8.5 Apertures

Theo Wilson -

Apertures may be used to control the sample flow, split flow or make-up flow. Putting and aperture in a flow path will set the flow to a constant value as long as the pressure is constant.

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 Outer view and cross-section of push-in orifice, showing flow restriction

  • The apertures used with the At-Line Sampling Module are 2.5 mm press-in orifices in stainless steel from Lee Co.
  • Different sizes of aperture are available, which will restrict the flow by different amounts.
  • During method development, controlling the flow rates with a mass flow controller or rotameter may be more convenient, as this allows for greater flexibility. Once a method has been defined, however, using apertures to control the flows gives good repeatability.
  • To control the sample flow, an orifice should be inserted into the particulate filter block, as shown in the At-Line Sampling Module Manual.
  • To control the split or make-up flow, the orifice should first be pushed into an equal length of 1/8” PTFE tubing and then inserted fully into the relevant port.
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