Also known as rotary airlocks, rotary valves, or simply valves, rotary airlock valves are crucial in many bulk material handling systems. They function as devices to feed products or manage pressure differences between processes, with their exact use varying based on the product or application. Valves can simultaneously serve as rotary feeders, rotary airlocks, or even both. Regardless of their role, regular maintenance is essential to function properly in bulk material processing.
Types of & Applications for Rotary Airlock Valves
There are numerous ways to configure a rotary airlock valve, and these configurations depend largely on the product's traits and the process type. Whether used as a rotary valve or airlock, these devices have a housing with an inlet and outlet port, a rotor shaft equipped with blades, two inboard or outboard end plates, and a drive system.
Rotors can be close-ended or open-ended, while blades can be adjustable or fixed. Each blade also has at least six pockets, though the exact number depends on the application. Housings come with various-shaped inlets, which can be circular, rectangular, or square, while construction materials might include cast iron, stainless steel, or other materials. Many rotary airlock valve manufacturers also offer optional coatings for working with abrasive products or for food processing applications.
The three general categories of rotary airlock valves are:
- Blow-through rotary airlock valves: Used with pneumatic, positive pressure convey systems, blow through models have ports in each end plate that connect directly to the convey circuit. Material dropping into the airlock inlet is rotated to the bottom of the housing, where the pneumatic air sweeps product directly thru each rotor pocket. Blow through valves are typically used for sticky products, or those with poor flow characteristics, such as flour, sugar, milk powders, and bakery mixes.
- Flow-through rotary airlock valves: Known as drop-through rotary valves, these valves have a body with vertically aligned inlet and outlet ports of the same size. Bulk solids fill empty rotor pockets at the top (inlet) and “drop” out of the pocket at the bottom (outlet). In some cases the outlet is connected to gravity spouting, other vessels, specialty process equipment, and even pneumatic convey lines via a specially designed adpator.These types of valves are used for applications with drier bulk materials that flow freely, such as coffee beans, rice, sand and wheat.
- Off-set rotary airlock valve: Also called side-entry valves, these devices feature an inlet and outlet that are not in line with the housing’s vertical line. As the rotor shaft rotates past the inlet, it only partially fills each empty rotor pocket. This, in turn, minimizes any shearing and jamming of the rotor caused by dry particles that get trapped between the rotor and housing. Generally, this offsetting results in empty pockets filling to about 60 percent capacity, with this type of valve often used for materials like peanuts and sunflower seeds.
Depending on the exact product and application, a rotary airlock valve can be made more robust to handle harsher materials or difficult applications. For heavy-duty models, bearings on the end plates are usually placed outboard, or away from the product contact zones.. Additionally, many valves utilize air purge fittings to prevent contaminants from escaping past the seals, as is the case with certain blow through or drop through models used in conjunction with a positive internal pressure. Certain manufacturers also make rotary airlock valves designed to provide easier access to internals for easier cleaning and maintenance.
Why Rotary Airlock Valve Maintenance Is So Important
Regular maintenance is key to ensure an efficient and long lifespan for a rotary valve. Airlocks or valves should also undergo frequent inspections to keep systems running optimally. Common issues like air leakage, clogging, and preventable wear can be avoided by correctly maintaining rotary airlock valves. Not doing so can lead to diminished efficiency, while downtime is more likely due to unplanned maintenance or repairs.
Keeping rotary airlock valves in good condition requires a solid maintenance plan and an inventory of critical components. With proper upkeep, major rotary airlock valves and connected equipment failures can often be avoided. This, in turn, makes facilities more productive, as they can keep product flowing, make work environments safer, lower operational costs, and prolong equipment lifespans.
Best Practices & Tips on Rotary Airlock Valve Maintenance
It’s important to follow certain best practices when maintaining rotary valves or airlocks. A processing facility often gets tips from the valve’s manufacturer, which will help keep material handling systems running smoothly and prevent unnecessary downtime.
Interior Inspection
During processing, bulk powders flow continuously through the rotary valve. Airlock endplates, housings, rotors, and rotor blades must be inspected to ensure they remain in good operating condition. Depending on the manufacturer and model, this may simply involve accessing internal components through an access door for this purpose. Other types of rotary airlock valves may require partial disassembly instead. If damage is noted, valve parts should be repaired or replaced immediately.
Examine Shaft Bearings & Seals
A thorough examination of the rotor shaft support bearings should be conducted to ensure efficient operation, noting whether there’s too much play. Bearings should be regularly replaced so they don’t become overly worn, as this can affect the position of the rotor in the housing and lead to damage should metal contact metal due to the machine’s tight tolerances. At least once per month, shaft seals should be carefully examined for leaks. The gland retainer on the packing seals should be tightened, while seals should be replaced before they look too worn. When looking at air-purged seals, keeping the rotary valve’s shaft seals properly air-purged by ensuring the air purge is turned on whenever the internal pressure acting on the valve is present.
