The standard centrifuge method based on Alder et al. (1997).
Vulnerability curves are generated to measure how hydraulic conductivity declines at increasing levels of drought and xylem tension (http://biologylabs.utah.edu/sperry/methods.html#vulnerability_curves). The centrifuge method has been developed in John Sperry's laboratory at the University of Utah. It has been successfully modified by Li et al. (2008).
We recently confirmed that the standard centrifuge method can accurately measure the loss in hydraulic conductivity in long-vesselled olive branches; see Hacke et al. (2014) for details.