In industrial production lines where bulk materials such as powders, granules, pellets, and similar substances are used, the orderly transfer of the product from one piece of equipment to another is critical to process continuity. Problems such as uncontrolled product discharge, air leaks, reduced line capacity, impaired filter performance, or equipment overload are often caused by the incorrect selection of feeding equipment.
In this context, the rotary valve is one of the most widely used systems for controlling material transfer between different process equipment. In Turkish, it may be referred to as a rotary valve, rotary gate, star valve, star feeder, cell wheel, or—particularly in applications where air control is critical—an air lock.
The scope of rotary valve systems is not limited to silo-bottom discharge. They can be used in a wide variety of applications, ranging from pneumatic conveying systems under filters and cyclones to big bag discharge, mixers, and dosing lines.
In this article, we will discuss in detail where rotary valves are used, what roles they play in different applications, and what technical criteria should be considered when selecting a rotary valve based on the application.
What Is a Rotary Valve Used For?
A rotary valve is a mechanical process equipment that transports bulk materials in specific volumes using a rotor with blades that rotate inside the housing.
The product fills the rotor chambers through the top inlet. As the rotor rotates, the material is transported to the bottom outlet. Thanks to this operating principle, a more controlled flow is created instead of uncontrolled discharge of the product.
Rotary valves are primarily used for the following purposes:
- Controlling product flow
- Controlled discharge from silos and bunkers
- Discharging dust collected in filters
- Discharging product from cyclones
- Feeding product into pneumatic conveying lines
- Restricting air flow between two different pressure zones
- Feeding product from big bag systems
- Transferring product to mixers and dosing lines
The actual function of the equipment varies depending on the process point to which it is connected. Therefore, when selecting a rotary valve, not only the product name but also the point of use must be taken into account.
Use of Rotary Valves Under Silos
The area under silos is one of the most common applications for rotary valve systems.
It is not always desirable for powder or granular product stored in a silo to discharge freely into downstream equipment. Due to the pressure created by the tall product column, the product may flow too quickly or cause excessive load on the connected equipment.
Rotary valves at the bottom of silos transfer material from the silo in a controlled manner using rotor cells.
In this application, rotary valves can provide the following advantages:
- Regulates product flow
- Reduces overfeeding of downstream equipment
- Provides continuous and controlled feeding
- Creates a transition between the silo and the conveying line
- Supports dosing or conveying systems
When selecting a rotary valve for use at the base of a silo, the height of the product column must also be evaluated. Very high product pressure can affect the filling behavior of the rotor cells.
Factors to Consider When Selecting a Rotary Valve for Use Below a Silo
- Product density
- Silo outlet size
- Capacity requirements
- Particle size
- Product flowability
- Product height inside the silo
- Tendency to bridge
- Rotor speed
- Type of downstream equipment
A rotary valve used below a silo typically works in conjunction with a screw conveyor, belt conveyor, pneumatic conveying system, or mixer.
Use of Rotary Valves Under Bunkers
Bunkers serve as intermediate storage points on the production line. The rotary valve used under a bunker is designed to feed the product steadily to the next process equipment.
For example, on a production line, the product may move in the following sequence:
Big bag unloading → bunker → rotary valve → pneumatic conveying → silo
In this case, the rotary valve ensures that the product inside the bunker is transferred to the pneumatic line in a controlled manner.
In applications under bunkers, changes in product level must be considered in addition to capacity. The product load on the rotor may differ when the bunker is completely full compared to when the product level is low.
Use of Rotary Valves Under Cyclones
Cyclones are process equipment that separates products within an air stream using centrifugal force. The separated product accumulates in the lower conical section of the cyclone.
This product must be discharged in a controlled manner.
The rotary valve under the cyclone facilitates product discharge while also limiting airflow between the cyclone and the external environment.
For this reason, the equipment is often referred to as an airlock or rotary airlock in this application.
Why is a rotary valve under a cyclone important?
If the area under the cyclone is left completely open, outside air may enter. This airflow can:
- affect the cyclone’s separation performance,
- alter the system’s air balance,
- increase the fan load,
- and cause product backflow.
Using a rotary valve reduces direct air flow during product discharge.
Selection Criteria for the Cyclone Outlet
- Air flow rate
- System pressure or vacuum
- Product density
- Particle size
- Hourly product volume
- Temperature
- Abrasiveness
- Air leakage tolerance
The clearance between the rotor and the housing is particularly important in systems that handle fine dust.
Use of Rotary Valves Below Filters
In jet pulse and similar industrial filters, dust separated from the air accumulates in the filter’s lower hopper.
This dust must be discharged continuously or at specific intervals.
The rotary valve under the filter removes the accumulated dust from the system in a controlled manner.
In this application, the rotary valve can perform two important functions:
- Discharging the collected dust
- Reducing uncontrolled air ingress into the filter
If the filter system is operating under negative pressure, an open discharge point can draw in a significant amount of air from the outside. This can affect filter performance and fan capacity.
