A regulator reduces high pressure gas down to a lower useable pressure (normally about 400 kPa) and keeps the pressure constant.

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. Regulators are used in all of these applications..

As gas flows out of the low-pressure chamber, the drop in pressure reduces the force generated by the diaphragm against the spring , allowing the valve to open and admit gas from the high-pressure chamber. The output pressure may be adjusted by a screw that alters the force applied by the spring. Most medical regulators produce a higher output as the supply pressure drops.  Regulators can be built to have a double stage pressure reduction to improve regulation.

Warning: Never lubricate oxygen regulators with oil or grease. Always use oxygen compatible lubricant, pressure gauges and oxygen compatible thread tape. Oil/grease when mixed together with high pressure oxygen is very explosive.