Rancilio Complete One Group Expansion Valve Assembly
These are only used in the Epoca, Promac and Laranzato one group models. They function as both a check valve as well as an expansion valve. The expansion valve is the portion that exhausts out to the drain. They now come with a barbed fitting instead of a threaded fitting that connected to a rigid copper drain pipe. You may need to purchase a length of silicone hose to retro-fit your equipment to use this new version valve: the old rigid pipes are out of production (however...).