A rotary valve (often called a rotary airlock) fitted under a dust collector hopper, controls how collected dust is discharged while helping the filtration system hold its designed pressure balance. For South African sites running baghouses or cartridge collectors, the right rotary valve improves airflow stability, reduces housekeeping issues and can support safer operation where combustible dust is present.
What a rotary valve does
Rotary valves meter dust from the collector into a bin, screw conveyor or pneumatic conveying line while maintaining a seal between two different pressure conditions. This as a common solution when discharging from a filter or cyclone to a silo at atmospheric pressure, and the rubber blades/seals provide an effective air lock between the inlet and outlet. A good airlock limits “false air” ingress, helping the fan maintain steady negative pressure and consistent filtration performance.
Selection basics: match the valve to your dust and duty
Key limits when choosing a Nederman rotary valve:
- Particle size: NRSZ3 is intended for particles up to 3 × 3 × 10 mm; larger NRS/NRSZ valves allow particles up to 13 × 13 × 13 mm.
- Abrasion: the NRSZ type is not recommended for highly abrasive dust.
- Loading: for the NRSZ range, it is advised operating at no more than 60% of maximum capacity to help preserve the sealing function.
Nederman also lists typical industrial protection (IP55) and operating temperatures around -20 °C to +40 °C for these valves which is useful when specifying equipment for indoor plant rooms or exposed outdoor installations.
ATEX rotary valves: where discharge meets explosion protection
ATEX Directive 2014/34/EU sets EU rules for equipment and protective systems intended for use in potentially explosive atmospheres. In dust handling, hazardous areas are commonly classed as Zone 20 / Zone 21 / Zone 22 depending on how often a combustible dust cloud is present.
In South Africa, hazardous-area projects also reference SANS 60079-10-2 for dust area classification work, including the preparation and review of classification drawings.
For combustible dust applications, Nederman’s ATEX-certified NRSZ rotary valves are certified for explosive dusts St1 and St2 and as a protective system according to ATEX definition. Typical Kst limits of up to 200 bar·m/s (St1) and up to 300 bar·m/s (St2). The NRSZ3 ATEX version is designed to be explosion pressure shock resistant and to prevent transmission of explosion effects (pressure wave, flame and sparks) up to the specified reduced explosion pressure (Pred), and it specifies that the rotary valve must be stopped automatically and instantaneously in an explosion event.
In other words: an ATEX rotary valve is not a generic label, but certification plus correct system integration (controls, interlocks and duty limits) must match the real dust risk and installation zone.
Envirox: specialists in dust filtration solutions
Envirox supports South African operations with end-to-end dust filtration solutions, including hopper discharge engineering and rotary valve selection. Whether you need a standard airlock for process stability or an ATEX-certified rotary valve for combustible dust risk management, Envirox helps match the valve, controls and installation details to your real duty conditions.
