Introduction — What is a Rotary Valve and When to Use It
The rotary valve (rotary valve; airlock) is process equipment for handling powders and granules: the cell rotor transfers product from one point to another, controlling flow rate and often acting as a pressure barrier (airlock) between zones at different pressures. In pharmaceutical lines, it is used in phases such as: silo/IBC discharge, feeding mills and mixers, pneumatic conveying, dosing to presses and encapsulation machines.
When to use it:
- For controlled discharge (gravimetric or pneumatically assisted) of powders/granules.
- For pressure isolation in pneumatic conveying systems (dilute/dense phase) or between zones with ΔP.
- For repeatable dosing, when control via rotor speed ensures stable flow.
- To prevent air/gas backflow, preserving downstream process integrity.
In pharmaceuticals, the selection requires attention to sanitation, cleaning and documentation (cGMP), compliant materials and finishes (FDA, USP Class VI), quick disassembly for cleaning, and CIP/SIP capability where applicable.
How It Works — Principles (Rotor, Seal, Flow Rate)
The valve comprises a body with inlet and outlet and a rotor with cavities (cells). The product, by gravity (or entrained by air in the blow-through type), fills the cells in the upper part and is discharged at the bottom as the rotor turns.
Key principles:
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Seal/airlock: Proper clearances between blade tips and body minimize air bypass and ensure pressure isolation.
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Flow rate: Proportional to volume per revolution (cell geometry) × rotation speed.
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Shear and product integrity: Rotor geometry and material influence handling delicacy, reducing degradation of fragile particles.
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Cleaning and disassembly: In pharma environments, sanitary and dismountable design is essential to avoid dead zones and facilitate cleaning/inspection.
Common configurations:
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Drop-through (gravity discharge): Product falls through the valve; used as feeder/isolator.
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Blow-through: Blades discharge directly into a pneumatic line; improves pick-up and reduces accumulation.
Types of Rotary Valves for Solids
By Function and Rotor Geometry
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Straight vane rotor (multi-cell): Most common for general airlock/feeding.
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Scalloped/rounded rotor: Reduces retention and shear on delicate particles.
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Rotor with flexible tips (e.g., PTFE): Compensates for small tolerances, improves sealing with low abrasion.
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Dosing rotor (low volume/micro-dosing): Reduced cavities for fine and repeatable dosing (natural synergy with Rotodoser).
By Construction and Sanitization
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Split body/cantilever: Facilitates rotor extraction without removing the valve from the line; speeds up cleaning/inspection.
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Sanitary design with internal rounded edges, concealed fasteners, and polished surfaces: Minimizes retention and facilitates CIP/SIP.
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Blow-through vs. drop-through execution (see above).
By Material and Finish
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AISI 316L (pharma standard) with electropolishing; typical roughness Ra ≤ 0.8 μm (many applications require Ra ≤ 0.5/0.4 μm).
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Hastelloy (C-22/C-276) for more corrosive environments.
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Rotors in 316L or engineering polymers (e.g., PEEK) to reduce friction/adhesion; seals in FDA/USP Class VI materials (PTFE, EPDM, FKM, silicone).
Selection Criteria — From Powder to Process
For correct specification, consider product properties and process conditions:
Particle Size & Shape
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Cohesive fines (e.g., micronized API) pack/adhere: favor polished surfaces, rounded rotor, possible anti-stick coatings, and hopper flow aids.
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Larger, free-flowing granules: Focus on volumetric capacity and airlock.
Hygroscopicity and Static Electricity
- Hygroscopic products tend to adhere; consider dry air purge and environmental control.
- Electrostatic charges require grounding and, sometimes, antistatic materials.
Abrasiveness
- Hard particles require robust materials (316L with treatments/hardness, or Hastelloy) and correct clearances to avoid premature wear.
Bulk Density and Required Flow Rate
- Size volume per revolution and RPM range; for dosing, verify flow stability (may require closed-loop control with upstream/downstream weighing).
Pressure/Temperature
- Assess if the valve will operate as airlock (ΔP). Ensure seals and clearances support operating temperature (and CIP/SIP, if present).
ATEX / Dust Hazard
- Identify area classification and require compliant execution (grounding, certified components).
Cleaning and Validation (cGMP)
- Need for quick disassembly and/or CIP/SIP; material traceability, certifications (FDA/USP), IQ/OQ, and documentation.
