Pressure regulators are a subtype of industrial valves designed for automatic upstream or downstream pressure control. A downstream pressure regulator is also called a “reducer valve” or “relief valve,” and an upstream pressure regulator is called an “overflow valve.” Downstream pressure regulators are normally open, and upstream pressure regulators are normally closed. Pressure regulators are distinguished according to the media they handle. There are gas pressure regulators, water pressure regulators, oil pressure regulators and several others. According to their operation principle, they can be spring-loaded, lever type or diaphragm.