Figure 9-14 Generic variable-bypass vaporizer. Vaporizer components include the concentration control dial, the bypass chamber, the vaporizing chamber, the filler port, and the filler cap. Using the filler port, the operator fills the vaporizing chamber with liquid anesthetic. The maximum safe fill level is predetermined by the position of the filler port, which is positioned to minimize the chance of overfilling. If a vaporizer is overfilled or tilted, liquid anesthetic can spill into the bypass chamber, causing an overdose. The concentration control dial is a variable restrictor, which can be located in the bypass chamber or the outlet of the vaporizing chamber. The function of the concentration control dial is to regulate the relative flow rates through the bypass and vaporizing chambers. (Modified from Andrews JJ, Brockwell RC: Delivery systems for inhaled anesthetics. In Barash PG, Cullen BF, Stoelting RK [eds]: Clinical Anesthesia, 4th ed. New York, Lippincott-Raven, 2000, pp 567–594.)