Breathing with a diving tank and filling balloons from an air cylinder both require some way to safely reduce the high pressure inside the tank to a usable level at the exit. Air pressure regulators control the difference in pressure between a high-pressure inlet and a low-pressure exit using springs, diaphragms and valves.
Pressure-Reducing versus Backpressure Regulators
Pressure-reducing regulators hold the pressure leaving the regulator at a specific level. These regulators use the air pressure entering the regulator to push a valve closed. With high pressure entering the regulator, the valve is open only slightly, but as this inlet pressure lowers, the valve is able to open wider and keep the pressure exiting the regulator constant. Backpressure regulators hold the inlet pressure at a specific level. Backpressure regulators use the air pressure entering the regulator to push a valve open, so that air only exits if this inlet pressure climbs above a certain level.
Loading Mechanims Set the Pressure
The controlled pressure, whether exit pressure or inlet pressure, is set with a loading mechanism, such as a spring, that is compressed by turning a wheel or knob. The knob pushes down on the spring, which then pushes down on a sensing element that is in contact with the inlet flow of air. The spring tension controls the flow of air by pushing in opposition to the inlet pressure. Instead of a spring, some regulators use a pressurized gas chamber to provide force to the sensing element.
Sensing Elements Respond to Inlet Pressure
Sensing elements, usually diaphragms, provide both a seal and a physical link between the valve and the loading mechanism. They sense and translate inlet pressure by flexing in one direction or another depending on whether the inlet pressure or the loading force is greater. Diaphragms are made from metal, Teflon or other plastics that can bend without breaking and then return to their original shape as the pressure varies. The specific material used depends on how high the pressure is in a specific application. Other types of sensing elements are pistons and bellows.
Valves Physically Control the Pressure
The loading mechanism pushes on the sensing element, and the sensing element pushes on the valve. The valve increases or decreases the size of an orifice to physically control the amount of air that can pass through the regulator, thereby controlling the pressure. The components of the valve are the stem, poppet and spring. The stem connects the bottom of the sensing element with the top of the poppet, which actually seals the orifice. The spring is on the bottom of the poppet and lets the valve respond to the sensing element in two directions. The spring also returns the orifice to a default position, either open or closed, if something else in the regulator or air pressure system fails.