Flow Control and Test Orifices

 
             Lenox Laser has the ability to drill and flow calibrate small holes. These holes can be as small as 0.5 microns and as large as several thousand microns in diameter. The holes are flow calibrated by comparing them to hundreds of standards. The standards have been certified by the flow engineering staff at Lenox Laser using a certified absolute pressure gauge and other accurate, proprietary methods. When an orifice is flow calibrated, a hole with a flow diameter is established. This diameter is close to the actual diameter whether the hole be square, or any other shape with sharp or rounded edged. This flow diameter can be used to predict the flow of any gas or gas mixture under a fixed set of conditions by using simple mathematical formulas. The gas equations are established for clean, dry air which we use for our testing. Also, note the list of different units of pressure.
              Temperatures and pressures must be absolute when doing gas flow calculations. The inlet pressure used in our basic equation is 29.7 PSIA. This is factored in as the constant ‘C’. Altitude and changes in barometric pressure influence accuracy when using pressure gauges that reference local pressures. These gauges can be used if corrections are made for the altitude provided a good barometer is available and frequent adjustments are made. Otherwise, use a pressure gauge that gives pressures in absolute pressures for accurate results.

             The equations incorporate changes in the molecular weight to accommodate gases or mixtures of gases other than air. Factor#3 (see chart) is used when ∆P/P1 is less than 0.48 which results in a subsonic flow rate. The gas equations are as follows:                                                  

(P1 and P2 must be absolute pressures with each different pressure designation)

• A corresponding constant ‘C’ must be used as follows:

• PSIA- C = 5.889(10^-4)

• Pascals- C = 8.5413(10^-8)

• KPA – C = .85413(10^-4)

• TORR – C = .1139(10^-4)

• BAR – C = .00854

• Kg/M² - C = .8375(10^-6)

• Inches Hg – C = 2.884(10^-4)

• Flow = cubic centimeters per minute

• ΔP = P1- P2 in pressure units designated

• d1 = flow diameter in micro-meters

• M.W. = molecular weight of gas or mixture

• Factor #3 = a factor used to calculate gas flow when ΔP/ P1 is less than 0.5

As with gas flow, liquid flow can be through calibrated orifices. Take note, that a liquid is not compressible therefore different formula are required for calculations.                                 

• Flow = cubic Centimeter per minute

• d2 = flow diameter in micro-meters

• ΔP = P1- P2 in pounds per Inch²

• ρ = density relative to water

           Lenox Laser has been drilling and flow calibrating small holes for over fifteen years. In this period of time, many types of metals, glass, plastics, and customer specific materials have been drilled and flow calibrated. Our flow calibrated orifices are very accurate and can be used in most quality testing procedures. One of the widespread applications of our flow calibrated orifices is in the semiconductor field where gases are metered into gas boxes for growing computer chip crystals. A multitude of uses exist for our orifices. If you have any questions or need any technical assistance call:
Lenox Laser at (800) 49 HOLES or (410)592-3106 and; e-mail quotes@lenoxlaser.com.

Lenox Laser Flow Factor #3 Values Chart