ATEX-certified rotary valves
ATEX-certified rotary valves (also known as rotary dispensers) are applied as feeding dispensers for bulk products and airflow-reduction gates in dust extraction systems, central vacuum cleaning systems, pneumatic handling systems, and in similar applications. If certified for compliance with ATEX 95, the rotary valves are approved for use in Ex-zones and as standalone explosion isolation systems.
Depending whether a rotary valve has an ATEX certificate or not and what the ATEX certification scope is, it can belong to one of three types which follow:
- Standard rotary valves which are strictly prohibited from use in Ex-zones or as explosion isolation systems;
- ATEX-certified rotary valves approved for Ex-zones, which are not a hazard of explosive atmosphere ignition if properly rated for the application. This type of rotary valves are strictly prohibited from use as explosion isolation systems;
- ATEX-certified rotary valves approved for operation in Ex-zones and as standalone explosion isolation systems (the rotary valve version is resistant to pressure and/or flame penetration).
The two latter of the three types are often confused with one another when choosing a rotary valve for a specific application. For example, RFQs and technical specifications often state that rotary valves must be ATEX-certified for a specific Ex-zone, e.g. Zone 20 for the protected equipment interior and Zone 22 for the protected equipment exterior. What is not specified in those documents is that the rotary valve will be also operated as a standalone explosion isolation system. The consequence is the purchase and installation of rotary valves with the ratings incompatible with the actual operating conditions. If this causes a need for replacement, it is a difficult and expensive modification. The reasons of those difficulties and costs could be that the original manufacturer has not properly certified rotary valves or the performance of a properly certified rotary valve of the same size is lower than the required minimum (an effect of the restrictions specified in the applicable explosion isolation certificate).
The problem could be solved by purchasing a larger rotary valve. However, this may require system modifications which can be rather expensive.
In some applications, it is better to use another solution: install a HRD explosion isolation system instead of replacing the rotary valve. In most situations, the solution does not require a larger installation space and can be installed directly on the existing ductwork or material transfer unit (downstream of the rotary valve).
As every explosion protection system, ATEX-certified rotary valve requires regular service inspections. In this case, manufacturers usually specify the maximum service inspection intervals in the product technical documentation with a claim that the actual service inspection frequency depends on the operating conditions and must be determined with the operating experience of the installation user.
In practical terms, certain operating conditions require a service inspection several times a year to avoid invalidation of the ATEX certificate (which applies to a specified maximum gap between the rotor blade edge and the rotary valve body).
- ATEX 95 certificate for Zone 22 and 21 outside the rotary valve and Zone 22, 21 and 20 inside the rotary valve;
- Certified explosion isolation system: the rotary valve stops the flame wave and resists the impact of (reduced) explosion pressure at:
- 1.14 barg (model S-AX);
- 1.4 barg (model H-ARP);
- 10 barg (model H-AR);
- Connection port flange size: DN 150 to DN 500;
- Connection port flange form: round to round or round to square;
- Material(s): cast iron; stainless steel; optionally finished with coatings resistant to abrasion, corrosion and/or high temperature;
- Max. throughput: 180 m3/h (at 100% efficiency and 1kg/dm3 bulk weight);
- Max. operating differential pressure (inlet to outlet): 1.5 bar;
- Dust-sealed bearings, installed on the valve exterior.
- Selection of optimized unit;
- Delivery and installation;
- Inspection and servicing.