Maintaining an airtight bulk solids processing or handling system is essential for both operational efficiency and worker safety. Choosing the right airlock valve can help maintain a steady material flow rate while preventing costly air leakage and pressure drops. The double flapgate airlock valve, particularly, is highly effective for applications involving abrasive materials or high-pressure and high-temperature environments.
While the rotary airlock valve is commonly used in solids processing systems, it requires frequent maintenance and replacement, especially when handling abrasive materials or operating under extreme conditions. The double flapgate airlock valve offers a more durable solution in such cases. Unlike rotary valves, double flapgate valves are designed to seal completely and are less prone to wear, making them ideal for demanding industries such as cement, chemical processing, pulp and paper, mining, power generation, and more.
How the Double Flapgate Airlock Valve Works
The double flapgate airlock valve is available in various configurations tailored to specific needs, including high-pressure, high-temperature, and abrasive material handling. Its design is simple and features few moving parts. The valve consists of:
- A housing with an inlet at the top and a discharge at the bottom
- Two gates
- Two seats (top and bottom) where the gates close
- A center chamber between the gates
- Pivoting arms for each gate
- Pneumatic actuators or counterweights to open and close the gates
Materials used in constructing the valve are chosen based on the application. For instance, the valve’s housing is often made from cast iron, while gates and seats may be made from stainless steel or white iron/Ni-hard.
Operation Process
Material Inflow: The inlet fills with material
Gate Opening: The top gate swings down to allow the material into the center chamber between the gates
Top Gate Sealing: The top gate shuts to seal the valve, stabilizing the pressure
Material Discharge: The bottom gate opens, allowing the material to flow out through the discharge
The sequential movement of the gates ensures a consistent seal, preventing air leakage and maintaining pressure balance between upstream and downstream equipment.
Gate Operation
Typically, each gate is powered by a pneumatic actuator, which is controlled by a solenoid valve linked to a timer or PLC system. This setup ensures precise opening and closing of the gates, providing a steady material flow rate. Alternatively, a counterweight mechanism can be used, especially when electricity is unavailable or when precise flow control is less critical. However, counterweights operate more slowly and may result in uneven flow rates.
Applications to Avoid
Despite its advantages, the double flapgate valve may not be suitable for all situations. For example, it should not be used at the bottom of a material column, such as a bin or hopper, as the material’s weight could prevent the valve from closing properly once the top gate opens. In such scenarios, a rotary airlock valve would be a better choice. Additionally, the double flapgate valve has a lower flow rate compared to rotary valves, typically 2 to 5 times slower, which can limit its use in applications requiring high flow rates.
Benefits for Challenging Applications
Although the double flapgate valve comes with a higher initial cost than a rotary valve, it offers significant long-term benefits in challenging applications. It reduces maintenance downtime, labor costs, and the frequency of valve replacements, offering an excellent return on investment. Here’s a closer look at how the double flapgate valve excels in demanding environments:
Abrasive Materials
In pneumatic conveying systems handling abrasive materials, rotary valves often need to be replaced multiple times a year due to wear. The constant rotation of the rotor subjects the valve to significant wear. However, with the double flapgate valve, wear is localized to the gates and seats, which are easier and cheaper to replace. This valve can last longer, typically requiring only gate and seat replacements within a year, making it a more cost-effective solution in the long run.
High Pressure
For high-pressure applications, the double flapgate valve’s housing, made from cast iron or stainless steel, ensures durability. Additional arms and actuators can be added to improve gate sealing, especially for pneumatic conveying applications with differential pressures exceeding 7 psi.
High Temperature
In high-temperature environments (over 700°F), the valve’s components can be constructed from stainless steel to ensure a long lifespan. Unlike rotary valves, which may experience seal issues due to thermal expansion and contraction of rotating parts, the double flapgate valve’s minimal moving parts maintain a secure seal even under extreme temperatures.
Handling Large Material Chunks
One of the advantages of the double flapgate airlock valve is its ability to handle larger material chunks without causing blockages. Rotary and other airlock valves can clog when large particles are introduced, leading to downtime and expensive repairs. The double flapgate valve, with its 8- to 12-inch square openings, can pass larger material pieces, preventing such issues.
Low Maintenance and Longevity
The double flapgate valve requires minimal maintenance due to its simple design and fewer moving parts. Its housing can last for over 20 years without needing replacement. The gates and seats, which are typically subject to wear in abrasive applications, can be easily replaced, making maintenance straightforward and cost-effective. The frequency of replacement depends on the material being processed. It’s recommended to inspect the valve annually, particularly in pneumatic conveying systems, to ensure a proper seal. If a pneumatic actuator is used, the cylinders may need replacement based on workload demands.
In conclusion, the double flapgate airlock valve provides a reliable, low-maintenance solution for handling abrasive materials and operating under high-pressure or high-temperature conditions. Its long service life, minimal wear, and ability to handle tough applications make it a valuable investment for industries requiring consistent and efficient material handling systems.
