Which of the following automatic feed systems are used to regulate water levels when using a humidifier with a continuous feed system?

1. Leveling reservoirs
2. Flotation controls
3. Optical sensors
a. 2 and 3 only
b. 1 and 2 only
c. 1, 2, and 3
d. 1 and 3 only

ANS: C
The simplest type of automatic feed system is the level-compensated reservoir (Figure 38-7). In these systems, an external reservoir is aligned horizontally with the humidifier, maintaining rela-tively consistent water levels between the reservoir and the humidifier chamber. In flotation-type systems, a float rises and falls with the water level. As the water level falls below a preset value, the float opens the feed valve; as the water rises back to the set fill level, the float closes the feed valve. An optical sensor can also be used to sense water level, driving a solenoid valve to allow refilling of the humidifier reservoir.