| 摘要 |
A pin is formed with an axial bore at the bottom end for receiving compressed air and containing a diffuser. This bored end has a portion of progressively increasing cross section toward the end. A pair of axially spaced diametrical openings in space quadrature intersect the axial bore. A bumper with a resilient face may be urged toward the pin when an air switch is open. A source of compressed air is coupled to the pneumatic cylinder through an air switch and to sample and reference conduits through a pressure regulator. There are needle valves between the pressure regulator and the sample and reference conduits, respectively. A meter measures the differential air pressure between the sample and reference conduits.
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