Flinders Biomedical Engineering Equipment Orientation

Medical Flowmeters - Basics
Flinders Biomedical Engineering
A joint department of Flinders Medical Centre
and Flinders University of South Australia, Faculty of Health Sciences
What does it do? Flowmeters measure and control the flow of medical gases such as oxygen, air and nitrous oxide.
Physiology Medical gases such as oxygen, breathing air and nitrous oxide are used in anaesthetic machines,
ventilators, or directly to the patient by means of a breathing mask. Oxygen is used for patients with
breathing problems to increase the level of oxygen into their blood. A mixture of nitrous oxide with
oxygen (entonox) is used for pain relief or relaxing muscles. Medical air and oxygen are used on
ventilators. Oxygen, nitrous oxide and medical air are used on anaesthetic machines. Flow meters are
used in all of these applications
How it works Flowmeters consist of a tapered glass tube containing a ball which floats on the
stream of moving gas. As the gas flow rate increases, the ball is carried further
up the tube, indicating the flow rate. Flowmeters are specifically constructed for
each gas, since the flow rate depends on both the viscosity and density of the
gas. Only the correct tube and ball can be used to repair flowmeters Some Flow
Meters have a dial type gauge to measure flow. Again only the correct gauge
can be used to repair the flowmeter.
Units of measurement Flow : l/min
Typical values 0-15 l/min
Picture of equipment
Flow meter valves
The needle valve is the most common means of controlling gas flow rate. As the valve is opened, the
orifice around the needle becomes larger and flow increases. When closing, the valve must not be
over-tightened - this will drill out the orifice and cause it to leak
Oxygen (White) and Air (Black & White) Flowmeters, Additional “Safety AIR Guard” has been fitted to the Air flowmeter
Orientation pages created and compiled by FBE: mailto:fbe.support@health.sa.gov.au
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