A vaporizer for vaporizing a liquid anaesthetic has an inlet for a carrier
gas, an outlet for the carrier gas and vaporized anaesthetic, a flow
channel connecting the inlet to the outlet, a chamber for liquid
anaesthetic, a first connection between the flow channel and the chamber,
a second connection between the flow channel and the chamber downstream
from the first connection and a throttle in the flow channel between the
first connection and the second connection. The second connection has a
conduit, one end of which is immersed in the liquid anaesthetic, and a
valve connected to the other end of the conduit so as to increase safety,
prevent leakage and erroneous dispensing and allow the use of liquid
anaesthetics with a low boiling point. The valve is devised to open when
there is a predetermined drop in pressure across the throttle, allowing
liquid anaesthetic to be dispensed into the flow channel.