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Safety switch has ATEX dust requirements covered

Edited by the Engineeringtalk editorial team Feb 4, 2004

When rotary valve manufacturer Rota Val was asked to provide a fully tested and certified ATEX version of its flagship Hypergienic valve to a leading pharmaceutical customer, it encountered a problem.

When rotary valve manufacturer Rota Val was asked to provide a fully tested and certified ATEX version of its flagship Hypergienic valve to a leading pharmaceutical customer, the company encountered a problem that machine safety specialist Schmersal was able to solve.

Rota Val of Chippenham in Wiltshire manufactures rotary valves, diverter valves and ancillary equipment for the bulk materials handling industry.

The company's innovative Hypergienic rotary valve range is designed to meet the most stringent hygienic requirements of the pharmaceutical and food industries.

The specific application consists of two units - a top valve that meters material into a cone mill at a particular rate, and a bottom valve that takes material away.

Although the valves are independent of each other they operate simultaneously as a single unit.

Due to the operating environments and the type of materials processed, both valves are designed as explosion/flame containment devices capable of stopping the propagation of an explosion-through flame if it occurs in the line above or below either valve.

As the valves are also designed for CIP installations, access to the fully washable internal surfaces is provided via two removable end covers that slide out on rails.

To ensure that operators and maintenance staff cannot withdraw the end covers while the valves are running, Rota Val engineers specified safety switches from a well-known manufacturer of safety equipment, to indicate if the end covers were being removed.

Due to the potential for explosion in the operating environment, engineers specified switches with ATEX certification to zone 22 (dust).

However, as Rota Val's Contracts Engineer Paul Bailey explains, when the safety position switches were delivered and Rota Val requested formal certification, the safety component manufacturer advised that they were ATEX compliant only for gas.

"We then had to search for a supplier that could provide a dust certificated switch", he says.

"After extensive research, the only company we found that was able to meet the specification was Schmersal".

The unit supplied by Schmersal is a stainless steel EEx 13 safety position switch that is ATEX certified for both gas zones 1 and 2 and dust zones 21 and 22.

On the Hypergienic valve it acts as a positive-break position switch, indicating that the valves are in operation and enabling the safety system to automatically stop the process if the covers are removed.

Summing up Rota Val's experience with ATEX certification, Schmersal Managing Director Terry Hayward comments: "Fortunately we were able to solve the problem.

However, the experience does raise concerns that some safety component equipment manufacturers, may not fully understand the specific and separate requirements for gas and dust environments".