Rotary airlock valves play important roles within industries involved in bulk material handling. Equipment used for material processing relies upon rotary airlock valves to feed product into material handling systems, regulate the pressure between different processes within the system, and load and unload raw or finished product. Positioned strategically between bulk material handling equipment within systems, rotary airlock valves help prevent air or gas leaks to maintain pressure differentials between processes. These important elements within processing systems also allow bulk solids in granular or powder form to pass through them while acting as feeding devices. Rotary airlock valves are critical to producing many products, helping ensure consistency, prevent product loss, and minimize wear on bulk material handling equipment.
A Key Element of Bulk Material Handling Equipment & Systems
Rotary airlock valves are often called by different names, depending on their exact application within a system. Generally referred to as rotary valves, they’re also known as airlocks, blowing seals, feeder valves, rotary airlocks, or rotary airlock feeders. They can isolate systems from areas with environments of differing pressures and are typically used in pneumatic conveying systems for bulk material handling. Equipment connected to these rotary valves depends on them to maintain the efficiency of the entire processing system.
Bulk material handling equipment and systems use rotary airlock valves to:
- Unload fine particles from dust collection systems while the system continues to operate.
- Regulate feed rates of raw material entering a processing system.
- Reduce worker injuries by helping prevent pressure surges in pneumatic conveying systems that can lead to dust explosions.
- Provide a barrier against conflagrations or explosions.
- Keep pressure levels within acceptable parameters to inhibit air leakage and lower noise levels.
- Feed doses of material into pneumatic conveying systems.
- Create a seal between two processes to prevent dust or other contaminants from entering.
- Control the flow of materials by acting as an airlock between pressurized processes so that the product flows only in one direction.
- Control processing volume and metering of product.
Rotary airlock valves integrated into industrial bulk material handling equipment serve three primary purposes: metering, loading/unloading of bulk materials, and pressure regulation.
Metering Applications for Bulk Material Handling Equipment
In bulk material handling, equipment adds value to product during processing. Rotary airlock valves, for example, are used in the milling of granulated sugar to produce finer confectionary or other powdered sugars for baking. Pharmaceutical companies use these devices within their systems to mix together active and inactive ingredients for medications. In the mineral processing sector, lime powders are classified and screened with the help of rotary airlock valves.
In fact, bulk material handling equipment of all types relies on rotary valves to control product feed so that they function appropriately. Air classifier, cone, jet and pin mills all need material to flow at a controlled rate to grind material effectively and add to the value of a bulk material. Handling equipment relies on rotary valves to regulate the feeding of material from storage areas upstream and into vessels where ingredients are transported and mixed. With a device like a rotary valve, these mills would overflow with product and become inefficient, or even stop working altogether.
Rotary valves used for metering activities are simply constructed and compact. They’re especially useful in phased processes, where product is fed from bulk bags or hoppers via gravity into milling, screening, or other bulk material handling equipment. Though there are numerous means for metering product passing through systems used for bulk material handling, equipment like rotary valves provide an effective yet simple solution.
Loading & Unloading of Bulk Material Handling Equipment
Dust collection systems are critical to many bulk material handling systems. Equipment connected to rotary airlock valves maintains a constant vacuum or pressure that conveys finer particles from upstream processes, so that dust collecting devices function properly. Acting as an airlock, these devices help maintain the efficiency of systems designed for bulk material handling. Equipment filters that become blocked with dust or overloaded with product receive intermittent pulses of high-pressure air to clear them of material. The heavier material collects at the bottom of the filter housing.
Clearing this dust away after it falls from the filtering devices within bulk material handling equipment can be done in one of two ways. One method involves shutting down the whole dust collection system, opening the hopper, and unloading these fine materials into a dust bag, drum, sack, or other collection device. Alternatively, a rotary airlock valve can maintain a vacuum seal, so the fine materials can be discharged without shutting down the dust collection system. In this case, rotary airlock valves minimize downtime while increasing safety by decreasing the need for operators to intervene. Additionally, by maintaining a vacuum with a rotary valve airlock, manufacturers can reclaim and recycle more product, which curtails waste.
