The Expressure concept from R. Stahl is a far superior solution to the existing enclosure encapsulation methods for many applications. This concept enables the construction of large yet lightweight Ex d switch cabinets that allow standard electrical and electronic components to be safely used in zone 1. Besides power distribution boards and control systems, Expressure switch cabinets can also house large pieces of equipment, such as transformers or frequency converters, providing reliable explosion protection for everything installed within them.
Pressure relief for zone 1
The PTB- and Dekra-certified Expressure switch cabinet series features a unique pressure relief system. Special stainless steel wire mesh on both sides of the enclosure ensures that the pressure within the enclosure can be reduced effectively, serving as a flameproof barrier that allows for controlled flow of gas combined with heat absorption. If an explosion occurs inside the enclosure, the energy released is absorbed swiftly, safely and effectively. Regardless of where the ignition source is located, only harmless incombustible and non-explosive gas/air mixtures are able to exit the enclosure. The special mesh is also designed to absorb a significant amount of the heat energy that has been generated by the chemical reaction thereby safely lowering the internal pressure within the enclosure. These features effectively reduce the internal pressure in the event of an explosion to a maximum value of less than 1 bar; sparks that might otherwise cause an explosion are safely contained inside the enclosure thanks to the special mesh structure. The maximum surface temperature falls under temperature class T4. Covering the Expressure enclosure‘s pressure relief elements are explosion vent panels with a target pressure of 0.1 bar; these panels seal the enclosure and, under normal operating conditions, offer IP 66 protection.
More capacity, less weight
This innovative, Ex d-certified pressure relief technology offers up to 50 % space and weight savings compared to conventional Ex d solutions. Expressure is a highly efficient, cost-effective alternative to Ex p pressurised enclosures. Moreover, the new protection concept makes it much simpler to install switching and control units in zones 1 and 2, near to the machinery that they control, rather than having to position them far away in a non-hazardous area. R. Stahls‘s Expressure technology comes in a choice of four enclosure sizes, ranging from 300 x 400 x 200 to 1000 x 1400 x 700 mm, and with either a single-leaf door or a double door. With walls just 2 mm thick, these stainless steel enclosures are extraordinarily light, making transportation, handling and installation much easier. Their optimised design also benefits from a smaller footprint. The large, undivided space inside the enclosure provides easy access for installing and wiring switching components and for performing maintenance and inspection work. The volume available within the enclosure for installing equipment is comparable to that of many conventional industrial switch cabinets and control boxes, and allows the switchgear layout used for non-hazardous areas to be used unchanged for hazardous areas without any additional engineering work. Thanks to the futureproof design of the enclosure concept, even last-minute changes to the order can be accommodated with little difficulty at the commissioning and SAT stages. Cable entries can easily be retrofitted at any point in time, and new components can be added to pre-installed equipment. Control elements that have been approved for use with Ex d solutions, e. g. rotary switches, pushbuttons, mushroom buttons, key-operated switches and control lamps, can all be used without modification. Additional accessories include Ex e connection shafts and inspection windows that are available in six different sizes.
Light and easy
In terms of weight and size, as well as the amount of maintenance, conversion and retrofitting work required, Expressure enclosure combinations are often a better choice than conventional Ex d enclosures. The most widely used types of protection are flameproof enclosures. These are usually incredibly bulky structures which are built this way to withstand extreme explosion pressures in the region of 7 to 12 bar. To achieve the necessary pressure resistance properties, very thick walls of 10 to 20 mm are required. Realistically for economic and for technical reasons, this limits the enclosure capacity to not more than around 500 l. Large, complex electrical control panels and distribution boards must therefore be divided between a number of smaller flameproof enclosures. Compliance with the applicable explosion protection requirements complicates the production and installation processes for these flameproof bushings, which are required in order to establish the necessary electrical connections. All joints running through the enclosure wall must be flameproof; this is to ensure that sufficient energy is removed from any flames or hot gases in the area to prevent them from causing an explosion. The encapsulation also makes operation, maintenance and repair more difficult. Any subsequent changes to the internal electrical wiring inevitably require extensive, time-consuming and costly modifications, which must normally be accepted by an explosion protection expert before the equipment can be put back into service. With the advent of the new Expressure technology, complete switchgear assemblies and distribution boards can now be housed in a single enclosure, saving significant amounts of space and cost, and making maintenance a whole lot easier. The amount of planning required is also considerably less. Additionally, components can be retrofitted, modified or replaced quickly and without additional costs.
Spacious without pressurisation
In order to house complex control and distribution systems within an explosion-protected enclosure alongside large-scale equipment and special machinery, solutions using pressurised enclosures (Ex p) have been required to this date. Enclosures with this type of protection have air or an inert gas forced through them. The positive pressure created prevents explosive gases from entering the enclosure. To start operation inside Ex p pressurised enclosures, inert gas must be flushed through the enclosure to force out gas mixtures that have entered from hazardous areas and to create the positive pressure required for operation. This takes time – frequent maintenance, replacement and conversion requires significant down time. However, installing equipment in line with EN 600792 requires various inspections and tests for positive pressure, leakage, test gas supply and pre-flushing time, which makes Ex p structures particularly complex. Compared to this protection concept, the Expressure is by far the more cost-effective alternative. Firstly, it eliminates the need for many expensive design and test steps. Secondly, the Ex protection remains intact at all times – during equipment start-up and after maintenance and retrofitting work – without additional time consuming procedures. And of course, there is no need of equipping Ex p enclosures with a control unit, a feed air station and a pressure monitoring system.
R. Stahl GmbH, Waldenburg
Author: Harald Waskow
Product Manager,
R. Stahl
