Orifice Sizing Information
 

As the holes become larger  the flow tolerance becomes smaller. 

Flow calibrating an orifice establishes a flow diameter which can be used to accurately calculate the flow rate of any gas or mixture of gases at any set of know conditions.

The measured diameter of holes do not account for the shape of the hole and its leading edges which effect the flow rate.  There are many equations and methods to calculate flow but none are more accurate than our method of flow calibration using our online calculator or our flow diameter equation. 
 

Important requirements for accurate flow:

1.  Flow through the orifice must be in the same direction as it was calibrated.  (High pressure side is marked on VCR® gaskets with a dot)

2.  Orifices must be tightly sealed in the flow system as leaks can vary results.

3.  Pressures in the flow system, must be controlled and maintained constantly.

4.  Temperature must be controlled and maintained to the designed conditions.

5.  The flow conduit must be free of any constrictions and be at least four times larger in diameter than the orifice. 

Sample Flow Rates For Gases Through Small
Holes @ 29.7 P.S.I.A to Atmosphere

***Lenox Laser defines a one Micron hole will pass 0.01749sccm of dry air per minute with an inlet pressure of 29.7psia and an outlet pressure of 14.7psia regardless of the hole shape, actual diameter, approach velocity, and other variables. All other flow rates are proportional in accordance with the laws of gases. 

Caution:

14.7psia / atmosphere @ sea level 
15 psig = 29.7psia  @ sea level. At higher elevations adjust the gage pressure to 29.7psia