Pressure Regulation in Bulk Material Handling Equipment
Feeding pneumatic conveying systems requires a rotary airlock valve to safely introduce material into a system or between processes during bulk material handling. Equipment for conveying using pneumatics is often connected to rotary airlock valves. Dilute phase positive pressure conveying involves pressurized air conveying materials that are lighter and less abrasive at high velocities within an airstream, Vacuum conveying systems instead use negative pressure to draw materials down piping systems from feeding points.
Though rotary valve airlocks aren’t airtight, they create a barrier that maintains a sufficient pressure differential to sustain pneumatic conveying during bulk material handling. Equipment tolerances for rotary airlocks used in this way must be extraordinarily tight, in many cases with a valve housing within .004 to .006 inch (101.6 to 152.4 microns) of the rotating vanes. Generally, a rotary airlock valve will be placed within a system beneath big bag unloading stations, hoppers, intermediate bulk containers, and silos.
At these points, gravity causes materials to discharge into a rotary airlock’s pocketed vanes. As the valve turns, it creates a seal against the pressure differential, enabling material to fall into the pneumatic stream. With this design, the material then “blows through” the rotary airlock valve as the air conveying it carries it through the drop stream beneath the valve. As the pressure of pneumatic conveying systems causes material to seek the path that offers least resistance, once material is discharged the pressure within the system replaces it.
As each pocket turns back towards the inlet, pressure escapes into the storage container from which material feeds the airlock. This pressure builds over time, leading to equipment issues, including potential failure. There are two possible solutions to prevent this. A degassing vent can be added to the return side of the rotary airlock’s housing, which can then connect to a centralized dust system. Another method involves installing a reverse air jet filter to the storage vessel, feeding the airlock. Both these techniques prevent pressure from building as the valve turns.
Correctly Sizing Rotary Airlock Valves
Sizing a rotary airlock correctly involves careful consideration of various factors.
These factors include:
- Flowrate conditions: A rotary valve’s capacity needs to match the throughput it must handle, which is normally measured either in cubic feet per minute (CFM) or pounds per hour; alternatively, in metric terms, these are measured as cubic meters per minute or kilograms per hour.
- Material properties: The abrasiveness, density, flowability and particle size of materials help determine the type of rotary valve needed, with abrasive and heavier materials requiring more heavy-duty models.
- Pressure differentials: Rotary valves must be able to withstand the difference in pressures between different processes within a system.
- Temperature: Construction materials and designs for rotary valves must be able to handle operating temperatures without deforming or wearing out prematurely.
- Valve speed: To control the flowrate and prevent the rotary valve from clogging, it’s important to regulate the speed at which a valve’s vanes spin, particularly when conveying stickier or finer materials.
Properly sizing a rotary valve will minimize air leakage and wear, while ensuring safety and efficiency. Certain bulk material handling equipment manufacturers offer tools to estimate and recommend the best size of rotary airlock valve for their application.
Prater Rotary Airlock Valves for Bulk Material Handling
Prater Industries manufactures several models of rotary airlock valves for use with other bulk material handling equipment. Our rotary valves work for metering dry materials while minimizing pressure loss as airlocks throughout material processing systems and loading and unloading products and ingredients. Prater’s rotary valves can be customized and configured for almost any application, including specially designed abrasion-resistant models. Our rotary valves are ideal as feeding devices, as they’re fabricated with larger pockets and made to last longer and minimize air leakage.
Prater’s various rotary airlock valves are designed to:
- Control material flow from one process to another
- Feed materials into pneumatic conveying lines
- Maintain a pressure differential between containers or processes, while also minimizing air loss
- Meter ingredients or finished product for unloading and loading purposes
To learn more about our rotary airlock valves, other bulk material handling equipment, and our relevant services, contact the experts at Prater today.
