This is the complete steam valve for a La Marzocco GB5. It includes the steam valve body, steam wand ,steam knob and washers & fittings.

The steam valve in the GB5 has a brass body inside which runs a shaft. Turning the knob pushes the valve against the valve seat, allowing steam to pass into the body of the valve. The steam is prevented from passing along the sides of the shaft by a series of o-rings. All these steam valves have the additional protection of an anti-vacuum valve which prevents liquid being sucked into the steam boiler. It also prevents milk from remaining in the wand after use.