Summary
In the bulk solids industry, the terms
powder rotary valve, rotary feeder, and rotary airlock are often used interchangeably, leading to confusion during procurement. While they describe the same piece of equipment, each term emphasizes a different function. This guide clarifies the distinctions so you can communicate precisely with your supplier and ensure you get the right equipment for your pneumatic conveying system.
Defining the Three Terms
This is the broadest technical term. It describes the hardware: a cylindrical housing, a multi-vane rotor, and a drive package.
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Focus: Mechanical construction and geometry.
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Used when discussing: Material of construction (cast iron vs. SS316L), rotor tip clearance, and bearing placement.
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Example: "We need a DN200 rotary valvewith a hard-faced rotor."
2. Rotary Feeder (The Metering Function)
This term emphasizes the valve’s job as a volumetric metering device. It focuses on how much material moves through the system.
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Focus: Capacity, feed rate, and batching accuracy.
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Used when discussing: Cubic meters per hour (m³/h), RPM settings, and fill factors.
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Example: "The rotary feedermust deliver 5 tons per hour of flour to the mixer."
3. Rotary Airlock (The Pressure Function)
This term highlights the valve’s role as a pressure barrier. It is critical in pneumatic conveying where the system pressure differs from the hopper pressure.
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Focus: Pressure differential (dP), air leakage, and system efficiency.
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Used when discussing: 0.5 bar vs. 1.5 bar rating, tip clearance, and blower performance.
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Example: "We need a rotary airlockto prevent blowback into the dust collector hopper."
Comparison Table
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Term
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Primary Function
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Key Metric
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Procurement Context
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Rotary Valve
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Physical isolation and rotation
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Tip Clearance, Material
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"I need a quote for a DN150 valve."
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Rotary Feeder
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Metering and dosing
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m³/h, TPH, Fill Factor
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"My feeder is under-feeding the conveyor."
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Rotary Airlock
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Pressure sealing
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Max dP (bar), Air Leakage
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"My airlock isn't holding pressure; the blower is surging."
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Why the Confusion Exists
In reality, most powder rotary valves perform all three jobs simultaneously.
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A valve mounted under a silo is feedingpowder into a line (Feeder).
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That same valve is lockingthe air pressure inside the pipe (Airlock).
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And it is doing it using a rotating valvemechanism (Valve).
Because of this overlap, manufacturers like Doebritz often combine the terms (e.g., "Rotary Airlock Feeder") to assure the buyer that the unit is designed for both metering and pressure sealing.
How to Specify the Right Unit
When sending an RFQ, use the term that relates to your primary concern, but provide the data that covers all three aspects.
Scenario A: Dust Collector Discharge
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Primary Concern: Airlock (Preventing dust blowback).
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Specify: "Require a Rotary Airlock Valvefor dust collector hopper. Max dP 0.5 bar."
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Secondary Data: Capacity needed (to ensure it acts as a feeder) and material (to ensure the valve survives the environment).
Scenario B: Batching Scale Feeding
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Primary Concern: Feeder (Accuracy).
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Specify: "Require a Rotary Feederfor batching. Capacity 2 m³/h at 20 RPM."
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Secondary Data: Pressure rating (to ensure it can act as an airlock if needed) and voltage.
Industry Jargon
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RAF: Rotary Airlock Feeder (Common abbreviation in the US).
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RDV: Rotary Discharge Valve (Common in mining/heavy industry).
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Powder Feeder: Generic term often used in Food/Pharma.
FAQ
Is a Rotary Airlock more expensive than a standard Rotary Valve?
Not usually. Since nearly all rotary valves are used in some form of pressure system, the "airlock" capability (machined clearances) is often included in the base price of a standard industrial valve.
Can I use a Rotary Feeder for liquids?
No. Rotary valves are strictly for dry bulk solids or high viscosity pastes. For liquids, use a gear pump or diaphragm pump.
Does Doebritz manufacture all three types?
Yes. Doebritz designs equipment that functions as a valve, a feeder, and an airlock. We label them based on the client's primary application (e.g., Sanitary Feeder vs. Heavy Duty Airlock).
Why do some drawings say "Rotary Valve" and others say "Airlock"?
It depends on the engineering discipline. Mechanical engineers often write "Rotary Valve," while Process or Pneumatic Conveying engineers often write "Rotary Airlock" to emphasize the pressure boundary.
Conclusion
While "Rotary Valve," "Rotary Feeder," and "Rotary Airlock" refer to the same machine, understanding the nuance helps you specify the right priorities for your project. Whether you need to meter powder accurately or seal against high pressure, Doebritz provides precision-engineered solutions that satisfy all three definitions.
Need help clarifying your specs?
Contact Doebritz Shanghai Co., Ltd. with your process requirements. We'll help you define the perfect powder rotary valve, feeder, and airlock solution for your plant.
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