Rotary Airlock Valves & Their Fabrication

Referred to commonly as a rotary airlock or rotary feeder, depending on how it’s used, it’s important to understand what this device does before looking at the intricacies of designing and manufacturing a rotary airlock valve. Manufacturers of these valves, used for feeding bulk solids within a processing system, understand that rotation is key to how this mechanism works. As essential components for many bulk handling operations, the vanes on the valve rotate to provide a consistent and continuous feed into a processing system.

A rotary airlock valve’s two primary functions are to: 

  • Regulate flow rates of material in a processing system.
  • Maintain consistent air pressure within the system by preventing air from leaking.

Material enters the valve through an inlet while exiting through an outlet, with the speed of the mechanism’s vanes controlling flow rates. As it operates, material entering the valve is scooped up within the vanes’ pockets as they spin around the rotor’s shaft. Though simple in construction, there are various ways to modify a rotary airlock valve. Manufacturers use scientific principles to adjust valve designs to handle certain applications better.

When used incorrectly, however, rotary airlock valves can create inefficiencies in production processes, degrading products and accelerating equipment wear, leading to unplanned downtime. The best rotary airlock valve manufacturers design these machines to improve operational performance and efficiency during production. This involves a meticulous design to ensure accurate measurement of materials as they’re loaded and unloaded from the vanes’ pockets while minimizing pressure loss during processing.

Design Considerations for Rotary Airlock Valve Manufacturers

For material handling systems, various factors affect the design of a rotary airlock valve. Manufacturers must consider pressures and temperatures the device must withstand, for example, which will affect its construction and the materials from which it’s made. Rotary airlock valve specifications will, as a result, differ according to the application for which it’s used. Because of its importance for conveying and processing systems, specific design elements may be considered for an application involving a rotary airlock valve. Manufacturers must consider the environment in which the device will operate, designing and building valve components that best suit these conditions.

Valve designs used for high pressures and temperatures might consider: 

  • Rotor: Featuring closed vanes as these better withstand high pressures than open ones.
  • Flange: It should resist high pressures and temperatures well for efficient processing.
  • Packing seal: Referring to the gap between the bearing housing and rotor shaft, it should leak air only minimally.
  • Rotor shaft: Tolerates high pressures and temperatures while minimizing shaft deflection.
  • Vane tips: Making these easily accessible allows operators to fine-tune clearances between the vane tips and housing while allowing tips to be replaced instead of the whole vane set to lower maintenance costs.
  • Vanes: Must withstand high pressures and temperatures.

Specifications differ depending on the main function of the rotary airlock valve. Manufacturers customize these devices to meet the conditions expected in certain applications. For this reason, rotary airlock valve manufacturers use different configurations and construction materials for these devices. For example, one valve design may concentrate on minimizing air loss between equipment in a processing system, or another may wish to control the feed rate of the product better. Using rotary airlock valves for dust control might be a higher priority for other applications.

A central aspect of rotary airlock valve design involves the valve assembly, where the vanes attached to the rotor’s shaft revolve within the housing. As product enters and the vanes rotate, the pockets between them fill uniformly with material, ensuring a consistent feed from the device’s outlet. The requirements for handling material also determine the dimensions and number of vanes needed within a rotary airlock valve. Manufacturers understand that the more vanes a valve has, the better it seals, while larger pockets work better for bulkier, compacted, or more viscous materials. However, Denser materials and those that flow easily aren’t affected by pocket size or number of vanes.

Additionally, construction material can alter the characteristics of a rotary airlock valve. Depending on the application, manufacturers often use cast iron or stainless steel for the body, drive, and internal rotor. Certain valves will be treated with chrome, ceramic, or other coatings that better serve certain applications. The cost of construction materials will also factor into this as well.

Construction Material for Rotary Airlock Valve Manufacturers

Crucial to pneumatic systems, rotary airlock valve manufacturers need to consider the applications for which they will be used. Determining the application will define the types of materials that are appropriate for a rotatory airlock valve. Manufacturers must also consider the construction material for how well it handles the specific production environment, as certain materials resist wear better, depending on the conditions in which a valve is used.  

Construction materials rotary airlock valve manufacturers commonly use include: 

  • Aluminum: When weight is a meaningful factor, lighter-weight aluminum parts are sometimes used in the device’s production.
  • Carbon steel: Often used for a rotary airlock valve’s endplates, rotor, and other components, carbon steel provides the valve with durability and strength to withstand various operational conditions. 
  • Cast iron: With good wear resistance and strength, cast iron endplates and housings are common features in a rotary airlock valve; manufacturers sometimes use cast iron variants like ductile or gray iron for certain applications or parts.
  • Ceramic coated: Manufacturers will often coat rotary airlock valves with a ceramic coating to prevent wear for applications that require working with abrasive materials.
  • Composite materials: When chemical resistance is a consideration, composite materials containing plastic polymers with other constituent materials are used for coatings or housings to extend lifespan and moderate wear.
  • Specialty coatings: Rotary airlock valve manufacturers use specialty coatings like tungsten carbide for certain challenging environments to augment durability and extend their lifespan.
  • Stainless steel: Typically, the more corrosion-resistant stainless steels like 304 or 316 are used to construct a rotary airlock valve; manufacturers will generally use stainless steel for valves meant to operate in particularly harsh conditions.
  • Tool steel: Sometimes referred to as hardened steel, tool steel is used for rotors, especially when working with abrasive materials, as it extends its lifespan considerably.

