What is a rotary airlock valve and what does it do?
A rotary airlock valve (also called a rotary valve, feed valve, or dosing valve) is a mechanical device used to meter, control, and isolate the flow of dry bulk materials (powders, granules, pellets) while simultaneously preventing air or gas leakage between two systems operating at different pressures. It consists of a cylindrical housing with a rotating rotor (featuring multiple pockets or vanes) that captures material from the top inlet, carries it around the outside of the housing, and drops it out the bottom outlet. The continuous rotation creates a series of sealed pockets, enabling volumetric or gravimetric feeding while maintaining an airlock between the inlet and outlet chambers.
What is the difference between a 250mm and 300mm rotary airlock valve?
The 250mm (10 inch) designation refers to the nominal pipe size connection diameter, not the rotor diameter. A 250mm rotary valve typically has a rotor diameter of 250mm and a standard inlet/outlet size of 250mm × 250mm (square) or 250mm × 300mm (rectangular). The 250mm size is suitable for material feed rates of 5–20 m³/h depending on rotor speed and material bulk density. The 300mm size (next size up) handles approximately 10–35 m³/h. The selection depends on the required throughput, material characteristics (flowability, abrasiveness, moisture content), and the pressure differential across the valve.
Why use a gear motor instead of a direct-coupled motor?
A gear motor (integral gear reducer + motor) provides several advantages for rotary airlock applications: (1) Adjustable speed — the gear ratio allows precise rotor RPM control (typically 15–60 RPM) for accurate feed rate adjustment, (2) High starting torque — needed to overcome material packing in the rotor pockets, (3) Compact design — integral unit reduces mounting complexity compared to separate motor + coupling + reducer, (4) Smooth operation — the gear reducer provides consistent torque delivery without the vibration of direct-coupled motors. Variable Frequency Drive (VFD) compatibility allows feed rate to be adjusted in real time during process operation.
What materials are used for the rotor in a rotary airlock valve?
Rotor material is selected based on the process material's abrasiveness, corrosiveness, and temperature: SS304 is standard for general dry powders and granules at ambient temperatures. SS316L is used for corrosive materials (salt, certain chemicals) and food-grade applications. Hardox/stellite overlays are applied to the rotor tips and pocket edges for highly abrasive materials like cement, sand, and metal ores. Special coatings (Halar, PTFE, tungsten carbide) are available for sticky or chemically aggressive materials. The rotor can also be fitted with purge ports for pressurized systems.
What pressure differential can a rotary airlock valve handle?
Standard cast iron rotary airlock valves are designed for pressure differentials up to 100 mbar (1.5 PSI) between inlet and outlet chambers. For higher pressure differentials (up to 500 mbar / 7 PSI), a pressurized housing design with labyrinth seals and carbon steel construction is used. For pressures above 500 mbar, a different valve type (e.g., flap valve, screw feeder, or rotary valve with pressure-isolated feed chambers) is more appropriate. Always confirm the pressure differential in your application when requesting a enquiry.
