| 摘要 |
A downhole mud pressure change signal generator has a signal valve to variably resist the flow of mud down the drill string bore. The valve is powered by a bias driver and controlled by a holding magnet that is in turn controlled by a downhole instrument. The bias driver has a spring opposed fluid powered piston that moves in response to changes in fluid pressure drop across the signal valve. The valve in normally biased closed. The bias driver is resiliently connected to the valve such that when the piston moves the bias driver in response to fluid pressure that overcomes the spring, the valve is urged toward an open position. When the valve is open and signal pressure across the valve is low the spring exerts more force than the piston and the driver urges the valve toward a closed position. The valve is urged to move but not compelled and is subject to latching in desired positions without losing the power needed to move later. The bias driver is used to power a latch that holds the valve open or closed. The energy is invested in springs that move the latch when holding magnets permit the latch to respond to the bias. The holding magnets never depend upon a flux gap because they hold positions the springs have provided.
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