Abstract: A method and apparatus to attenuate a flapper valve from oscillating is presented. An inertia tube is added to the flow path of the flapper valve nozzle, which effectively produces a stabilizing pressure force on the flapper at its natural frequency. The inertia tube has a length to area ratio of greater than approximately 1000 in/in2. The addition of an inertia tube to the nozzle makes the fixed size orifice of the nozzle behave like an orifice having a size that is a function of flow frequency. The inertia tube may be a straight tube, a coiled tube, a thread passage and the like.

Abstract: A variable displacement pump fuel metering system wherein an electrohydraulic servo-valve powers a pump actuator to control pump displacement and variably bypasses fuel as an integrally related function to improve flow dynamics. The electrohydraulic servo-valve withdraws fuel from the pump output flow to drive the pump actuator and thereby control the displacement of the pump. The amount of bypassed is inversely proportional to the amount of fuel used to drive the actuator so that metered flow is maintained when an increase in pump output is demanded. The variable displacement pump may also meter flow in the downstream manifold. The electrohydraulic servo-valve is electrically controlled in a closed loop circuit with a flow sensing valve providing the feedback to an electronic engine controller. The electronic controller directly controls the electrohydraulic servo-valve.

Abstract: A fail-safe second stage valve for controlling actuator movement upon power loss in a multiplexed fluid power control system. The second stage valve is interposed between a corresponding actuator and a fluid multiplexer to operate generally as integrating or amplifying device which regulates flow to the actuator. The second stage valve is provided with a dampening mechanism in the form of a bleed port to reduce fluid flow to the actuator. The bleed port bleeds off accumulated fluid received by the second stage valve over a predetermined range of valve positions. This changes the position of the valve and thereby reduces flow rate to the actuator. The multiplexed fluid power control system using the fail-safe second stage valve controls the flow to the corresponding actuator upon electrical power loss. The actuator may be used to open and close variable stator vanes in an aircraft gas turbine engine.

Abstract: A differential pressure regulator connected in a fluid system including a bypass line and including a valve body with a high pressure inlet and a compensation inlet connected to the high pressure side of the system, a low pressure inlet, and a bypass outlet. A valve member is reciprocable within the valve housing and includes an intermediate passage between the compensation inlet and the bypass outlet, a metering port between the intermediate passage and the bypass outlet, and a compensating port between the compensating inlet and the intermediate passage. The position of this valve member controls the degree of opening of the ports. Also included is spring biasing the valve toward the closed position of the ports. The high and low pressure inlets are coupled to high and low pressure faces on the valve member, and the resulting forces act with the spring force to adjust bypass flow to achieve the substantially constant pressure drop.

Abstract: A multiplexed hydraulic control system in which high force margins for the multiplexer are achieved by employing hydraulic oscillators as the multiplexer driving means. The multiplexer is typically in the form of a hydraulic cylinder having an input port and a plurality of output ports, with an operator in the cylinder for individually connecting the input port to the output ports. The hydraulic oscillator is mechanically coupled to the multiplexer operator, and oscillation of the former causes oscillation of the latter to sequentially connect the input to each of the outputs. Various means are taught for initiating reversal of the oscillator and controlling the oscillation speed.

Abstract: Apparatus for controlling the flow rate of fuel fed to a gas turbine engine, particularly but not exclusively to prevent overspeeding of the engine above a maximum safe level in the event of failure of a primary control system and associated components. A first control valve V3 is associated with means for sensing pressure drop .DELTA.P across a series metering valve V1 and arranged to control the opening or closing of a bypass valve V2 to keep .DELTA.P essentially constant and equal to a set point. A second control valve V4 is associated with a speed-sensing governor and arranged to control the opening or closing of that same bypass valve V2, so that engine fuel rate is controlled to maintain speed at an overspeed set point if abnormal conditions or failures tend to cause overspeeding.