| 摘要 |
A dual-head flow controller having a positive-head and a negative-head for supplying a sample fluid from a source to a restriction at a constant rate, with the magnitude of the negative head about the same as that of the positive head, independent of the pressure of the source fluid. A positive-head tube having a distal open end connects for fluid communication with the supply. The positive-head tube extends a first predetermined distance above a mean elevation of the restriction in the measuring chamber. A negative-head tube communicates fluid from the restriction to a distal open end. A portion of the negative-head tube extends downwardly a second distance below the mean elevation of the restriction. The fluid, being communicated in response to the combined head pressures, flows at a constant rate through the restriction, independent of changes in the pressure of the source fluid.
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