Measuring Gas Flow Rate

What it is

Shielding gas flow is the volume of gas delivered per unit time. North American equipment usually reads in cubic feet per hour (CFH); metric equipment reads in liters per minute (L/min). The correct flow comes from the WPS or the equipment and wire maker. Too little lets air in; too much wastes gas and can cause turbulence that also pulls in air. AWS A5.32 covers the gases themselves, not the flow setting.

How to read it

• Flowmeter (tube with a ball float): read at the point the meter's maker specifies, most often the center of the ball. Hold the tube vertical. The scale is calibrated for a specific gas and inlet pressure.
• Flowgauge (pressure gauge with a fixed orifice): the dial shows flow based on pressure. It does not show a blockage downstream, so a kinked hose can read normal with no gas at the gun.
• Nozzle check: a handheld flowmeter placed over the gun nozzle shows what actually reaches the arc.

CFH to L/min conversion

1 CFH = 0.472 L/min. 1 L/min = 2.12 CFH.

Key points

• Use a flowmeter scaled for the gas in use. An argon-scaled meter reads wrong on helium and on many mixes.
• Argon/CO2 mixes are often read on an argon scale; check the meter's label.
• Drafts, fans and outdoor work increase the flow needed. Screens often work better than more gas.
• Larger nozzles need more flow; smaller nozzles need less.
• Check for leaks with a leak-detection solution. A leak can pull air into the gas stream.
• Set flow with gas flowing (trigger pulled or purge button), not with the valve closed.

Common mistakes

• Reading the top of the ball on a meter calibrated for center-of-ball.
• Using a flowgauge as proof gas is reaching the arc.
• Turning flow up to cure porosity caused by a leak or draft.
• Using a CO2 or argon meter on helium without a correction factor.

Governing standards: AWS A5.32; the WPS and equipment maker's instructions.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.