Automated Chemical Doser Design

The automated chemical doser (ACD) has three principle components: a float, a lever arm, and a flow controller (FCM).

The float currently used in the lab for data collection is a 45.5 cm long 4 in PVC tube capped at both ends and partially filled with sand so that it weighs 8 lbs. It rests 33.5 cm below and 12 cm above the water line in a virtual grit chamber, which is a deep bucket with a pressure sensor at its base. This pressure sensor provides readings of the water level in the bucket.

The float is connected via low-elasticity fishing line to the lever arm. The lever arm is a 68 cm length of 1 1/4 in schedule 40 PVC pipe with a pivot point at 34 cm (the center). Opposite of the pivot there are notches cut into the pipe at 5 cm length intervals. The chemical doser hangs from these notches.
A 1 1/2 in schedule 40 PVC pipe attached to a flange base holds up the lever arm.

The top of the pipe is cut in a saddle shape to fit the lever arm through it and create the pivot. The height of this base pipe depends on the design constraints of the plant it will be built for.

The chemical dosing tube is a tube with an open T connection at the top, which allows the FCM outflow tubing to drain through a pressure break T. The tubing exiting the pressure break T has a larger diameter than the tubing entering it. The pressure break prevents liquid in the dosing tube from backing up when dosing levels change, and the two different sized tubes prevent the T from flooding. Currently ¼ inch outer diameter tubing is used to connect the flow controller to the pressure break T, but it is not known what size tubing is necessary to prevent flooding in the T. Experience has indicated that ½ inch inner diameter tubing is large enough, but it is possible that tubing with an inner diameter as small as 3/8 inch could work as well.

For laboratory testing, water flows from the bottom of the chemical dosing tube to a plastic column with a pressure sensor at the bottom. This pressure sensor gives readings of water height in the column, which can be converted into flowrates from the FCM.