The Clarkson Co. used Algor's Mechanical Event Simulation software to simulate the valve in action on a computer, reacting to the severe pressure and temperature of the slurry piping system's flowing materials.

The Clarkson Co., a family-owned design and manufacturing company in Sparks, Nev., supplies a key component, a knife-gate valve, that controls the flow in many of the piping systems around the globe. The company, which introduced its first knife-gate valve in the 1970s, is studying its latest generation of products to find ways of adapting them to serve better under the various conditions its customers face.

Mining companies use piping systems to transport newly mined minerals, such as gold, ore, and coal, to processing plants. The excavated materials are crushed and suspended in a liquid medium, generically called slurry, for easy flow. An efficient slurry handling system is crucial to timely mineral processing, which is necessary for fast delivery to a worldwide market.

The slurry flow can be very abrasive and corrosive to the hundreds of valves directing its materials. In mining, newly crushed ore has a sharp surface, can be quite hot, and flows quickly, constantly, and often at high pressure. A slurry valve must be designed for these conditions to reduce maintenance time and replacement costs.

Power companies, meanwhile, pipe different materials, putting their own set of demands on the line' components. Using software developed by Algor Inc. of Pittsburgh, Clarkson has simulated its valve in action to test how variations in material and design of the product will hold up under different pipeline stresses.

Clarkson, which has marketed products to the metal and mineral processing industries for more than 65 years, created a unique type of slurry valve in the 1970s, the KG Series knife-gate valve. The company designs and manufactures knife-gate and control valves that can quickly halt and isolate sections of a slurry flow. Efficient control is necessary when the slurry must be delayed, inspected, or redirected. Companies that use Clarkson equipment include Newmont Gold Co., Taiwan Power Co., and International Paper. Clarkson knife-gate valves are also used in other applications, including industrial scrubber systems, wastewater treatment systems, and industrial process water systems. About half of Clarkson's products are exported.

The original KG Series knife-gate valve has been refined over the past two decades. The latest designs, Series KGD, are referred to as "wafer-type" valves because they are lighter and thinner than their predecessors, although they can handle higher pressures. The narrower valve fits tighter spaces and gives pipeline designers more flexibility. Wafer-type valve dimensions meet a nationwide standard, providing greater flexibility in choice of supplier because the valves are interchangeable.

The knife-gate valve has a blade-like steel gate that lowers into the slurry flow to create a bubble-tight seal. The valve has two matching, smooth elastomer sleeves that seal the blade when the gate is closed and seal each other when the valve is open, so the slurry can flow through unobstructed. The elastomer sleeves are designed to resist abrasion and corrosion and to cover the valve's metal parts to shield them from wear.

The knife-gate valve was a new concept when it was introduced because it replaced conventional metal seats and gate guides with easily replaceable snap-in elastomer sleeves, which are more durable and versatile, and handle higher pressure and temperature. Conventional metal seats and gate guides can fill with hardened slurry and then fail to open or close.

Pipeline operators value the elastomer's long life because each seal costs between $75 and $500 to replace. More important, they lose revenue when they suspend the slurry system for maintenance repairs.

Clarkson wanted to develop a greater variety of elastomer seals for the wafer-type valve to increase its efficiency and reliability in different applications. For example, power companies prefer synthetic types of elastomers like neoprene, butyl or viton, which handle high temperatures and corrosive materials, while mining companies prefer elastomers like natural gum rubber for abrasive slurries.

To increase its efficiency in different applications, a greater variety of elastomer seals for the wafer-type knife-gate valve were developed.

The company had been able to recommend to customers seals made from various elastomers, but its judgment was based on published data and past trial and error in the field. Clarkson wanted to give its customers more scientifically supported suggestions by testing the elastomers in a laboratory. But molding prototypes is expensive and takes weeks. Engineers decided to test virtual prototypes on the computer.

Nick Williams, a project manager in Clarkson's engineering services department, used Algor's Accupak/VE Mechanical Event Simulation software for virtual prototyping with linear and nonlinear analysis to test different elastomer materials for the seal of the wafer-type valve. The software predicted how various nonlinear elastomer materials respond to loading conditions like the slurry's heat and pressure.

Accupak/VE combines traditional finite-element analysis with the physics of time, motion, and impact to determine the development and outcome of linear and nonlinear events. Engineers insert known physical data, such as weight and directional movement, into the program, but don't need to specify force because stresses in Algor's mechanical event simulation are calculated based on the physics operating during the event.

Clarkson's product development team designed a steel knife-gate model and an elastomer seal model using CoCreates H.P. Solid Designer CAD software. In preparation for mechanical event simulation, Williams used Algor's Houdini product to convert the CAD solid models into one 3-D solid brick finite-element model. He inserted contact elements between the elastomer and the steel.

Williams used Algor's Merlin Meshing Technology to refine the surface mesh. He specified a coarse mesh in parts of the seal he knew were inconsequential to the load applications and omitted small, irrelevant features. Analyzing fewer elements reduced processing time, but still produced an accurate analysis. Williams later used Houdini to refine the mesh in areas that indicated high stress in the analysis, such as the points where the sleeves seal the knife-gate.

Williams set boundary conditions to constrain the seal's four corners, replicating its attachment to the valve body and neighboring pipe flanges. Then he applied a load curve based on previous physical testing data that represented the rise in pressure in a pipeline. In additional analyses, he applied pressures specified by the American National Standard Institute, which requires that the elastomer in the valve withstand pressure one and a half times its maximum operating pressure. He also applied prescribed displacement to move the knife-gate, which would cause displacement in the seal.

Algor's Monitor utility tracked the progress of each event simulation to help identify problems during analysis. "I can terminate an analysis immediately if the Monitor utility indicates that the elastomer material will fail in its current conditions," said Williams. "I saved many hours and even days of processing each time this occurred."

The elastomer material's deflection was also considered. Williams had designed holes in the elastomer sleeve to give it an area in which to deflect. He wanted to be certain that the material moved into these areas when the loads were applied.

With the computer simulations, Clarkson could determine which elastomer candidates had a high probability of success without performing numerous and costly physical tests.

"We felt we were compromising important data with limited linear analysis," said Williams. "We are now more comfortable manufacturing a prototype. Plus, we are saving time and have a smaller margin of error."

Williams and the Clarkson product development team are still working to improve the wafer-type valve. They continue to study current elastomer options and explore other elastomer materials, and intend to use computer simulations to help develop advanced knife-gate and control valves for use in all types of slurry handling systems.

This article was prepared by staff writers in collaboration with outside contributors.

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