GB789670A - Improvements relating to hydraulic speed responsive circuits - Google Patents

Abstract

789,670. Axial-flow compressors; gas-turbine plant. ROLLS-ROYCE, Ltd. Oct. 13, 1955 [Oct. 13, 1954], No. 29562/54. Classes 110 (1) and 110 (3). [Also in Group XXIX] In an hydraulic speed-responsive system comprising a positive displacement fixed capacity pump driven by a prime mover and producing in the pump delivery line a pressure drop across a variable restricted orifice which is a function of the prime mover speed and causes a pressureresponsive means to effect a controlling action associated with the operation of the prime mover, there is provided on the downstream side of the orifice, inflow and outflow connections through which an external source of liquid enters and leaves the system and through which the flow is regulated to maintain the pressure at the pump inlet in excess of ambient atmospheric pressure. As shown, a gear pump 10 driven by a gas-turbine engine produces a pressure drop across a variable orifice 12 restricted by a valve 13 supported by a capsule 14 which is housed in a chamber 15 connected to a temperature bulb 16 sensing temperature at the compressor inlet so that the opening of the valve is in accordance with a preselected value of engine speed divided by the square root of compressor inlet temperature. Ducts 11b, 17b connect the upstream and downstream sides of the orifice respectively to opposite sides of a diaphragm 40 carrying a valve 41 which in association with a fixed restriction 48 in a branch 22a of a line 22 supplying liquid to the system from an external high-pressure source to keep the pressure at the pump inlet above atmospheric and the system liquid cool, controls the leak-off from the branch 22a into a line 17a connected to a deaerator 18. The amount of leak-off controls the pressure acting on the larger side of a servomotor piston 44 against full pressure acting on its smaller side. The piston 44 which through its rod 45 may adjust either the inlet guide or stator blades of an axial-flow compressor or the bleed valves therefor moves to load a spring 46 to an extent proportional to the adjustment of the blades or bleed valves. The valve 41 will open when a preselected value of pressure drop across the orifice 12 is reached and this value depends upon the position of the piston 44 due to the rate of the spring 46 so that for each speed of the engine over a certain range there will be a corresponding position of the piston 44. Liquid passing into the system through the line 22 passes through tangential flow-restricting orifices 24 in a sleeve 25 of the de-aerator 18 to produce a swirl and thence through radial bores 28 to a pump supply line 19, any free air or vapour in the liquid forming an axial core and passing through an orifice 27 in a partition 26 in the sleeve. Liquid after passing through the orifice 12 passes into the line 17a and together with any leak-off through the valve 41 enters the de-aerator through elongated tangential slots 30 and then passes into the pump supply line 19. Under the conditions when the valve 41 is passing liquid the amount of liquid in the system may be in excess of that required by the pump 10, any excess liquid together with the free air or vapour is then expelled through a pressure-relief valve 20. The relief valve 20 may, if desired, be replaced by a flow restrictor. The external supply source of liquid may be from the high-pressure fuel supply system, any excess liquid expelled through the valve 20 being returned to the inlet side of the main fuel pump. On the omission of the spring 46 the system could maintain a constant speed of the engine, the piston 44 being connected to a fuel control. Specifications 704,849 and 713,436 are referred to.