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Molding Replaces Cast Brass Valve

Molding Replaces Cast Brass Valve

Conversion of a water control valve from brass to a molded assembly cut weight while also producing savings on materials' costs. Previously, the valve was cast from brass and required multiple costly secondary machining to create complex flow paths.

The component is a dual tank water treatment control valve that provides a continuous supply of softened water from one tank while a second tank is being regenerated. The control valve regulates flow rates for resin regeneration, rinsing and flushing of the water softener. Measuring 5 x 3-3/4 x 5 inches, the valve services both resin tanks in the water softener.

The design challenge was to meet regulatory requirements for structural performance and water purity without sacrificing water flow rates.

"We began with a list of objectives developed with our customer that included meeting flow requirements, better appearing surface finish, weight and cost reduction, and faster turnaround time," says Ted Ahrenholtz, technical support manager with Minnesota Rubber and Plastics, Minneapolis, MN. "We worked together to design an assembly to replace the solid one-piece brass casting using computer-aided design (CAD), finite element analysis and stereo lithograph simulation (SLS)."

A three-part valve body configuration is achieved with the three components hot-plate welded together.

"We insured that rubber and plastic materials complemented each other's tolerance capabilities and that there was a careful balance between the torque value and contact of the seals," says Ahrenholtz. "We used thermoplastic injection molding on the three plastic valve body components and transfer molding on the NSF 61-compliant, chloramines-resistant rubber seals and O-rings. Through the use of finite element analysis, the wall thickness was optimized, conserving plastic material while increasing overall valve strength with less weight and reduced total cost."

Advantages of the new water control valve include a 7-percent weight reduction, a non-corrosive body, and identical inlet and outlet plumbing connections as on the brass valve. Use of lead was also eliminated.

Molding Replaces Cast Brass Valve
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