Common Troubleshooting

Troubleshooting Common Rotary Airlock Valve Issues:

A Guide to Diagnosis and Solutions

The rotary airlock valve is a crucial component in any pneumatic conveying system, ensuring the efficient transfer of materials between vessels with minimal air leakage. When problems with the valve arise, knowing how to troubleshoot can save time and money and prevent costly downtime. This guide explores how to identify and resolve the most common issues with rotary airlock valves, including jamming, excessive air leakage, noisy operation, and insufficient material throughout.

Understanding the Rotary Airlock Valve

A rotary airlock valve typically consists of several key components: the housing and headplates (forming a cylindrical cavity with material inlet and outlet), bearings supporting the rotor and blades (or vanes), and shaft seals. The rotor spins inside the housing, creating pockets between adjacent blades that carry a fixed volume of material from the inlet to the outlet.

Valves come in various configurations to handle specific materials and operating conditions, including:

Rotor Configurations

Typically featuring 6, 8, or 10 blades, with adjustable blade-to-housing and blade-to-headplate clearances.

Housing Types

Drop-through, side-entry, and blow-through styles, each suited to different materials and processes.

Functionality

Rotary airlocks can function as an airlock, a feeder, or a combination of both, depending on your system’s requirements.

Choosing the Right Valve to Prevent Problems

Many operational issues stem from improper valve selection. To prevent these issues and avoid these common pitfalls, we recommend the following:

Material Properties

Selecting a valve based on the material’s bulk weight, particle size, moisture content, or potential to corrode or ignite is crucial. For example, moist air can cause materials like powder to clump, which may jam the valve.

Operating Conditions

Consider the pressure, temperature, and other system characteristics. If conditions change—such as a drop in temperature or the introduction of moisture—these can affect valve performance.

Temperature Considerations

Elevated material temperatures can cause valve components, especially the rotor, to expand, affecting clearances and potentially causing jams. In such cases, you may need to adjust the valve’s clearances by disassembling, machining, and reassembling the rotor.

Excessive Air Leakage

All rotary airlock valves allow some degree of air leakage due to the necessary clearances between the rotor and housing. However, excessive leakage can hinder performance and reduce throughput. It’s important to discuss leakage tolerances with your manufacturer to ensure your valve is suited to your application’s pressure differential and operating temperature.

There are two types of air leakage:

This occurs in the space between the rotor blades and the housing. It tends to decrease once material enters the valve.

Air enters the rotor pockets as they pass the material outlet, and this increases with the valve’s operating speed.

To minimize air leakage, consider installing flexible seal strips or selecting a valve with additional rotor blades to reduce clearance. You may also need to install vents in the housing or headplate.

Troubleshooting and Fixing Common Problems

1. Jamming

Jamming occurs when material becomes lodged between the rotor blades and the housing or headplates, often due to oversized material or an incorrectly sized valve. Here’s how to address it:

Check Rotor Direction and Movement:

Ensure the rotor is spinning smoothly and not in contact with the housing. Shuddering or unusual noise can indicate material blockage.

Adjust Blade Tips:

Beveling or relieving blade tips can reduce the chances of material getting caught. Installing flexible seal strips can also help prevent material from being pinched between the blades and housing.

Inspect for Foreign Objects:

Sometimes, tools or debris can enter the valve and cause a jam. Ensure that any found object is properly removed, and investigate how it got there to prevent future issues.

Material Changes:

If material properties have changed, like moisture content or size, this may affect flow. Adjusting the valve or material flow may resolve the issue.

2. Noisy Operation

While some noise is expected during valve startup, excessive noise is usually an indication of underlying issues:

Rotor-to-Housing Clearance:

Noise may occur when material, especially fines, gets caught in the clearances. Coating the valve interior with resistant materials like nickel or chrome can reduce buildup and noise.

Moisture or Hygroscopic Materials:

If the material absorbs moisture, it can create a buildup inside the valve. Installing a dehumidification system for the air or venting moisture before it reaches the valve may alleviate the issue.

Check for Rotor Expansion:

High material temperatures can cause the rotor to expand, reducing clearances and leading to contact with the housing. If this is the case, follow the previously mentioned steps to manage temperature fluctuations.

3. Insufficient Material Throughout

Check for Air Leakage:

Ensure the rotor is spinning smoothly and not contacting the housing. Shuddering or unusual noise can indicate material blockage.

Reevaluate Valve Size: