The L-valve, as a solids flow control device, has been used extensively in fluidized beds and circulating, fluidized beds for controlling the solids circulation rate. Knowledge on L-valves, however, is Mostly limited to ambient flow conditions with Geldart A and B particles. Studies on the L-valve under high temperature conditions which are common in industrial applications are rare. This paper describes experimental studies that probe the characteristics of the L-valve operation under high temperature conditions using Geldart D particles. The relationships between the solids flow rate, aeration rate, and pressure drop are investigated and compared With those under ambient conditions using different groups of particles. The results indicate that the variation of the solids flow rate controlled by the L-valve aeration depends on the actual internal flow rate of the gas that flows through the L-valve rather than the external aeration flow rate of the gas that is introduced into the system. The actual aeration gas flow rate required for generating a given solids flow rate is the same so long as the location of the aeration tap is above the height-to-diameter ratio of 1.5 in the L-valve. Operating the L-valve with Geldart D particles needs more gas aeration compared to that with Geldart A and B particles for a given solids flow rate. However, under high temperature Conditions, the solids flow for Geldart D particles in the L-valve behaves like those with Much smaller particle sizes. For Geldart D particles, the aeration gag flow rate required under high temperature conditions is much less than that under ambient conditions.