The part above is from a typical household espresso maker. The purpose of the valve stem is to allow steam to be diverted to the milk steamer and to prevent the passage of hot water and steam unless a filter basket is attached.

The original part was molded out of plastic. While in the closed position the valve is pushed by a cam against a seal. A return spring pushes the valve up. After a short period of use the spring seat sheared off of the valve stem body.

Space considerations did not make it possible to thicken the spring seat. A replacement part was manufactured from stainless steel. While a stainless steel part is slightly more expensive to manufacture changing the valve stem makes the coffee maker more reliable leading to a lower number of customer complaints. The new valve stem also has marketing potential: "Stainless Steel Valve" will sell more coffee makers than "All injection molded parts."

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