Figure 9-18 Simplified schematic of the Tec 6 desflurane vaporizer. The vaporizer has two independent gas circuits arranged in parallel. The fresh gas circuit is shown in red, and the vapor circuit is shown in white. The fresh gas from the flow meters enters at the fresh gas inlet, passes through a fixed restrictor (R1), and exits at the vaporizer gas outlet. The vapor circuit originates at the desflurane sump, which is electrically heated and thermostatically controlled to 39°C, a temperature well above desflurane's boiling point. The heated sump assembly serves as a reservoir of desflurane vapor. Downstream from the sump is the shut-off valve. After the vaporizer warms up, the shut-off valve fully opens when the concentration control valve is turned to the on position. A pressure-regulating valve located downstream from the shut-off valve downregulates the pressure. The operator controls desflurane output by adjusting the concentration control valve (R2), which is a variable restrictor. (Adapted from Andrews JJ: Operating Principles of the Ohmeda Tec 6 Desflurane Vaporizer: A Collection of Twelve Color Illustrations. Washington, DC, Library of Congress, 1996.)