Aluminum Workshop: Two flowmeters don’t make a right

I’m sure that we have all seen people engaging in poor practices in many fields from time to time. Today I want to discuss one poor practice that I commonly see and to urge all of you not to do it.

When you are setting up your welding equipment, never lead the shielding gas through more than one flowmeter. Leading the shielding gas through two (or more, which is even worse) flowmeters on its path from the inert gas cylinder or the central source from where large installations supply shielding gas will almost always cause problems.

Typically, a shielding gas source, such as a high-pressure gas cylinder, needs a pressure regulator to reduce the gas pressure in the bottle (usually 3,000 PSI for a full bottle) to a level that can be used for welding (between 20 and 50 PSI). A pressure regulator is screwed onto the gas bottle. It is common to combine the pressure regulator with a flowmeter. You have all seen them. They are the clear plastic tube a few inches long that have an adjustment on them to set the shielding gas flow rate.

The problem arises when you attach the gas hose from the flowmeter to your wire feeder because many feeders already contain a flowmeter. This is intended to be a convenience, allowing you to set the shielding gas flow rate at the feeder without going all the way back to the gas bottle. Because of this, you’ll always set both flowmeters for what you think is a reasonable flow rate—for example, 40 SCFH.

Now you have a problem.

Although both flowmeters read 40 SCFH, your actual gas flow rate is almost always much less because you are using two flowmeters in series.

What should you do? The best thing is to bypass or eliminate one of the flowmeters. Instead of using a regulator/flowmeter on the bottle, use just a regulator and set the flow rate using the flowmeter on your feeder. Or try to bypass the flowmeter on the feeder and use the regulator/flowmeter at the gas bottle to set the flow.

If you can’t do this and you must use the two flowmeters in series, set the flowmeter at the bottle wide open to the highest flow rate possible and use the flowmeter at the feeder to set the actual flow rate. This isn’t the best solution, but it is better than doing nothing.

Last, I recommend that you have one of those simple and inexpensive gauges that you can place over the end of the gas nozzle on your torch that measures gas flow. Most welding distributors have them readily available. They are pretty accurate and can tell you whether you have the gas flow you think you have, whether you have the problem above, whether you have a leak in your gas hose, or whatever else.