Counteract ignition hazards using overpressure

Ex p systems for controlling pressurised enclosure solutions are essentially based on controller units that monitor the enclosure data and control the supply of inert gases or compressed air via purging valves on the basis of time intervals and pressure values. While conventional systems for a range of control panel sizes and construction types use a wide variety of devices, R. STAHL has reduced this complexity in its new x621 Ex p system to just three basic components in standardised versions. This simple system, consisting of an Ex p control unit, Ex p pressure monitors, which simultaneously also function as pressure outlets, and Ex p purging valves with digital and proportional control, is able to meet all requirements, from very small enclosures with a volume of 10 l to Ex p control panels with volumes of 4000 l.

In this way, the Ex p control unit makes control processes available for all control panel sizes and enables them to be adjusted easily to meet users' requirements. If, for instance, the number of outlets needs to be increased for larger control panels, or if the purging pressure or purging time needs to be reduced, all it takes is the installation of additional Ex p pressure monitors. The use of a suitable number of a single pressure monitor variant reduces expenditure and work for both engineering and storage. The outstanding precision of the sensors enables operation close to the pressure switch-off threshold, which keeps leakage to a minimum and enables extremely cost-effective continuous operation. The purging valve control, which is also integrated in the control unit, further simplifies the process in either digital or proportional mode.

Moreover, effective Ex p vortex air coolers are available for cooling Ex p panels, the cooling power of which can be scaled by installing additional structurally identical versions, in accordance with the same simple principle that applies to pressure monitors. Not least, the Ex p bypass circuit on the control unit, in which the electronics operate intrinsically safely, significantly reduces the required expenditure for inspection and maintenance work. The new commissioning process eliminates the need for costly test steps after maintenance and retrofitting work, and guarantees explosion protection at all times.

The x621 Ex p system, certified as a monitoring system for control panels, is used in Ex Zone 1/21 in accordance with IEC/EN/DIN 60079-2 as a redundant version and in Ex Zone 2/22 as a more cost-effective simple version. The compact design of the components and the state-of-the-art operating interface of the Ex p control unit enable space-saving installation and easy commissioning. The external mounting of the slim control unit on the control panels side walls ensures that the full installation volume of the application is available. The enclosure, which is made of robust, glass fibre reinforced polyester, is available with or without an inspection glass window and can also be protected from heavy rain using a protective collar, which is available as an optional accessory.

To complement its Ex p systems, R. STAHL offers certified Ex p empty panels in ten enclosure sizes, from 400x600x200 mm to 2400x2000x1200 mm. The stainless steel panels are available in single-, double- or triple-door versions; with a wall thickness of just 1.5 to 2 mm, they are particularly lightweight. Thanks to their considerable installation volume, which enables direct transmission of switching system layouts from safe areas to hazardous areas in many cases, and their weight, which has been reduced by up to 80%, these Ex p control panel systems offer an outstandingly cost-effective alternative to Ex d-protected enclosure solutions with a number of advantages.

In this way, the Ex p protection concept makes it easier to install switching and control units close to the machines in Zones 1, 2, 21 and 22, rather than having to position them far away in the non-hazardous area. Unlike Ex d enclosure technology, cable glands can also easily be retrofitted at any point in time, or new components can be added to pre-installed equipment. All control elements that have been approved for use with Ex p or Ex e solutions, e.g. rotary switches, pushbuttons, mushroom buttons, key-operated switches and control lamps, can be used without modification. As an additional benefit, the overpressure inside the panel ensures that the installation remains dust-free, clean and dry at all times, thereby also providing protected areas for delicate switching systems, even in harsh environments.