| 摘要 |
In a measuring while drilling or similar system, a pressure balance drive cylinder exhaust valve is driven by a toggling sense piston. Reset of the sense piston creates a pressure balance across the exhaust valve such that, as the pressure within the drive cylinder regeneratively increases, this pressure is applied to both sides of the exhaust valve. The pressure balance thus created greatly reduces the force necessary to close the exhaust valve. Once the sense piston is driven past the toggle allowing the drive cylinder pressure to have an offset pressure equal to the downstream main valve pressure, the drive cylinder forces the exhaust valve open thus decreasing the drive cylinder pressure. The pressure reduction allows the sense piston to reset, thereby restarting the process. Because the main poppet is driven by the drive cylinder pressure, the cyclic set and reset of the sense piston results in drive cylinder pressures that alternatively insert and remove the poppet from the orifice causing pressure oscillations within the conduit. The frequency of this oscillation is controlled either by the rate that fluid is allowed to enter the drive cylinder or by a sear used to interrupt operation of the sense piston.
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