Tighten Rotor Tip Clearances
Regardless of the rotary valve type, airlocks need to be extremely tight for the clearances on their rotor tips. This is due to the need to control the flow of powders between areas with substantial pressure differentials. It’s important, therefore, to avoid any potential issues because of too much air leakage.
To keep these clearances tight, the following steps should be taken:
- Lock out power to the valve’s motor.
- Models with connections on the valve’s bottom or top that allow removal should have them removed to allow access for servicing.
- Clean product residue and other contaminants from the valve’s interior.
- Insert feeler gauge to ensure a minimum clearance between the head plate on the valve’s drive end the rotor vane’s end.
- Slide gauge down to the rotor’s shaft, before moving it toward the tip.
- Should the gauge catch, clearances are too tight at that point.
- If the issue is due to damage, sanding or hand filing can loosen the tolerances, though care must be taken not to remove too much material.
- Repeat the process on the valve’s blind end, then repeat the process for all vanes.
- Slide the feeler gauge between the housing bore and the rotor’s tip, moving it between head plates.
- To check rotor vane tip clearances, rotate the rotor as it normally moves during operation.
- Using a gauge that’s .001 inch larger than the maximum suggested clearance, it should be slid into the same areas.
- If the gauge fits into these spaces, it shows enough wear to the valve to create sealing problems.
Should any parts examined appear too worn, it’s essential to replace them to ensure proper tolerances.
Lubrication of Drive Components
As with any drive system, the rotary airlock valve’s motor should always remain properly lubricated. This helps avoid any deterioration, including the drive chain and speed reducer. The oil level in the gearbox should be tested to ensure it remains adequate, while the lubricant should be changed according to manufacturer guidelines. If outfitted, the sprockets and chain should receive frequent lubrication. If the owner's manual isn't clear enough, the supplier can offer information on the valve’s recommended intervals for lubricating it.
Drive Chain & Sprocket Adjustments
During inspection, checking whether the drive train has the proper tension and the sprockets are aligned is essential. Adjustments should be made if necessary, though the drive chain’s guard should be in place before any maintenance.
Contact Detection Systems
Contact detection systems can be added to a rotary airlock valve to alert operators when conditions, where the rotor can contact the housing, are likely to occur, which can damage the unit. By monitoring this area between the rotor and the housing, operators are alerted when contact between the rotor and housing happens. This helps keep metal contamination out of products, preventing potential valve damage.
Proper Training
Performing maintenance correctly requires proper training. At the same time, it’s important to have a preventive maintenance plan, as not performing maintenance appropriately results in poorer equipment performance and lowers the lifespan of a rotary valve. Airlocks and feeders are sensitive devices, so only trained staff must be tasked with maintenance.
This training should familiarize any employee involved in its maintenance or operation with the specific rotary airlock valves used by the facility. This includes any worker charged with cleaning the unit so that it’s properly disassembled and reassembled so as not to damage housing surfaces or rotor tips. Some makers of rotary airlock valves will even provide routine training to ensure their products are used and maintained appropriately.
Prater Rotary Airlock Valves
Prater Industries manufactures six basic types of rotary valve or airlock.
These are:
- Heavy-duty PAV rotary airlock valve: Able to handle higher temperatures up to 500°F (260°C), these valves work well for corrosive and abrasive materials processed under harsh conditions.
- Abrasion-Resistant rotary airlock valves: Using cutting edge alumina ceramic coatings that offer superior abrasion resistance, these rotary valves are built to last longer and perform better while also requiring less maintenance.
- Quick-Take-Apart (QTA) rotary airlock valve: Offering easy access to the rotary airlock valve’s internal components to ease maintenance, Prater’s QTA series can be easily cleaned like the BAV series though with a smaller footprint than the railed model.
- BAV rotary airlock valve: With the rotor on a rail system that easily demounts and allows access to internal components for maintenance without the need for tools, Prater’s BAV rotary airlock valve works well for applications that require frequent and quick cleaning.
- Blow-Thru rotary airlock valve: This rotary airlock's larger rotor pockets make it perfect for use with pneumatic conveying lines. They also enable it to operate at a lower speed to reduce wear, increase efficiency, and lower maintenance costs.
- Dust Collector rotary airlock valve: Designed for cyclones, dust collectors, and hoppers, these basic valves have maintenance-free in-board bearings with larger pockets and a fixed speed drive designed for function as an airlock under limited pressure differential.
To learn more about maintenance for our rotary airlock valves and other material handling equipment, contact the experts at Prater today.
