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.