Case Study - Extreme Durability: Quadrupling Rotary Valve Life in a Marble Processing Plant

A Case Study by Delta Ducon

1. Executive Summary: The Challenge of Abrasive Marble Dust

In the demanding world of mineral processing, the phrase "rotary valve wear" is often synonymous with costly downtime, frequent maintenance, and frustratingly short equipment life. A prominent marble processing plant in the southern United States faced this exact predicament. Their process, which involved pneumatically conveying highly abrasive marble dust, was hampered by the rapid failure of their existing rotary valves. These valves, which were a critical link in their dilute phase conveying line, were being discarded every few months due to extreme wear. In 2020, they turned to a trusted partner, Delta Ducon, to find a solution. Leveraging a previous, successful collaboration from 2004, Delta Ducon's engineering team investigated the root cause of the failures and offered a robust solution: the PERMA/flo™ Extreme Rotary Valve. This case study details how this purpose-built valve, designed for durability and ease of maintenance, not only solved the immediate wear problem but also quadrupled the life of the customer's rotary valves and became the standard for their entire fleet.

2. The Problem: A Vicious Cycle of Wear and Disruption

The marble processing plant's operational headaches stemmed from a combination of material properties and equipment design flaws. Marble, chemically similar to calcium carbonate, contains a high silica content, making its dust extremely abrasive. When ground to a fine powder and transported through a dilute phase conveying line, this material acts like a high-speed sandblasting medium, relentlessly attacking any surface it contacts.

The plant's existing rotary valves were fundamentally unsuited for this severe-duty application. Delta Ducon's investigation identified several key issues:

• Excessive Rotor Speed: The rotary valves were running at extremely high speeds to keep up with the demands of the dilute phase conveying line. While this fed the process, it dramatically accelerated the wear and erosion of the valve's internal components.

• Widespread Component Erosion: The rapid movement of the abrasive material led to severe wear on multiple critical parts. The rotor tips, responsible for creating the air seal and carrying material, were the first to fail. This was followed by erosion of the housing interior, the shaft, the end covers, and the packing area at the stuffing box.

• Lack of Adjustability and Repairability: The previous vendor's valves were a "throwaway" component. With no provisions for field adjustment or in-place repair, once a valve began to fail, the only solution was to replace it entirely. This resulted in the plant continuously purchasing and replacing expensive valves every few months, creating a significant and unsustainable operational cost.

• Impeded Material Flow: The inadequate design of the old valves allowed "blow back" air from the conveying line to escape through the valve's inlet. This created a positive pressure area that disrupted the material flow from the hopper, leading to inconsistent feeding and process instability.

  
  

The combined effect of these issues created a vicious cycle of maintenance and replacement. The plant was trapped, unable to achieve consistent production rates without constantly stopping to replace or repair failed equipment.

3. The Solution: The PERMA/flo™ Extreme Rotary Valve

Delta Ducon, a company with over a century of experience in bulk material handling, has been providing high-performance products since 1964. Their reputation is built on a commitment to quality and innovation, and their extensive product line is specifically renowned for its ability to handle all types of dry bulk materials, including those that are abrasive, severe, or difficult to manage. With a deep understanding of the plant’s history and a successful past installation, Delta Ducon offered a definitive solution: the PERMA/flo™ Extreme Rotary Valve.

The Extreme Rotary Valve, which can function as a rotary feeder or an airlock, is not a modification of a standard valve. It is a purpose-built component designed from the ground up to withstand the harshest operating conditions. Its unique design and features directly address every issue the marble processing plant faced:

• Superior Material Construction: The core components—the rotor and the seal/wear shoe—are constructed of a special chrome-iron alloy called P-33. This material is far superior to surface-hardened metals. Unlike other valves where a thin hardened layer can wear off to expose a softer metal base, P-33 is a solid alloy casting that yields a robust hardness of 500-600 Brinell throughout. This ensures that the valve maintains its incredible abrasion resistance even as the surface wears, providing unparalleled longevity.

• External Field Adjustability: The PERMA/flo™ Extreme Rotary Valve features a unique design that offers external field adjustment between the rotor and the seal/wear shoe. This eliminates the need for disassembly and allows technicians to easily restore the valve's crucial internal clearances without removing the housing from the process line. This feature alone drastically reduces maintenance time and extends the valve's operational lifespan. Furthermore, both the rotor and the wear shoe can be replaced in the field with the housing in place, offering a level of repairability that was absent in the old valves.

• Integrated Venting Solution: To solve the problem of "blow back" air disrupting material flow, Delta Ducon included a properly designed venting solution as part of the offering. This system diverts the excess air from the convey line to a customer-supplied vent source, ensuring consistent and smooth material feeding from the hopper.

• Upgraded Shaft Seal Package: To address the rapid wear in the packing area, the PERMA/flo™ Extreme Rotary Valve was fitted with an upgraded shaft seal package. This high-quality seal minimizes leakage at the stuffing box and limits overall maintenance, further contributing to the valve's long life and the plant's operational efficiency.

  
  

The Extreme Rotary Valve is available in both a standard version (rated up to 500°F) and a High Temp version (rated to 800°F with occasional spikes up to 1000°F), making it versatile for a wide range of industrial applications.

4. Results and Long-Term Success

The installation of Delta Ducon’s PERMA/flo™ Extreme Rotary Valves in 2020 marked a significant turning point for the marble processing plant. The immediate results were dramatic and exceeded expectations:

• Quadrupled Valve Life: The previous valves lasted only a few months. Since their installation, the Delta Ducon valves have already lasted four times longer than the previous vendor’s products and continue to operate flawlessly. This massive increase in equipment life has led to a significant reduction in replacement costs and a substantial improvement in maintenance efficiency.

• Improved Process Conditions: The integrated venting solution and the valve's consistent feeding capabilities have eliminated the flow disruptions caused by blow back air. This has resulted in more stable and reliable process conditions, allowing the plant to maintain a continuous, uninterrupted production line.

• Fleet-Wide Adoption: The success of the initial installation was so profound that other plants within the customer’s fleet have also upgraded to the PERMA/flo™ Extreme Rotary Valve. This fleet-wide adoption serves as a powerful testament to the valve's proven efficacy and reliability in a highly demanding application.

  
  

Delta Ducon's commitment to providing robust, durable, and easy-to-maintain solutions has solidified its position as a trusted partner in the industry. As a leading manufacturer and supplier of bulk material handling systems and components, including products like PERMA/flo Pipe & Fittings, KG Diverters, and SPIRA/flo Pipe for Plastics, Delta Ducon is a proven provider for industries ranging from mining and minerals processing to cement, steel, and power. The marble processing plant's success story is just one of many examples of how Delta Ducon’s high-quality products, backed by over 100 years of experience, consistently exceed client expectations.