Case Study - A Solid Solution to a Rocky Problem: How Delta Ducon's Extreme -Duty Rotary Valves Solved National Gypsum's Discharge Challenge

Introduction: The Painful Problem of Passing Stones

In the world of industrial manufacturing, a seemingly simple problem can quickly become a costly and frustrating ordeal. For National Gypsum's Burlington, New Jersey plant, the challenge was to efficiently discharge a mix of gypsum rocks and fine powder from their 300-ton capacity storage silos onto a conveyor belt. The material—composed of brittle, chalky gypsum rocks up to 2 inches in diameter and extremely fine powder—presented a dual-natured problem that standard equipment simply couldn't handle.

The plant, a major manufacturer of wallboard for residential and commercial construction, had invested in these silos to ensure continuous operation, even during routine maintenance of upstream equipment like their rock-drying system. However, this critical part of their process was crippled by a persistent discharge problem. The wrong equipment meant constant jamming, flooding, and expensive downtime. The plant was ready to give up on its silo system entirely, but a new approach and the right partner would soon prove that passing stones could, in fact, be a very good thing.

The Initial Attempts: A Series of Costly Failures

The plant's first attempt at a solution was to replace its old, worn-out rotary valves. The existing valves were so old that replacement parts were no longer available, and their worn state made them ineffective at controlling the material flow. National Gypsum chose new, heavy-duty 22-inch valves with a conventional cast-iron body and a fabricated, open-bladed rotor, believing that their adjustable abrasion-resistant tips would provide long wear life. Unfortunately, this was not the case.

The very first test revealed a critical design flaw for this specific application. The large gypsum rocks would enter the valve, fill the rotor pockets, and immediately jam the rotor. The motor, trying to force the rotor to turn, would hit a high amp load and trip out, bringing the entire line to a halt. In an effort to overcome this, operators increased the motor's horsepower and the drive sprocket size. The result was even more dramatic and destructive: the drive shaft itself twisted and broke, leading to even more downtime and repair costs.

In a desperate move to salvage the situation, the plant adjusted the rotor tips to increase the clearance. While this seemed logical on the surface, it only solved one problem by creating another. The larger gap allowed the fine gypsum powder, which made up a significant portion of the material, to flood around the rotor tips and into the feeding process. This flooding led to further maintenance nightmares and more production downtime. After many hours of frustration, the plant realized these valves were simply not up to the job.

Still determined to utilize the silos for continuous operation, the plant then sought a completely different solution: a vibratory tube conveyor. While this system successfully handled the rocks, it failed to address the powder problem. The fine gypsum dust would fluidize and flood the process, once again forcing a shutdown. This last effort proved so discouraging that the plant completely abandoned the silos and went back to running its dryer and other upstream equipment continuously, sacrificing essential preventive maintenance in the process.

A New Hope and a Confident Partner

Just as hope was fading, the plant hired a new plant manager with a fresh perspective. Having come from a company that produced charcoal briquets, he had firsthand experience with a extreme-duty rotary valve that had proven successful in handling similarly varied sizes of charcoal. He thought, with a glimmer of hope, that perhaps this valve could be the answer for the gypsum plant.

Ironically, this very same valve had been a contender during the plant's initial selection process, but it had been passed over due to its higher cost. Now, after two costly failures, the plant was no longer focused on budget but on finding a solution that actually worked. The plant manager contacted the supplier, Delta Ducon, a premier pneumatic conveying company known for its focus on highly abrasive and difficult-to-handle materials. The confidence of the Delta Ducon team was immediate and unwavering.

To prove the valve's capability, the plant manager shipped 500 pounds of gypsum to Delta Ducon’s testing facility, including large 2-inch rocks and the problematic 200-mesh fine powder. The Delta Ducon engineers, experts in pneumatic conveying systems, meticulously tested the material in their extreme-duty valve, experimenting with different inlet configurations to ensure a perfect flow. Once they were satisfied, they made a compelling offer to the National Gypsum plant manager: "You let us put one of these valves in for sixty days, and if it doesn't work, you don't pay for it." With nothing to lose and everything to gain, the plant manager eagerly accepted the trial.

Delta Ducon's Engineered Excellence: The PERMA/flo Solution

The solution provided was the 18-inch PERMA/flo Extreme Duty “18 XL” rotary valve, a testament to Delta Ducon's superior engineering for abrasive applications. This 400-pound beast was designed from the ground up to solve the very problems National Gypsum was facing.

Unlike the conventional valves that failed, the PERMA/flo valve features a robust cast-iron housing and a closed-end rotor cast from Ni-Hard, an exceptionally hard iron alloy with a 550 Brinell hardness. This incredibly durable material means the rotor’s abrasion resistance never wears off, eliminating the need for delicate coatings. The closed-end design is a critical feature, preventing the fine powder from filtering between the rotor ends and the housing, which was the source of the flooding issues.

Additionally, the valve's design ensures the rotor has no contact with the valve housing. Instead, the only point of contact is with an adjustable wear shoe. This innovative design allows material to enter only the pockets directly under the valve inlet. As wear inevitably occurs over thousands of hours of use, the rotor and shoe can be quickly and easily adjusted from external set points to bring the clearance back to factory settings. Delta Ducon’s vice president, noted, "You should never have to buy another valve. It's just the shoe that will wear out after thousands of hours of use, so you might have to replace the shoe." This longevity and ease of maintenance are a hallmark of Delta Ducon’s extreme-duty valves.

Perhaps the most crucial custom feature for this specific application was the V-shaped AR-steel breaker bar installed in the valve’s inlet. This ingenious modification, developed during the testing phase, prevents the large rocks from jamming between the rotor and the wear shoe. As Delta Ducons President describes, it acts "like a plow," shearing any rocks that hit dead-on center to the left or right, ensuring continuous flow.

Beyond the robust physical design, the valve's functionality is also state-of-the-art. It is driven by a variable-speed motor and a chain and sprocket system, protected by a safety-yellow OSHA cover. This variable-speed drive, controlled by a PLC with an easy-to-operate control panel, allows the plant to precisely control the gypsum's discharge rate, creating a continuous material flow that matches the mill’s consumption. Furthermore, the PLC automatically activates a reversing sequence if it senses a jam or amperage spike, a feature that prevents the very kind of catastrophic failures that plagued the previous valves. The PLC also collects valuable usage data, helping the plant maintain accurate inventory records.

Success at Last: A Partnership for the Long Term

The moment the first Delta Ducon PERMA/flo Extreme Duty valve was installed and put online in early 2005, it worked exactly as planned. The variable-speed drive and the custom-engineered V-breaker bar ensured that both the large rocks and the fine powder discharged evenly and consistently, with no jamming or flooding.

Wayne Vetter, the Burlington plant engineer, was thrilled with the outcome. "We were really pleased," he says. "The supplier was good to work with. This wasn't a standard application." The success of the initial valve was so profound that the plant quickly purchased three more, ensuring they would have two for each of their silos. While the silos are temporarily offline for the installation of a heated dust collection system, the plant is confident in the future. As Vetter says, "We were happy with the extreme-duty valves, and I know we're going to be even happier when we have both silos up and running and passing stones again."

The partnership with Delta Ducon, built on expertise, confidence, and a commitment to providing a tailored solution, proved to be the key to overcoming National Gypsum’s most persistent material handling challenges. Delta Ducon’s comprehensive approach to solving complex engineering problems and their focus on durable, long-lasting products make them a leading provider in the industry. To learn more about how Delta Ducon can help solve your most difficult material handling challenges, explore our engineering capabilities.

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