Universal Microsystems
High precision, restrictive flow orifices for
gas flow control

Phone: 408-727-1313 E-mail Us

1/4" VCR Re-Useable
Gasket Flow Restrictor

Note: Helium does permeate PCTFE at a low rate


Find the orifice ID for the application

You will need:
  • Q the application's flow in sccm
         standard conditions are 14.70 psia and 20oC)
  • Pi the inlet pressure in psia (atmosphere + psig)
  • K a constant for gases other than nitrogen
       =(28.0/MWgas))1/2 or see table
  • Po the outlet pressure in psia (if known)
  • Then calculate (Q/Pi) x (34.7/K)
        the nitrogen flow at 20 psig from the desired orifice
  • Look up the orifice ID from best match in Flow Table.

    Note: If Po > Pi /2 substitute Q/[Po(Pi -Po)]1/2 for (Q/Pi)and 17.35/K for 34.70/K.  
    Also, multiply Q by (Tgas/293)1/2 with T in Kelvins,
    if the temperature of the application gas differs significantly from 20oC.


  •          Flow Table

    Note: Helium does permeate PCTFE at a low rate
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    Universal Microsystems