A pressure regulator is a valve that automatically cuts off the flow of a liquid or gas at a certain pressure. Regulators are used to allow high-pressure fluid supply lines or tanks to be reduced to safe and/or usable pressures for various applications.

A pressure regulator's primary function is to match the flow of gas through the regulator to the demand for gas placed upon the system. If the load flow decreases, then the regulator flow must decrease also. If the load flow increases, then the regulator flow must increase in order to keep the controlled pressure from decreasing due to a shortage of gas in the pressure system.

A pressure regulator includes a restricting element, a loading element, and a measuring element:

• The restricting element is a type of valve. It can be a globe valve, butterfly valve, poppet valve, or any other type of valve that is capable of operating as a variable restriction to the flow.
• The loading element applies the needed force to the restricting element. It can be any number of things such as a weight, a spring, a piston actuator, or more commonly the diaphragm actuator in combination with a spring.
• When the actuator is forced against an expansion disk, the force is distributed among the pressure walls. This allows the gas to flow at the proper rate and not to be continually vaporized and diluted.
• The measuring element determines when the inlet flow is equal to the outlet flow. The diaphragm is often used as a measuring element because it can also serve as a combine element.