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Purge molbloc - clean contamination from molbloc

If you believe that your laminar molbloc is contaminated (showing more flow than is actually going through it) you might purge it to try and clean it. Bellow are instructions to do this.

  • Purging should only be done if you are OK with changing the calibration of the molbloc. Purging may significantly change the output of your molbloc. If you have doubts, check with your quality team and/or send to Fluke Calibration for evaluation.
  • Purging is performed in nitrogen only
  • Purging is not recommended for liquid contamination, return for authorized service
  • Take "As Found" data for all calibrated gases prior to a purge
  • The molbloc is removed from the flow path circuit and connected to a N2 gas supply to the molbloc’s outlet connection so that flow will be against the normal flow direction and the inlet connection is venting to atmosphere.
  • If an attempt to capture the contamination is to be made, a clean white towel is placed over the upstream molbloc connection.
  • For molbloc-L elements range 1E3-L and above (or any molbloc SN 470 and below) the N2 supply regulator is set to 100 psig.
  • For lower range molbloc-L elements the N2 supply regulator can be set from 100 - 200 psig.
  • For most molbloc elements flow will be audible at these pressures.
  • The purge can continue up to 10 minutes, but it is most likely that the contamination is purged within the first 10 seconds
  • Comparing “As Found” data to data after the purge is the easiest way to judge if contamination was purged from the molbloc. Comparing the pre- and post-purge runs, the most common sign of contamination being removed would be a downward shift in the slope of the molbloc from the pre-purge linearity. The purge should be repeated as necessary to ensure as much contamination as possible has been removed.

See the article, Filter on molbloc inlet flange, prevent contamination, for information on how to add a filter to the inlet of your molbloc to hopefully prevent contamination. 

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