I might be able to help you out. It took me a little while to figure them out... but bell siphons are incredibly reliable once properly set up.
I have had my bells set up for 2 years so far and not a single hiccup. By the way I set them, the plumbing, and the pump up... I am able to go a month without filling the sump tank.
The water level can drop 6 to 10 inches in there... and even with the water flow slowing... the bells still kick on every time without a hitch.
I have a pump set to constant flow. I maximized pump flow by doing a few things.
1st I modified the pump by removing the cover and hard-attached plumbing to it. This greatly increased flow... especially at a higher head height.
2nd I built a cage around the pump to keep large debris from clogging it since things like old leaves kept clogging it every few days and greatly effecting the flow. (siphons too) I found some water planter baskets that had smaller holes than the opening on the impeller for the pump. That way I knew any debris that gets in would flow through. I then punched a hole to route the plumbing through the cage and then zip-tied it shut around the pump. I have NEVER had to adjust my water flow OR clean the pump in the last two years. She has been solid as a rock!
3rd I ran the plumbing to the highest point it will go before doing the split to the different beds. I discovered that doing the split down low... and then raising the water at the different beds... would GREATLY increase the weight of water to lift. Which, cause water flow to drop significantly. Now my pump makes WAY MORE water flow than what is needed. Which enables me to create a pressurized system... which is More Reliable. I just close the ball valve to adjust the flow. When ever
poop and uneaten food gets stuck in the gap in said ball valve... there is
enough pressure to force it through.
After Doing These Things the water flow is now extremely constant. Which is very much needed.
Other than that... I used 1" stand pipes set to 1" below the top of the gravel. Ensuring they have the 90deg bend down below and are extremely vertical. The vertical part is EXTREMELY important. I learned the hard way... that a non-vertical pipe creates a much smaller operating window for the syphon.
For the Bell portion of the pipes. They have to be extremely stable with good water flow. So the entire bottom edge of the pipe is left flat and level to keep it from rocking as much as possible. Floating as you described is going to induce failure. So have the bell tall enough to not float. Other than that it can stick out of the water 20ft if you like. It will still work.
The gravel stand-off pipe just needs to provide good flow. Paying extra attention to the last bit towards the bottom. That way the bed will fully drain before the syphon breaks.
When setting the flow rate for the syphon. Always top off the sump tank to the max first. Making sure to leave room so that air is able to suck back up through the bottom drain pipes to break the syphon. Sounds weird... but it's needed.
Always set the water flow rate so that the syphon has a hard time breaking at the end. Since water flow will only slow down over time due to clogs or water level dropping in the sump tank... this will ensure that the bell syphon
should keep working as long as possible.
If done right... a Bell Syphon has a massive operating window. Which is awesome. At first I was having issues until I figured it out. Let me know if I helped or can do a better job explaining any areas.
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