A loop heat pipe (LHP) is a heat transfer device that uses the vaporization of a working fluid to transfer heat from an evaporation section to a condensing section. The operating characteristics of a LHP with a two-way pressure regulating valve (PRV) is experimentally investigated using a flight-qualified LHP. Experiments suggest that an orifice within the PRV causes a premature start-up. It is determined that the LHP is unable to control the evaporator temperature to 31 ℃ roughly after 130 W under test conditions. The LHP is found to be more sensitive to changes in sink temperatures when operating at higher powers. A steady-state LHP model is developed and was found to compare well with experimental results. It is determined that modeling the effects of the PRV on the LHP operation is not feasible using measurements due to the extreme sensitivity of the model to small changes in fluid pressure.