Flow Control Devices (FCDs) have demonstrated significant potential for improving recovery in Steam Assisted Gravity Drainage (SAGD) production wells. One initial hypothesis was that steam breakthrough was delayed because the FCDs better homogenized injection and production by equalizing flow and compensating for pressure changes along the wellbore. However, in many cases, the field results were far greater than such an approach would have justified. The actual physics for this process are unclear, and not demonstrated in literature. Upon review of field data published by ConocoPhillips, the possibility of a steam blocking effect was proposed (Stalder, 2012), although the physical basis for this effect was not explored. This paper proposes an updated hypothesis to explain this effect, presents preliminary data to support the assumption, and introduces a new apparatus and methodology to characterize FCDs for SAGD applications. The traditional approach to steam control states that steam flashing at the producer should be avoided, as it will eventually lead to a completion failure. Alternatively, the proposed hypothesis contemplates using steam flashing at the producer to regulate flow in various segments of the completion, thus better enforcing conformance. The physics of this process will primarily be described analytically; however, this effect was also observed qualitatively in a small-scale experiment where water was flashed across an orifice. In order to design SAGD completions that leverage FCDs (and this effect), it was necessary to accurately characterize different FCDs under these challenging multiphase flow conditions. Since vendors use a variety of approaches when designing their FCDs, a protocol was developed to create a characterization procedure which was independent of the underlying FCD design and architecture, resulting in a direct comparison of the overall performance of each FCD. Part of this protocol required the construction of a new, high temperature multiphase flow loop capable of subjecting FCDs to representative SAGD operating conditions. Through fine control of the relevant test parameters, accurate performance measurements can be obtained for each FCD. This paper will present some information regarding the design and specifications of this new flow loop, as well as impart some of the lessons learned from its commissioning and initial operation.