While materials are especially important in applications involving harsh conditions, such as working with abrasive or corrosive materials, craftmanship is also incredibly important when producing a rotary airlock valve. Manufacturers must use proven methods to construct valves and other processing machinery.

Fabrication Techniques for Rotary Airlock Valve Manufacturers

Manufacturers must consider many different aspects of production during the fabrication of a rotary airlock valve. For example, when casting a housing for a valve, one of the most important qualities to consider is that it has no crevices or pits. Like any precision machine, a valve made via casting must present smooth surfaces to prevent contaminants or products from sticking to the sides. Smooth surfaces also enhance operational efficiency, ensuring that they seal appropriately.

In this same vein, tight tolerances are necessary to ensure compliance with NFPA (National Fire Protection Association) standards. This also guarantees that material flows efficiently while ensuring it doesn’t get stuck in the valve or blow back through the inlet. Efficiency extends to energy as well. Manufacturers often fit a direct drive motor to augment energy efficiency when designing a rotary airlock valve. Conventional drives create excessive resistance, while direct drives use less energy by producing higher torque with fewer rotations per minute.

While casings are normally cast when fabricating a rotary airlock valve, manufacturers often use CNC (computer numerical control) machining for valve components. CNC machining ensures precision and accuracy for parts that are difficult to attain through other manufacturing methods. The tight tolerances achieved with CNC technology also help prevent leaks from fine particles that go beyond the rotary shaft’s seals, which is especially important for pressurized conveying systems. For this reason, many valve manufacturers include purge systems or alternative seal options to extend valve lifespans. 

Prater Industries: Rotary Airlock Valve Manufacturers

Prater Industries has been manufacturing material handling equipment for nearly a century, including many types of rotary airlock valves. Manufacturers using Prater machinery come from dozens of industries, using our equipment for countless applications. As one of the premier makers of rotary airlock valves globally, we take great pride in the design and craftsmanship that goes into each of our models of rotary airlock valves. Manufacturers of an array of high-quality valves, Prater engineers use their creativity and knowledge of material science to make some of the finest rotary airlock valves available for any industry. This includes customizing some of our rotary airlock valves for our customers to best suit specific applications.

Prater Rotary Airlock Valve Charcoal Industry Case Study

Let’s take a quick look at how Prater Industries deals with one of our valued customer’s issues regarding a production system that featured a Prater rotary airlock valve. A large manufacturer of charcoal, this customer had been using our valves at facilities throughout the country for well over a decade. Prater engineers were thus familiar with the customer’s processes. They had even developed a “standard” rotary airlock valve, manufacturing it with certain specifications that included rotor thickness, hardened coatings, and abrasion-resistant wear bars.

In any industry, practices and processes change as new regulations or scientific data present themselves. This was also the case with this charcoal manufacturer, which saw the interior lining of Prater’s valve experiencing undue wear from handling their abrasive product. As charcoal eroded the valve’s coating, moisture would leak into the device, causing corrosion that ate away at internal components. This caused the normally robust wear bars to weaken and eventually fail under too much pressure.

In response to troubles with the rotary airlock valve, the manufacturers approached Prater’s engineering team to help ascertain why this was happening. Using both creativity and knowledge from years of experience, the valve was redesigned to include a new type of coating that would better withstand corrosion and wear. This hardened coating enhanced durability to more effectively endure the conditions it used. Not only did this material offer this manufacturer superior wear resistance, it also allowed Prater to offer a superior product to other manufacturers working with abrasive materials in the future.

Prater Rotary Airlock Valves

Prater makes six different models of rotary airlock valves, with variations on each. As manufacturers of other top-quality material handling machinery, we can tailor our equipment to meet our customers’ needs.

Prater’s standard rotary airlock valves include: 

  • Abrasion-Resistant rotary airlock valves: Coming with a cast iron housing with a thick layer of alumina ceramic coating that extends its lifecycle, this valve handles highly corrosive and abrasive products while maintaining the machine’s tight tolerances.
  • Blow-Thru rotary airlock valves: Used for feeding pneumatic conveying equipment, manufacturers of this rotary airlock valve can readily clear vane pockets; featuring larger vane pockets, this valve’s compact design is made with precision CNC machining and casting.
  • Dust Collector Series rotary airlock valves: With features generally only found on a heavy-duty rotary airlock valve, manufacturers get a durable cast iron housing, along with eight-vaned, precision machined rotors with two extra tips that create a better seal against air leakage.
  • Heavy-Duty PAV Series rotary airlock valves: Used to feed free-flowing powders on pneumatic conveying lines, these valves are made from cast iron or stainless steel, with optional construction materials or coatings available for corrosive or abrasive products. And a variety of shaft seal upgrades. 
  • Quick Take Apart Series rotary airlock valves (with rails): With this QTA series rotary airlock valve, manufacturers get precision CNC machined components and a direct drive for energy efficiency, along with easy access without tools to internal components via a convenient rail design.
  • Quick Take Apart Series rotary airlock valves: Made from cast iron or stainless steel, this valve offers the same precision-machined and accessible internal components as others in Prater’s QTA series, without the rail.  

While keen to comment on our equipment's excellent craftsmanship and design, our engineers also like to point out the beauty in Prater’s various iterations of the rotary airlock valve. Manufacturers like Prater may not be artists, but we know how to combine aesthetics with workable solutions. To learn more about the art and science behind our rotary airlock valves and other material handling equipment, contact us today.