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Minnesota Rubber and Plastics

Water Control Valve Converted from Brass to Molded Assembly

Cost-Saving Redesign Reduces Material Usage and Energy Consumption

MINNEAPOLIS, Minn.--For one customer of Minnesota Rubber and Plastics, the redesign of a machined brass, water-control valve into a molded assembly, complete with threaded inserts, proved to be a cost-effective way to meet design goals while reducing material usage and energy consumption. Minnesota Rubber and Plastics made it happen by providing a molded valve with precise internal flow paths. The water control valve, a key component in the operation of an updated water softener design, had previously required costly secondary machining to create the complex flow paths.

The application involved 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 is critical to reliable water softener function by regulating 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.

For Minnesota Rubber and Plastics, the design challenge was to provide a molded water control valve equal to or better than the existing brass water control valve without sacrificing water flow rates; the company also had to meet regulatory requirements for structural performance and water purity. Price targets, material and energy savings, and just-in-time delivery were key requirements of the project.

"We met those design requirements, and more," reported Ted Ahrenholtz, technical support manager with Minnesota Rubber and Plastics. "We knew from the start that we would be able to reduce material usage, weight, and cost. Precision machined brass is expensive and heavy. Machining is slow, requires significant energy consumption, and there's a lot of residual scrap after machining.

"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," he continued. "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."

Minnesota Rubber and Plastics has a 50-plus year history of developing sealing solutions for complex applications. For this project, a three-part valve body configuration was developed; the three components were hot-plate welded together.

"Material design for this project was extremely important, not only for function and long operating life, but also to conserve material and energy needed to mold the components," said Ahrenholtz. "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. We used thermoplastic injection molding on the three plastic valve body components and transfer molding on the NSF 61-compliant, chloramine-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 75 percent weight reduction, non-corrosive reinforced thermoplastic body, and identical inlet and outlet plumbing connections as on the brass valve. Leak and pressure testing of each welded valve was also provided prior to shipping.

"By partnering with our customer in a co-designing effort, we were able to design, produce, and help our customer with a high-performance water valve that exceeded expectations using the latest design technology and our many years of sealing experience," Ahrenholtz added. "What's more, by eliminating the brass we eliminated the lead, so the new valve complies with government initiatives to reduce lead."