A solenoid valve moves an armature back and forth between valve open and
valve closed positions without the armature having any sliding engagement
with any fixed valve part. This is accomplished by supporting the
armature with a spring having one periphery engaging a fixed valve
surface and another periphery engaging the armature so that armature
movement causes flexure of the spring, but no sliding contact. This helps
prevent generation of dirt within the valve and ensures accurate armature
movement to make the valve durable and reliable. Springs in both washer
and cylindrical helical shapes can accomplish this.