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- When filled with sand the float's center of mass is below the water line
- This ensures float stability
- The float is not so short that it is light enough to be pushed around the entrance tank by turbulence
The float is made by gluing caps on the end of a PVC pipe that has been partially filled with sand, or some other type of clean dry fill. A hook is then screwed into the center of the top of the float to serve as an anchor. Rope or some other type of tough string can then tie the float to the end of the lever arm.
Calibration
Once the CD is built it is important to zero the lever arm properly. Do this by draining the entrance tank until it is barely at zero plant flow. This is when the water level in the tank is halfway up the bottom row of holes in the linear flow orifice meter. When the tank is at zero plant flow, just barely lower than the lowest flow rate, adjust the length of the lever arm-to-float rope so that the lever arm is exactly horizontal. After it is leveled, adjust the height of the FC as needed to make sure that there is just barely no alum flowing. Alum should begin to flow with one extra millimeter of driving head from this zero. Tighten the hose clamps to ensure that the FC will remain at its calibrated height.
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