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any way to convert psi to cfm?

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  • any way to convert psi to cfm?

    hello everyone I picked up a lincoln sp 135 at a garage sale good shape but no regulator.
    my uncle gave me a regulator cga 580 connection but the low side is in psi not cfm, is there a way to convert psi to cfm?

  • #2
    PSI is a measure of pressure and CFM is a measure of flow rate. Although the flow is related to pressure, there is no simple and universal relationship between the two that would allow you to transform a pressure into a flow. You have to determine how the pressure effects flow for your particular set up. Assuming that everything else stays the same, doubling the pressure will approximately double the flow.

    Simple way to measure the flow is fill a quart jug with water and invert it in a bowl. Then stick the hose into the bottle and count how many second it takes to fill the jug. Filling a quart jug in 15 seconds is 1 gallon per minute.


    • #3
      You CAN convert, if there is a calibrated orifice through which the gas will flow, BUT...

      While 10-20 CFH (not CFM) is the recommended flow, you don't really need to KNOW the number. You just need the shielding.

      Hook it up, and turn it all the way down until you get porosity. Then nudge it up until you don't get any, and leave it there. Let us know what that number is for future reference.


      • #4
        Just get one of these, $6.43.
        What do I know I am just an electronics technician.


        • #5
          For $39.95, the HTP Flowmeter #12020-F will give you an accurate flow measurement.

          The HTP Flowmeter is almost identical in appearance to the Victor 0781-2731 shown above.
          Barry Milton

          HTP Invertig 201
          HTP MIG2400

          Trailblazer 302, Spoolmatic 30A, Suitcase 12RC
          Clarke Hotshot


          • #6
            Yes You Can But Don't!!

            Having made literally thousands of tests of pressure versus flow when inventing our patented Gas Saver System a quick answer is it will take about 3 to 8 psi in the gas hose to flow 30 to 35 CFH! However, it will vary while welding as the small gas hose in the MIG gun cable is bent, as spatter builds in the gun nozzle and for other flow restriction reasons! That is why all proper regulator/flowmeters or regulator/flowgaugues (those with 2 gauges, one calibrated in CFH) operate above 25 psi. It is called choked flow. The needle valve or very small orifice (typically 0.025 inches in diameter) in a regulator/flowgauge operates above 25 psi to achieve what is called “automatic flow compensation.” The folks developing MIG and TIG in the 1950's knew about these flow variations and used this approach. It relies on the fact that gas flow in a small hole or needle valve cannot exceed the speed of sound. That is why you see lightening before you hear the thunder!
            Use the proper regulator/flowmeter or regulator/flowgauge. If you want to improve, your weld starts and reduce gas waste and surge, see for a detailed explanation. Unlike low-pressure devices some have tried (such as the Harris Gas Guard) to reduce starting surge and found they vary gas flow 30% or more, our simple inexpensive Gas Saver System maintains “automatic flow compensation.” It also supplies a controlled amount of shielding gas at weld starts to purge air from the weld start area. Sorry for the long answer!
            Last edited by Jerry U; 07-23-2014, 08:51 AM.