To fill your Flair 58 using the Valve Plunger (a) Fill brew cylinder to rim with water (b) Raise lever just enough to unseat stem and open valve allowing water to fill head space below (c) Continue to raise lever slowly, and water will pass through the valve and into the brewing chamber (d) Top-off chamber through opening made between stem and plunger once lever is fully raised.
Check out this video for a walk-through of filling with the Valve Plunger, and for alternative methods.
Note that it is important to ensure you are always fully filling the chamber with water, to avoid any air pockets. Air pockets may spontaneously compress and alter the way your plunger travels down through the brew head.
Check out this video for our thoughts and strategies on how to minimize the amount of compressible air in the system, as well as how to properly bleed off pressure at the end of the shot when using the Valve Plunger.