.50 gpm BLFC Button ( Flow Washer ) used in Fleck Valves to regulate the refill rate during Brine Refill.
And if your brine cam gear salt setting goes from 6 - 36 lbs. then you use 0.50 gpm BLFC
For a more information about the difference size BLFC buttons and how they match with difference Brine Cam salt Labels,
see: BLFC button question 0.25 versus 0.50 gpm with Fleck
NOTE: The latest versions are now blue (see alternate photo above)
To REMOVE the BLFC,
This is inside the brass fitting on the side of the Valve Head.
Unscrew the brine tubing
Unscrew the brass fitting from the valve head.
Remove the BLFC Retainer ( pull hard with needle nose pliers ),
to access the "button".
Check the Center Hole for any debris ( piece of sand ).
REPLACING the BLFC Button ---
Numbers "towards" the valve body, or "up" in the BLFC retainer, when inserting back into the Brass Fitting.