Engineering for Predictable Feed: Why the Dual Rotary Valve System is Required for Consistent Metering

The Unpredictable Challenge of Railcar Unloading

In large-scale material transfer operations, achieving a consistent flow rate is critical for system reliability. When unloading material like cement from gravity railcars, engineers face inherent material handling challenges. Railcar hoppers are notoriously shallow-sloped, which can lead to bridging and restricted flow, making conveying rates highly unpredictable.

For a high-capacity transfer, a simple, single system is insufficient to handle these erratic feed characteristics. Delta Ducon’s engineered solution is a dual-stage vacuum-to-pressure system that prioritizes redundancy and precise metering to ensure a reliable feed into the long-distance transfer line.

Stage 1: The Dual-Vacuum Pickup and Separation

To counteract the unpredictable flow from gravity railcars, the system is designed to attack the source of the material at two independent points.

• Redundant Pickup: The design features two independent vacuum systems operating in parallel to vacuum product from two outlets on the railcar, mitigating the risk of total stoppage if one flow is restricted.

• Separation and Collection: Each vacuum system feeds into its own Collector Filter, a pulse jet style unit, which separates the conveyed material from the motive air. This stage cleans the air before it reaches the vacuum blower and prepares the material for the next critical step: metering.

Stage 2: The Dual-Rotary Valve Metering Bridge

The most critical engineering component of this system is the bridge between the vacuum side (pickup) and the pressure side (long-distance transfer). This is where material flow is stabilized and made predictable using dual rotary airlocks.

• Airlock Function: At the discharge of each collector filter, a dedicated 14" XL PERMA/flo Rotary Valve is supplied to meter the collected product into the single common pressure conveying line. These valves serve a dual purpose: they meter the material flow and act as an airlock, sealing the high vacuum/low pressure side from the high-pressure transfer side.

• Severe Duty Metering: Since the material can be abrasive, the reliability of the rotary valve seal is paramount. The PERMA/flo line of rotary valves is considered severe duty because the rotor and inlet shoe are cast from a hard alloy with a hardness of 500-600 BHN. This is a solid alloy casting, not a superficial surface hardening that will wear away and expose softer metal, guaranteeing the seal integrity required for efficient, long-term metering.

• The Predictable Feed: By using two rotary valves operating in concert, the system ensures that even if one vacuum pickup or one airlock briefly fluctuates, the overall transfer rate remains consistent, creating the predictable feed necessary for stable pressure conveying.

Stage 3: High-Capacity Pressure Transfer

The metered material is then conveyed through a common pressure system (230 feet horizontal, 80 feet vertical) powered by a robust 150 HP positive displacement blower.

• Abrasive Wear Control: To handle the wear in the conveying line (which includes 3 equivalent 90 degree bends), PERMA/flo Abrasion Resistant Elbows are included. These elbows are a heavy cast alloy with a hardness of 400-450 BHN, ensuring they withstand the abrasive action of the particles.

• System Integration: The entire process is designed for optimal performance, culminating in the discharge into a storage silo via an Targetbox. The reliability of this complex process is managed by an engineered written sequence of operation that can be integrated into an optional PLC-based control panel.

  
  

Conclusion

For high-capacity, high-abrasive applications like cement railcar unloading, an off-the-shelf component or a simple single-stage system is a risk. Delta Ducon’s dual vacuum-to-pressure engineered system—anchored by the severe-duty PERMA/flo Rotary Valves and Abrasion Resistant Elbows—is the proven solution to overcome unpredictable material flow, guaranteeing stable metering and maximum system uptime.