The phototransistor and the IR LED on this board must have their optical apertures restricted to 1 mm diameter, else the switching point is inconsistent and direction measurement consequently inaccurate. Shrink a 10mm length of 3 mm ID shrink sleeve over each, then trim the shrinksleeve back almost to the face of the device.
The IR LED is the blue device. The phototransistor is of identical form but is transparent. Both these devices have one long lead and one short lead. The short lead is connected the larger mass of metal within each device. The PCB legend shows them installed with one long lead and one short lead. Fit them accordingly, and about 2 mm clear of the board surface so the chopper disk breaks the light path without touching the board.
If the caps used for the housing are the minimum 56 mm internal diameter then the screws used for the downlead connection points must be pan headed, as round heads will foul the pipe section.
