| 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 the pressure within the drive cylinder is applied to both sides of 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, decreasing the driven cylinder pressure. The pressure reduction allows the sense piston to reset, restarting the process. The cyclic set and reset of the sense piston results in pressure oscillations within the conduit. The frequency of 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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