Construction attempt #2 was quite the adventure.
I transferred from a “nutrient film technique” circulation system to a split-flow “bell siphon” drainage system, which required several new materials: brand spankin’ new growbeds, all the components required for the bell siphon, and additional plumbing parts for the new configuration. In addition, our tool kit upgraded to include a big fancy drill with all these different bits and attachments and other things I’ve never even heard of before.
The first step of the process was to attach fittings to the grow beds which would hold the standpipe and drainpipe.
Shout out to Dr. Kemp for letting me work on this in the classroom while her biology 580 class was simultaneously dissecting cats about four feet away from where I was working; she also gave me a few tips about how to operate the drill and not bore a giant hole into my own hand. The first growbed ended up slightly cracked, but the second went really smoothly, with secure fittings and no detectable leaks.
Once the fittings were in place, PVC pipe could now be attached to form (1) the standpipe, and (2) the drainpipe. Additional PVC was used to (3) modify the drainpipe and create (4) the media guard.
All the separate components needed for this section required a visit to our school’s theater workshop (“The Shop”), where Mr. Josef and his assistant helped cut the PVC piping to size.
We used 2(1/2)” diameter PVC for the media guard, 2″ diameter PVC for the bell siphon, and 1/2″ PVC for the standpipe and drainpipe. We also cut out a bunch of smaller sections of both the 1/2″ diameter PVC and 1/2″ diameter CPVC to use as part of the plumbing system.
Mr. Josef also provided two planks which were used later on to create a rack across the top of the aquarium to support the growbeds.
I drilled 1/8″ diameter holes to a height of 1″ on a single side of each of the bell siphon pipes, as well as small ‘teeth’ at the very end, and a mixture of 1/4″ and 1/8″ diameter holes for the media guard.
A bell siphon relies on an air tight ‘bell’ over a standpipe. When the water level reaches that of the standpipe, it generates a vacuum within the airtight space, creating active suction that drains the water out of the growbed until the water reaches a certain level (the top-most notch in the bell), at which point air re-enters the bell, the pressure equalizes, and the suction stops. This process is repeated to create a constant fill-drain effect.
Finishing the bell siphon and growth bed construction required lots of minute adjustments.
Factors such as height of the standpipes, suction (determined by drilled holes) of the bell siphon, media guard configuration, drainpipe configuration, and pressure of incoming water flow, all had to be played around with to get the bell siphon to work. It took me over a week, but eventually I had two empty grow beds, each equipped with functioning bell siphons and media guards.