argon/CO gas pressure question/ help needed

The gas regulators for MIG welding have a small orfice and have the pressure at about 50 psi. If your regulator has a pressure gauge it may not be intended for use in MIG welding. But don't panic. You can make your own orfice and change the action from regulating pressure to regulating flow. But if you do this you need a way to know what the flow is. Google on " Binzel gas flow gauge ". I got a similar gauge sold or made by L-tec. Only cost about 5$.

Dan

Bruce, best bet is to buy a flow gauge, although one should have come with your

You buy a flow gage to replace your LP pressure gage and matching outlet fitting with orifice size specified on face of flow gage. Outlet fitting will also have CGA fitting needed to couple hose (another purchase) between welder and flowgage outlet fitting. Also need regulator inlet fitting or adapter so your regulator will fit CGA

If your regulator came with your welder, fits shielding gas bottle and fits hose to welder it is probably a flow gage regulator. In that case close look at fine print on gage indicating reduced pressure will probably show gage is calibrated in CFH. Flow gages respond to pressure changes but indicate flow rate through specified size orifice down stream.

The inexpensive "Flow meters" that come with the small machines are pressure based not flow. The second dial says CFM but is realy just a pressure reading. Mine will read 20 CFM even if no gas is flowing (as long as cylinder valve is open ). The better meters I have use a floating ball. No flow and the ball won't float. I once used a oxygen regulator with C25. It worked ok but I have since aquired many flow regulators. I suppose the regulator that came with my Lincoln weld pak reads ok for that machine but may be way off with another mig (each machine will have its own flow resistance.

The way those flowmeters work is they measure the drop in pressure across a calibrated orifice to determine flow. Just as Ohm's law relates voltage (pressure), current (flow), and resistance (restriction), the flowmeter rule works basically the same way. F=P/R where R is the constant restriction of the calibrated orifice. So flow is proportional to pressure, and the gauge face does the conversion from pressure to flow via its calibrated scale.

Now to get an accurate reading, gas has to be flowing, and the orifice has to be the primary restriction to flow. Since the orifice is very small compared to the other restrictions in a normal system, the latter condition is met. Just be sure that you only read the gauge when gas is flowing (ie when the trigger is pulled), and you'll get an accurate flow reading.

The ball in tube flowmeters work by a similar principle. The ball's position in the tube is a function of the gas pressure differential above and below the ball. The spring of the gauge is replaced by gravity (note that to read correctly a ball in tube flowmeter must be oriented pure vertical, orientation doesn't matter with the spring gauge type). The orifice is the difference in diameter of the ball and the tube.

Note that since the ball is usually pretty light, and gravity isn't as strong as the spring in a gauge type meter, the tube would have to be very long if it were constant diameter. So typically the tube is tapered. This lets much more gas flow for a given rise of the ball than a fixed orifice size would, and allows the tube to be conveniently short.

The combination of increasing pressure differential and increasing orifice size is included in the calculation to make the calibrated scale. So again, you just have to read it when gas is flowing, and you'll get an accurate reading.

The only real difference between the two systems is that with zero flow, the tube in ball reads zero, but the gauge type reads static pressure above atmospheric. When both are flowing freely, both read correctly.

Let me amend that slightly, since the ball in tube has to deal with varying gas velocity as well as a varying pressure differential, it will read differently for gases of different molecular weights (conservation of momentum law). So a ball in tube flowmeter may have multiple scales, one for each molecular weight gas it is calibrated to measure. The spring gauge type doesn't need this correction since its diaphram isn't in the direct line of flow, and will only have a single scale that'll be correct for all gases.

Gary

My flowgage has scale for Argon flow rates and different scale for CO2 flow rates.