Siphon Physics - Bell Heights and Drain Lengths

I have done some work on the bell siphon, and determined some interesting things:

The height of the bell does NOT seem to matter for siphon start.

To test this, I used a bell that was literally twice the length of the original, so that there was a very large air-column present.  Not only did the siphon start on schedule, but it also burped just as the original bell had.  I'd like to see this happen with a transparent bell, so as to see where the water level sits during operation.

Note that a siphon can operate with a gap between the drain and the supply; this is a "drip siphon."  It may be likely that any sufficiently large bell will always contain residual air during operation.  Whether or not this impacts the drain rate has not yet been determined.

Drain length DOES determine siphon rate.

To test, I ran a cycle with a short drain, then lengthened the drain pipe significantly.  The drain was a straight drop, down to a couple of 90-degree bends for back-pressure.  I stopped filling the basin once the water started spilling over.  While I have yet to go back over the videos and time the actual drains, I believe the longer pipe does in fact contribute faster drain rate. 

UPDATE: I determined from watching my videos that the short drain test emptied in approximate 61 seconds, whereas the long drain test emptied in approximately 47 seconds.  I timed from when the water started spilling over to when the bell finally burped.  According to calculations, the best possible increase in drain rate should have resulted in a 20-second decrease in drain time; I achieved 14 seconds decrease in drain time.  
I suspect the other 6 seconds may be due to lack of sufficient intake (I have perhaps 0.9 square inches of intake area available, turbulence notwithstanding), coupled with flow restrictions from the double-90's, and the reduced flow area inside the bell where the reducer is located.  Also, the imperfect seal between the bell tube and dome allows for air to intrude, and may be weakening the siphon rate.  A more careful examination of these variables will be required.

The math backs this up: according to Bernoulli's equations, the length of the drain pipe alone determines the siphon rate - up to the maximum possible rate, which is determined by another portion of the siphon and associated pressures and densities.  As such, doubling the drain's length will increase the siphon rate by a factor of roughly 1.4.  Example:  A 5" long drain on a siphon made with 3/4" pipe will drain at 449 cm3/sec.  That siphon with a 10" drain will operate at 635 cm3/sec, other factors notwithstanding.

The lesson should be clear: maximize the length of your drain pipe.

Snorkel Test #1

I also built a basic snorkel and tested it.  One interesting thing to note: the water level in the snorkel never went higher than what I would suppose to be the level of the water in the siphon itself.  Once the snorkel finally received air, the water was sucked up into the top of the bell and the siphon was broken.

I assembled my snorkel from a 3" to 2" reducer, then a 2" to 1", which I further reduced to 1/2" and then made two 90-degree turns.  To this I screwed in a pipe barb and attached a piece of 1/4" vinyl tubing.  The tubing is not yet secured to the bell.  I am anxious to try the inverted cup method, and would like to see how it operates with the cup attached to the side of the siphon.  I would also be curious to see if 1/2" PVC could be used instead of the vinyl tubing.