  We study quantitatively the formation and radiation acceleration of
electron-positron pair plasmoids produced by photon-photon collisions near
Galactic black holes (GBHs). The terminal ejecta velocity is found to be
completely determined by the total disk luminosity, proton loading factor and
disk size, with no dependence on the initial velocity. We discuss potential
applications to the recently discovered Galactic superluminal sources GRS1915,
GROJ1655 and possibly other GBHs.
