Flowmeters are used to assess the flow rate of gases that pass through them. These delicate instruments are always calibrated for one gas only in an anesthetic system.

The flowmeter system consists of a control valve and flow meter sub-assembly. A needle valve is used as the control value and is responsible for controlling the flow of gas passing through the flow meter. Aggressive handling of these instruments can lead to breakage or false readings. Thus, flow meters should always be operated by hand and with care.