Patent GB-763602-A (GB)
IPC: F02C9/28
Abstract: 763,602. Gas turbine jet propulsion plant; axial How compressors. ROLLS-ROYCE, Ltd. Aug. 9, 1954 [Aug. 28, 1953], No. 23901/53. Classes 110 (1) and 110 (3). [Also in Group XXIX] A gas turbine engine comprising a highpressure compressor driven by a high-pressure turbine and a low-pressure turbine driving a low-pressure compressor and directly or through reduction gearing a propeller has a bleed valve through which air compressed in the low-pressure compressor is vented to atmosphere to avoid surging of the compressor and means adapted to open the bleed valve at reduced rotational speed of the high-pressure compressor relative to the rotational speed of the low-pressure compressor. A low-pressure compressor 1 driven by a low-pressure turbine discharges into a high-pressure compressor 2 driven by a highpressure turbine. The compressor 2 discharges into combustion equipment which supplies working fluid to the high- and low-pressure turbines. A propeller is connected to the lowpressure compressor through reduction gearing. Centrifugal pumps 10, 11 driven through gearing from the high- and low-pressure shafts respectively draw fuel from the pipe 37 and discharge it through ducts 12, 13 to chambers 14a, 14b on opposite sides of a flexible diaphragm 14. Tappings 15, 16 may be taken to governor devices 40 forming part of the fuel supply to the engine combustion equipment to prevent overspeeding of the rotors. The diaphragm 14 loads one end of a pivoted lever 17 through a push rod 14c so that on increase of the discharge pressure of the pump 10 relative to that of the pump 11, the half-ball valve 18 is lifted. The lever 17 is also loaded in the sense of opening the valve 18 by a spring 20 mounted between abutments 21, 21a. The abutment 21 is carried by bellows 22 responsive to the ambient air temperature or engine intake temperature as measured by a temperature-sensitive element 26. A threaded portion 23 allows the position of the bellows 22 to be adjusted manually. The outer wall 27 of a duct between the low- and high-pressure compressors has ports 28a through which air may pass to atmosphere through ports 28 controlled by valves 29. The valves 29 are controlled by a piston 31 arranged in a cylinder 32 loaded on one side by a spring 33 and on the other by fluid under pressure supplied through a pipe 35 containing a restriction 36. The arrangement is such that under normal operating conditions the ports 28 are closed. When the speed of the low-pressure rotor exceeds a predetermined ratio of the speed of the highpressure rotor the half-ball valve 18 is lifted. Fluid then passes through the bleed pipe 19 and the pressure in the chamber 34 falls which allows the spring 33 to move the piston 31 and open the ports 28. The temperature-sensitive element 26 varies the loading on the spring to vary the ratio of the rotor speeds at which the valve 18 is lifted. The predetermined ratio of the speeds of the two rotors is determined by suitably selecting the gear ratios between the rotor shafts and the pumps 10, 11. In a modification, the control of the bleed valves 29 is of the follow-up type and a special device is provided to obtain a speed signal.