Purge controllers and purge indicators are used to regulate and monitor hazardous environments within enclosures. They control and/or indicate the performance of purging and pressurization systems which supply enclosures with compressed air or inert gas at a specific flow and pressure. Purging and pressurization systems are designed to reduce hazardous gases or ignitable dust within an enclosure to a safe level.
Most purging applications require a minimum enclosure pressure of 0.10 inches of water (inH2O); however, environments with ignitable dust require a minimum enclosure pressure of 0.50 inH2O. Purge controllers and indicators usually attach to enclosures directly and include mounting screws or brackets. Devices with red and green light emitting diodes (LEDs) provide operators with a simple, visual notification of the enclosure’s status. Some purge controllers and indicators can be connected to a programmable logic controller (PLC), distributed control system (DCS), or relay to indicate a loss of pressure.
Specifications for purge controllers and purge indicators include physical dimensions, operating temperature range, purge pressure lower limit, voltage, and casing material. Purge controller and purge indicator dimensions are expressed in English units such as inches (in) and feet (ft), or metric units such as meters (m) and centimeters (cm). Operating temperature range is measured in degrees Fahrenheit or degrees Celsius. Purge pressure lower limit is an important specification to consider when selecting purge controllers and indicators. In addition to inches of water (inH2O), units of measure include: pounds per square inch (psi), kilo pascals (kPa), atmospheres (atm), bars, inches of mercury (inHg), centimeters of mercury (cmHg), feet of water (ftH2O), kilograms per square centimeters (kg / cm2), and ounces per square inch (oz / in2). Choices for voltage include: 12 VDC, 24 VDC, 115 VAC, and 230 VAC. Most purge controllers and indicators use anodized aluminum or stainless steel as the casing material. Purge controllers and purge indicators carry NEMA and/or IP ratings and vary in terms of hazardous area approvals. NEMA enclosures and IP enclosures are designed to house electrical components, protect personnel from accidental injury, and prevent the ingress of environmental contaminants such as dust and water. NEMA enclosures are rated by the National Electrical Manufacturers Association (NEMA), a non-profit organization that recommends safety standards for electrical equipment. IP enclosures comply with Ingress Protection (IP) standards from the International Electrotechnical Commission (IEC). In terms of hazardous area approvals, designations such as class, zone, and group are important parameters to consider. Purge controllers and indicators that are destined for sale in Europe should carry the CE mark to indicate compliance with the ATEX directive from the European Union (EU).