Mechanical Interfaces
- Sanitary connections (Tri-Clamp, SMS, BFM®/cuffs), orientation (vertical/horizontal), space for rotor extraction (if cantilever).
Sanitary and Compliance Requirements
In pharmaceuticals, the rotary valve must comply with cGMP and applicable regulations, including:
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Contact materials: AISI 316L as standard; gaskets/seals with FDA compliance (21 CFR) and, when required, USP Class VI; for greater corrosion, Hastelloy.
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Surface finish: Ra ≤ 0.8 μm (common) or better based on retention/cleaning risk. Electropolishing recommended.
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Sanitary design: Continuous surfaces, internal radii, absence of crevices/exposed threads in product zone, quick rotor/housing disassembly.
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Cleaning: CIP/SIP compatibility where applicable (adequate geometries and seals) or tool-less disassembly for validatable manual cleaning.
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Documentation: DQ/IQ/OQ, material certificates, traceability, cleaning/maintenance manuals, and spare parts list.
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Safety: ATEX compliance/zones with explosive dusts, grounding, and mechanical guards.
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Food contact: Where interfaces with nutraceuticals/foods exist, also attention to Reg. (EC) 1935/2004.
Line Integration — Connections and Typical Layouts
With Pneumatic Conveyors
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Blow-through: Rotor discharges directly into the pipeline, optimizing air pick-up; indicated when space is critical or there’s risk of outlet accumulation.
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Drop-through with downstream pick-up: Common in dilute phase; may require by-pass/vent to balance pressures and reduce re-aeration in hopper.
With Silos/IBC, Mills, Mixers, and Presses
- In IBC/silo discharge, the valve acts as feeder; combine with massagers, vibrators, or fluidizing cones for cohesive powders.
- In mill/mixer feeding: aim for stable flow and anti-segregation.
- Upstream of presses/encapsulation machines, if fine dosing is needed, evaluate Rotodoser-type solutions (micro-dosing) with speed control and, if necessary, closed loop via check scale.
Automation & Control
- Variable frequency drive (VFD) to regulate flow rate.
- Rotation/torque sensors for protection/diagnostics.
- Interlocks with upstream/downstream (pressure switches, level).
- Product recipes (RPM, setpoints, permissives).
Common Problems and How to Solve Them
Packing/Bridging in Hopper
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Causes: Cohesive powder, moisture, low energy in hopper.
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Solutions: Flow aids (vibrator, massager), adequate hopper angle, anti-stick coatings, dry air purge, rotor/blades with gentle geometry.
Abrasion and Wear
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Causes: Hard particles; unsuitable clearances.
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Solutions: Resistant materials/treatments (high-hardness 316L, Hastelloy), correct clearances, replaceable tips (e.g., PTFE) where applicable.
Airlock Loss / Air Leakage
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Causes: Rotor/seal wear; excessive clearance.
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Solutions: Preventive maintenance, flexible tips, ΔP verification, and hopper venting.
Product Degradation / Fines Generation
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Causes: Aggressive blades; high RPM.
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Solutions: Rounded rotor, lower RPM, greater volume per revolution (same flow rate at lower speed).
Carry-over / Retention
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Causes: Geometries with sharp edges; poor finish.
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Solutions: Polishing/electropolishing, rounded edges, sanitary design without dead zones.
Practical Cases (Illustrative Examples)
Case 1 — Stable Feeding of Tablet Press (API + Excipient)
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Challenge: Sensitive and partially cohesive blend generated tablet weight variability.
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Solution: Sanitary rotary valve with rounded rotor, Ra ≤ 0.5 μm, VFD control, and air by-pass to stabilize hopper pressure.
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Result: Reduced feeding variability, better tablet uniformity, and less re-work.
Case 2 — Blow-through Pneumatic Conveying on Hygroscopic Granule
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Challenge: Outlet accumulation in drop-through configuration and moisture absorption in hopper.
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Solution: Migration to blow-through, dry air purge in loading zone, USP Class VI seals compatible with SIP.
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Result: Elimination of accumulation, fewer cleaning stops, and preservation of flowability.