Using a rotary airlock helps reduce this air ingress.
An internal link to the Cyclonic Jet Pulse Filter product page should be provided in this section.
How Does the Rotary Valve Under the Jet Pulse Filter Work?
In a jet pulse filter, dust is trapped on the surface of the filter elements. Dust particles, cleaned by pressurized air pulses, fall into the lower hopper.
The product accumulated in the lower hopper reaches the rotary valve inlet.
As the rotor turns:
- the product fills the cells,
- is transported to the outlet,
- is transferred to downstream equipment,
- and the open passage between the filter and the external environment is restricted.
This design ensures regular product discharge, particularly in continuously operating filter systems.
The rotary valve selected for use below the filter must be appropriately designed to prevent fine dust from entering the bearing and sealing areas.
Use of Rotary Valves in Pneumatic Conveying Systems
Pneumatic conveying is one of the most technical applications of rotary valves.
In pneumatic conveying systems, material is transported through the pipeline by an air flow. A rotary valve can feed the product from a silo or bunker at atmospheric pressure into the conveying line in a controlled manner.
At this point, simply transferring the product is not sufficient. Air loss in the conveying line must also be minimized.
For this reason, the rotary valve used in pneumatic conveying lines is often classified as a rotary airlock valve.
Why does a rotary valve act as an airlock?
The rotor blades prevent a continuously open channel from forming between the inlet and outlet.
Thus:
- air leakage from the pressurized line is reduced,
- uncontrolled air ingress from outside into the vacuum line is limited,
- product feeding is more consistent,
- and the air balance of the conveying system is maintained.
An internal link to the Pneumatic Conveying Systems page should be provided from this section.
Rotary Valves in Positive-Pressure Pneumatic Conveying
In positive-pressure systems, the air generated by the blower provides the conveying force in the pipeline.
The rotary valve feeds the product from the silo or bunker into the pressurized line.
The most significant problem here is the escape of conveying air upward through the rotary valve.
When air leakage is excessive:
- system capacity may decrease,
- blower energy consumption may increase,
- the product may not fill the rotor chambers properly,
- and air may be blown back into the silo.
Therefore, operating pressure and air leakage are critical parameters in selecting a rotary valve for pressurized lines.
Rotary Valve in Vacuum Conveying Systems
In vacuum systems, the conveying line operates under negative pressure.
Rotary valves are typically used in these systems to discharge the product from the receiving hopper.
If open discharge is used, excessive outside air may enter the system.
This situation:
- lowers the vacuum level,
- affects conveying capacity,
- increases filter load,
- and may raise energy consumption.
The rotary valve helps limit the inflow of outside air while discharging the product.
It is recommended to include a link to the Vacuum Conveyor product page in this section.
Rotary Valve in Big Bag Discharge Systems
In big bag systems, the product inside the bag must be transferred to the next process after discharge.
Connecting the big bag outlet directly to a pneumatic line or a dosing system may not always be suitable.
In this case, a rotary valve can be used.
Example process:
Big Bag → Discharge Hopper → Rotary Valve → Pneumatic Conveying → Silo
In this configuration, the rotary valve:
- regulates the product flow from the big bag,
- provides controlled feeding to the pneumatic system,
- reduces sudden product loading,
- and helps limit air ingress.
In Big Bag systems, the product’s flow properties are critical. For materials prone to bridging or caking, a rotary valve alone may not be sufficient; vibration or flow-aiding systems may be required.
An internal link to the Big Bag Discharge product page should be provided from this section.
Rotary Valves in Mixer and Blender Lines
In mixers, rotary valves can be used at both the inlet and outlet points.
At the mixer inlet
It ensures controlled feeding of the product into the mixer.
This is particularly important in recipe-based production. Excessive or irregular feeding can affect mixing ratios.
At the mixer outlet
It facilitates the transfer of the mixed product to the next process equipment.
Especially if a large amount of product accumulates under the mixer, discharging the entire batch at once can place an excessive load on the downstream equipment.
A rotary valve can provide controlled product flow.
An internal link to the Mixer product page should be provided from this section.
Rotary Valves in Dosing Systems
Since rotary valves operate on the principle of volumetric feeding, they can be used for dosing in some applications.
The approximate product feed rate can be adjusted by controlling the rotor chamber volume and rotor speed.
However, a rotary valve is not always a high-precision dosing device.
The actual feed rate is influenced by the following factors:
- product density,
- rotor chamber fill ratio,
- product flowability,
- rotor speed,
- bunker level,
- product buildup.
If high dosing accuracy is required, a load cell, gravimetric feeder, or other dosing systems may be necessary.
Use of a Rotary Valve Before a Screw Conveyor
A rotary valve can be used upstream of screw conveyor feeding systems to regulate product flow.
