March 2007 – Featured Article

ATEX Compliant Rotary Valves

Although Australasian companies are not directly affected by the European ATEX Directives unless they are exporting to the EC, European companies across industry, from equipment suppliers to system designers to end users should now be aware of the ATEX Directives and their implications. Under ATEX 95, manufacturers of components, equipment or protective systems in particular, had to achieve ATEX certification for any new equipment supplied for use in a hazardous dust or gaseous environment by July 1st 2003.

Equipment or Protective System? – There are two fundamental types of ATEX approval for a rotary valves, depending if the valve is simply required to operate safely in a classified area or act as an explosion containment device.

In the first case, the valve needs to be ATEX certified to guarantee that it will not present an ignition source, either electrically or mechanically generated that could initiate an explosion in the environment that it is operating. This environment will have been classified as a particular “Zone” (for example by the user’s own risk assessment or by an independent expert), depending on the frequency of presence of a potentially explosive atmosphere and whether it is a dust or gaseous hazard, or both. The exact valve specification will depend on the zone in which it is certified to operate. These valves are known as “Equipment”.

In the second case, the valve is not only certified as safe to operate within the given zone, but also to act as a safety device in containing an explosion within an area of a system should it occur. Such a valve is known as an “Autonomous Protective System” (APS), and provided it is controlled correctly, it will stop the flame-front of an explosion and preventing it from spreading any further or setting off a secondary explosion further down the system. Many rotary valves are now being specified for this APS purpose. These valves can also be referred to as “Explosion Chokes” or “Flame Blocks”. It should be noted that a rotary valve referred to as “Explosion Proof” or “Pressure Shock Resistant” is not necessarily an APS type valve.

Dust Classes ST1 and ST2. – For a rotary valve to act as an Autonomous Protective System, it has to be suitable for choking an explosion. However different dusts and powders will explode with different degrees of violence, which of course has to be taken into account because a highly explosive dust will explode with greater acceleration of pressure, which is in turn more difficult to choke. Any dust that explodes with an acceleration of up to and including 200 bar/ms is known as an ST1 dust. The explosion front of this type of dust is relatively easy to stop. However, some dusts will explode with greater acceleration of pressure. A dust that will explode at a rate of 201 to 300 bar/ms is known as an ST2 dust. These more explosive dusts are becoming more common as demand increases for products with very fine particle sizes, for example in the pharmaceutical industry. The specification of rotary valve required to act as an APS for an ST2 dust is more advanced than for an ST1 dust, and it is therefore essential that the dust rating is known when the valve is specified.

It Doesn’t Have to be Complex. – A great number of equipment users tend to consider the whole ATEX issue as a highly involved field that they would rather avoid for fear of spending endless hours and vast sums of money addressing. This is often compounded by equipment suppliers who hide behind jargon and try to turn ATEX compliance into a black art (often to hide their own lack of understanding). It really doesn’t have to be that way. DMN, worldwide supplier of rotary, diverter and slide valves, truly understands the issues involved, and is able to relate ATEX to the equipment user’s situation and talk in his language about the implications for the valves required, be they rotary, diverter or slide valves.

Degrees of Certification. – Many equipment suppliers are now claiming to supply ATEX certified equipment, but to what level? In order to achieve certification for Category 3 (Zone 2 Gas / Zone 22 Dust), all that is required is an internal production control system and self-certification. Even for Category 2 (Zone 1 Gas / Zone 21 Dust), a manufacturer can still self certify their equipment provided that a technical file is lodged at a notified body and technical documentation requirements are met.

However, if one considers that the internal chamber of any rotary valve or diverter valve is, by nature, an area where a potentially explosive mix of dust and air can occur frequently, then this implies that Category 1 (Zone 20) will very often apply. ATEX certification for Category 1 requires EC Type Examination and ATEX Quality Assurance Notification conducted by an independent, certified Notified Body. DMN can supply valves that are ATEX certified for Category 1, having worked closely and extensively on valve design with their Notified Body. Furthermore, the range of specifications and rotor designs developed by DMN that are available for Zone 20 internal applications is extensive. The valve performance therefore does not have to be compromised in order to achieve Zone 20 internal ATEX certification.

Regular Service. – Once an ATEX certified valve has been installed into a system, in order to maintain the parameters on which the certification is based, it is important that the valve is serviced regularly. How regularly will depend on the application and the material that the valve is handling. For example it is important that an APS certified valve has the clearances between the valve bore and rotor blades monitored, so that they do not wear to a point where the valve would no longer arrest an explosion. DMN can help to establish a suitable maintenance regime and carry out inspection and maintenance of the valves to ensure that ATEX certification remains valid and complete.

Comprehensive Range. – As a manufacturer at the forefront of supplying valves for ATEX compliance, for several years DMN have been helping their customers to address the sometimes conflicting requirements of valves that perform reliably with the given product and also comply with the demands of ATEX. In that time, extensive experience of the issues involved has been amassed and an extremely comprehensive range of ATEX compliant valves has been built up.

DMN are well known for having one of the most comprehensive ranges of rotary valves, diverter valves and slide valves. As an independent component supplier, unrelated to any other business within the industry, they have been able to work in close collaboration with customers on ATEX. Often these customers are installing systems that can be groundbreaking in terms of ATEX compliance and DMN have developed their products to a point where every valve in the range can now be supplied to an ATEX compliant specification. This includes 13 different ranges of rotary valves and 7 different ranges of diverter valves.

Small Cost, Big Benefit. – So all this impressive ATEX compliance must equate to one thing – extra cost. It is true that the initial investment in both time and money is considerable in achieving ATEX compliance to the extensive degree that DMN has undertaken. However the cost per valve to the user is kept low due to the high volume of valves that DMN is now able to produce in its specialist rotary valve plant in Holland and specialist diverter valve plant in Germany. This means that customers are often pleasantly surprised at how little the additional cost for ATEX compliance is compared to a standard, non-certified valve.

DMN-WESTINGHOUSE has been designing and manufacturing rotary valves, diverter valves and other related components for the bulk solids industry for more than 40 years. Offering tailor made solutions for the mineral, chemical, food, plastics, pharmaceutical and other industries, DMN products are distributed worldwide and are available in Australia, New Zealand and SE Asia through NTR Engineers Pty Ltd., a subsidiary company of Singapore based RAP Engineers.

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