Comparative Table — Materials & Seals (Technical Summary)
| Contact Element |
Typical Options |
When to Prefer |
Pharma Notes |
| Body/covers |
AISI 316L |
Pharmaceutical standard |
Electropolished; Ra ≤ 0.8/0.5/0.4 μm according to risk |
| Body/covers |
Hastelloy C-22/C-276 |
Aggressive/corrosive environment |
Higher cost; evaluate only if necessary |
| Rotor |
Polished 316L |
Versatile and robust |
Less adhesion with high polish |
| Rotor |
PEEK (engineering polymer) |
Reduces friction/adhesion |
Verify thermal/SIP compatibility |
| Tips/seals |
PTFE (FDA/USP VI) |
Low friction and chemical inertness |
Possible spring version (lip seals) |
| Seal |
EPDM (FDA/USP VI) |
Water/alkaline CIP |
Verify compatibility with solvents/flavors |
| Seal |
FKM/Viton® (FDA/USP VI) |
Solvents/oils |
Temperature limit according to grade |
| Seal |
Silicone (FDA/USP VI) |
Wide compatibility |
Good temperature range; attention to solvents |
Note: Final choice depends on product, cleaning, temperature, ΔP, CIP/SIP, and validation requirements.
Technical Checklist for RFQ (for Gated PDF)
Use this checklist to request a targeted technical quote:
On the Product (powder/granule)
- Name/composition (indicate API/excipients that impact compatibility)
- Particle size (D10/D50/D90) and bulk density
- Cohesion/hygroscopicity (e.g., angle of repose, compressibility index)
- Abrasiveness and sensitivity to degradation
- Operating temperature/humidity
On the Process
- Valve function: airlock, feeder, or doser (micro-dosing?)
- Minimum/maximum flow rate (kg/h) and required stability
- Position (drop-through/blow-through), available space, orientation
- ΔP between upstream/downstream and operating pressure/temperature
- Integrations: silo/IBC, mixer, mill, press, pneumatic conveying (phase, air flow rate)
Mechanical & Sanitary Execution
- Body/rotor material (316L, Hastelloy, PEEK rotor?)
- Required internal finish (Ra target) and electropolishing
- Gaskets/seals (PTFE, EPDM, FKM, silicone; require FDA/USP VI)
- Quick disassembly/cantilever; CIP/SIP (yes/no)
- Connections (Tri-Clamp, SMS, BFM®/cuff), internal radius requirements, and absence of crevices
Automation & Control
- RPM range; motor + inverter; sensors (speed/torque)
- Safety interlocks and permissives
- Dosing repeatability/control level (if in loop)
Documentation & Validation
- Material and seal certificates (FDA, USP VI)
- DQ/IQ/OQ, FAT/SAT, cleaning/maintenance manuals
- Critical spare parts list (seals, tips, rotor)
Technical FAQ
1) Can the rotary valve dose with precision?
Yes, in volumetric dosing where flow rate is a function of volume/revolution and RPM. For greater precision/repeatability, closed-loop (weighing) or dedicated micro-dosing solutions (e.g., Rotodoser) are recommended.
2) How to choose between drop-through and blow-through?
Blow-through is preferable when downstream pneumatic conveying exists and there’s risk of outlet accumulation/moisture; drop-through is simple and robust for gravity feeding.
3) Is CIP/SIP possible?
It depends on design. Sanitary executions compatible with CIP/SIP exist; others adopt validatable quick disassembly. Define in RFQ.
4) What determines the finish (Ra)?
The retention risk and cleaning method. Cohesive products and manual cleaning require lower Ra (≤ 0.5/0.4 μm). Electropolishing helps.
5) How to avoid particle degradation?
Use rounded rotor, lower RPM, and greater volume per revolution for the same flow rate; minimize aggressive clearances.
6) Which seals to choose?
Depends on chemistry/temperature/CIP. PTFE is inert and low-friction; EPDM/FKM/silicone vary according to solvents and temperature. Require FDA/USP VI.
7) Is the valve ATEX compliant?
Yes, when specified and built for the zone. Include classification in RFQ and ensure grounding and suitable components.
8) When to consider Hastelloy?
Only in the presence of significant corrosion that makes 316L critical — evaluate cost/benefit.
Good Installation & Maintenance Practices
- Provide frontal space for rotor extraction (if cantilever) and inspection access.
- Install by-pass/vent to stabilize hopper pressure.
- Ground all sections to avoid charges.
- Maintenance plan with periodic verification of clearances, seals, and rotor wear.
- Validated cleaning procedures, with steps and post-reassembly controls.
- Minimum spare parts kit: seal set, tips (if applicable), and rotor (when critical for uptime).