In particular, if product from the silo outlet is fed directly into the screw conveyor, the screw conveyor may become overloaded.
By using a rotary valve:
- the feed rate is controlled,
- the auger load is reduced,
- motor strain is prevented,
- and the system can operate more stably.
An internal link to the Auger product page should be provided from this section.
In Which Industries Are Rotary Valves Used?
Rotary valve systems can be used with various products across many industries.
Food industry
- Flour
- Sugar
- Starch
- Cocoa
- Spices
- Milk powder
- Feed additives
Hygienic design, stainless steel, and easy-to-clean rotor options may be important.
Chemical industry
- Pigments
- Powdered chemicals
- Additives
- Filler materials
Chemical compatibility and leak-tightness should be evaluated.
Plastics Industry
- Plastic pellets
- Masterbatch
- Powdered additives
Factors such as product breakage and static electricity may be taken into account.
Cement and Minerals Industry
- Cement
- Ash
- Mineral powders
- Lime
Abrasion resistance is a key design criterion for these products.
Feed Industry
- Grain products
- Premixes
- Feed additives
High capacity and consistent feeding are key priorities.
Rotary Valve Selection Based on Application
The same rotary valve should not be used for all applications.
Application Point Primary Selection Criteria
Under a silo Product load and capacity
Under a bunker Consistent feeding
Under a cyclone Air leakage
Under a filter Fine dust and leak-tightness
Pneumatic Conveying: Pressure Differential
Vacuum System: Limiting Outside Air Inlet
Big Bag: Flow Control
Mixer: Batch Operation and Product Discharge
Food Processing: Hygiene and Cleanliness
Mineral Processing: Wear Resistance
Therefore, when requesting a technical quote, the intended application of the rotary valve must be clearly specified.
Technical Information Required for Rotary Valve Selection
The following information must be provided for a proper system evaluation:
Information Description
Product Material to be conveyed
Bulk density kg/m³
Capacity kg/h or t/h
Particle size Minimum and maximum
Temperature Product and ambient
Pressure Positive or negative
Point of use Silo, filter, cyclone, etc.
Abrasiveness: Low, medium, high
Moisture: May affect product flow
Hygiene: Stainless steel requirement
Operating Mode: Continuous or intermittent
Explosive Atmosphere: ATEX assessment
Selecting a rotary valve based solely on the connection diameter without this information is incorrect.
Common Mistakes in Rotary Valve Use
Using the same rotary valve for every application
The design requirements for an airlock operating under a filter may not be the same as those for a feeder under a silo.
Failing to specify the pressure value
In pneumatic conveying systems, sealing performance cannot be properly evaluated without pressure information.
Failing to consider product density
Even if the rotor volume appears correct, the actual capacity in metric tons per hour may be insufficient.
Ignoring Wear
With abrasive products, the tolerance between the rotor and the housing increases over time, leading to increased air leakage.
Focusing Only on Motor Power
Rotary valve performance is more closely related to rotor volume, rotational speed, product characteristics, and tolerances than to motor power.
Frequently Asked Questions
Where are rotary valves most commonly used?
Silos, bunkers, filters, cyclones, and pneumatic conveying lines are among the most common applications.
Why is a rotary valve used downstream of a filter?
It helps reduce uncontrolled air ingress into the system when discharging dust collected in the filter.
Is a rotary valve necessary downstream of a cyclone?
If the cyclone operates under pressure or vacuum, using a rotary airlock may be important to maintain air balance.
Can a rotary valve feed material into a pneumatic conveying system?
Yes. A rotary valve with adequate pressure resistance and proper rotor-to-housing tolerances can be used to feed material into a pneumatic conveying line.
What is the purpose of a rotary valve in a big bag discharge system?
It ensures that the material discharged from the big bag is fed into the next process in a controlled manner.
Can a rotary valve be used for dosing?
Volumetric feeding is possible, but additional dosing systems may be required for applications that demand high precision.
Conclusion
Rotary valves are essential equipment used in a wide range of industrial processes, from silo and bunker discharge to filter and cyclone systems, and from pneumatic conveying lines to big bag, mixer, and dosing applications.
The function of a rotary valve may vary at each point of use. While controlled product feeding is a priority under silos, limiting air flow may be more critical under filters and cyclones. In pneumatic conveying systems, both product feeding and the reduction of pressure or vacuum loss are required.
For this reason, the selection of a rotary valve should not be based solely on product diameter or capacity. The point of use, product characteristics, pressure, temperature, wear, and hygiene conditions must all be evaluated together.
A properly engineered rotary valve regulates product flow, maintains system balance, and contributes to more reliable operation of the production line.
Let’s Determine the Rotary Valve Solution Right for Your Application
Share the application point, the product to be conveyed, bulk density, hourly capacity, temperature, and operating pressure with the MASTRON engineering team. Let’s evaluate the rotor, housing, drive, and connection options best suited for your application together.