeping it from siphoning until the water rises 
above the level of that tube. Below is a picture

   |  |      |  |
   |  |      |  | 
   |  |      |  | 
   |  |    | |  | |
   |  |    | |  | | 
~~~|  |~~~~|~|  |~|~~~~~~
   |  |    | |  | | --------> the water inside this tube will evaporate
           |      |           and break the siphon.

Someone mentioned before that it would replenish itself from the outside box, 
this is impossible because the water level on the outside box must be lower 
than this level in order for the other one to siphon. Thus water cannot move 
from the outside box to the inside box. No matter what, you are going to have 
evaporation problems and outgassing problems with a non moving siphon.

Quoting Laura Burbage <leuhrich at yahoo_com>:

> If I remember correctly, the air was getting into the
> siphon because the plants were pearling a lot, no?  If
> this is the case, then the part of the skimmer box
> that resides _inside_ the tank will keep out the
> bubbles.  The bubbles would go around it, and break at
> the water surface, while surface water overflows into
> the skimmer box.  Even if a few bubbles did get into
> the skimmer box, they would still stay at the top (and
> break), while the intake for the siphon is a few
> inches lower.  The inside skimmer box is also what
> keeps your tank from draining if the pump should stop
> (the water level falls below the top surface of the
> box and ceases to drain into it).  Oh! and a really
> good point that I didn't think of was that both
> siphons could drain to the same outside overflow box,
> preventing water from evaporating from it. If the
> second inside skimmer box is higher than the first,
> the siphon will just sit there on call until needed.
> OK, really primitive drawing below to show the path of
> the bubbles that are currently getting in the siphon.
> -Laura
>               siphon
>           ______________
>    inside | __________  |
>       box | |         | |
> ~~~:~~~|~~| |~~|~! |  | |      |
>    : . |  | |  | ! |  | |      |
>       .|_______| ! |~~| |~| |~~|
>         . .      ! |  | | | |  | outside overflow box
>  tank      :     ! |______| |__|
>            :     !        | |
>            :     !        | |
>         bubbles  !        to sump
>            :     !
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