ABSTRACT
Purge flows are low flow rates of either gases or liquids. They usually serve to protect pressure taps from contacting hot or corrosive process fluids or from plugging. They can also protect electrical devices from becoming ignition sources by maintaining a positive inert gas pressure inside their housings or to protect the cleanliness of the optics of analyzers through purging. There is only one type of purge flow regulator that has not been covered in other parts of this reference set: the rotameter-type purge meter. This is the least expensive and most widely used purge meter, and for these reasons it is described in this separate section. The metering needle valves are usually multiple-turn units provided with long stems. The opening around their needle-shaped plugs can approach capillary dimensions.
