On espresso machines, there is some kind of pipe joint which allows the steam wand to move while maintaining its seal. What is this component called?
$\begingroup$ There may be different joints in use. Do you have a service or repair manual? Do you have a picture? $\endgroup$– martFeb 3, 2015 at 12:15
It is called a "steam wand gasket". Technically, it's a ball-and-socket joint made out of two concave PTFE (Teflon) gaskets and an EDPM gasket for the seal.
There may be other designs too; I learned this by watching Saeco StarBucks Barista - How to Replace Steam Wand Seals and Gasket (YouTube video).