Improvements in or relating to gas turbine engines

781,430. Gas turbine plant. RUSTON & HORNSBY, Ltd. April 25, 1955 [April 24, 1954], No. 11886/54. Class 110 (3). A gas turbine plant in which powdered fuel is fed to a combustion chamber by fluidization which occurs in two stages comprising a fluidizing column working at atmospheric pressure which feeds fuel to a second fluidizing column working at a pressure appropriate to the combustion chamber pressure has the fuel supply to the atmospheric fluidizing column controlled by a device having a piston sliding in a cylinder, the setting of the piston being controlled by a diaphragm which is responsive to the static pressure difference between the dilute phase and the bottom of the bed in the atmospheric column. The dilute phase is stated to be the space above a fluidized bed in which there are solids entrained in the upflowing gas. The invention is described with reference to the gas turbine plant described in Specification 781,427. The static pressures referred to are connected to unions 56 on opposite sides of a diaphragm chamber. The diaphragm 58 controls the buildup of pressure in a cylinder 59 and hence the setting of the piston 60. The piston 60 is connected to adjustable blades which control the rate of delivery of fuel to the atmospheric columns. Specifications 781,428, 781,429 and 781,431 also are referred to.