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What gas preflow and postflow do
On a TIG welder, preflow releases shielding gas before the arc starts; postflow keeps gas flowing after it stops. Preflow helps clear air from the torch cup before the tungsten and workpiece become hot. Postflow shields the hot tungsten and weld as they cool. Too little coverage can cause oxidation, a dirty tungsten, or a discolored weld. Too much mostly wastes gas.
Adjustable timing is useful when you change torch cup size, electrode diameter, amperage, or the demands of the material. It is not a substitute for correct gas flow, clean metal, or sound torch technique. For many routine jobs, a machine with fixed but sensible gas timing is adequate. If you regularly weld stainless, work at higher amperage, or need to tune shielding for repeatable results, separate preflow and postflow controls are worth looking for.
How to choose a TIG welder with flow adjustment
Check the manual or front-panel specifications for independently adjustable gas preflow and postflow. Some welders offer postflow adjustment but use fixed preflow; others provide a configurable gas sequence through menus rather than dedicated knobs. “Gas solenoid” alone does not mean either timing is adjustable.
For DC TIG on mild steel and stainless, prioritize stable low-amp control, a usable duty cycle, and the right input power. Aluminum requires AC TIG. If you need both, an AC/DC machine is generally the practical choice, but costs more and may have a lower duty cycle on a given circuit. Match the welder’s maximum draw to your outlet and breaker; a machine advertised for high output may need 240 V to deliver it.
Use the table as a buying checklist, not as a claim that every machine in a category has the same controls. Verify the exact version before purchase, since features can vary by model and regional configuration.
Compare the main options
| Welder type | Gas timing to look for | Best fit | Main trade-off |
|---|---|---|---|
| DC TIG inverter | Independent adjustable preflow and postflow, if available | Steel, stainless, repair work | Does not weld aluminum with TIG |
| AC/DC TIG inverter | Separate timing controls, ideally with a clear adjustment range | Aluminum plus steel and stainless | Higher price; confirm input power and duty cycle |
| Entry-level TIG welder | Check whether preflow is fixed and postflow adjustable | Occasional hobby work and basic repairs | Fewer tuning options; may be fine for short, simple welds |
If you are shopping for steel or stainless, compare DC TIG welders with adjustable preflow and postflow. For aluminum as well, look at AC/DC TIG welders with adjustable gas timing. Treat those as search links, then verify the manual for the specific machine rather than relying on a generic listing description.
Practical starting settings
Start with the manufacturer’s recommended settings and adjust from there. A preflow around 0.2–0.5 seconds is a reasonable starting range for many manual TIG setups; small cups and short starts may need less, while larger cups or a longer torch lead can need more. A postflow starting point of roughly 1 second per 10 amps is a commonly used rule of thumb, not a universal requirement. For example, at 100 amps, try about 10 seconds, then inspect the tungsten and weld before changing it.
Gas flow is usually set at the regulator or flowmeter, not by the preflow control. Many gas-lens or standard-cup setups start around 15–25 cubic feet per hour, but cup size, drafts, and torch arrangement matter. More flow is not always better: excessive flow can create turbulence that pulls air into the shielding envelope. Keep the torch close, avoid drafts, and check for leaks if the flow setting seems unusually high.
Recognize the common failure modes
If the arc starts with a contaminated tungsten, the weld turns gray or sooty, or the tip degrades quickly, check preflow, gas flow, leaks, and shielding before blaming the welder. A short preflow can leave air in the cup at ignition. If the tungsten turns blue or black just after the arc stops, postflow may be too short, the torch may be moving away too soon, or gas coverage may be disrupted. Increase postflow in small steps—one or two seconds at a time—and compare results.
Long postflow is not automatically safer. It consumes shielding gas and slows the next start if the sequence requires waiting. A small cup in a sheltered shop may need less coverage than a large cup on a hot, exposed weld. For repeated production work, record settings that produce clean starts and bright tungsten rather than relying on a rule of thumb alone.
A short buying checklist
Before ordering, confirm whether both timings are adjustable independently, whether the display is in seconds, and whether the machine stores settings between power cycles. Check torch and pedal compatibility, included consumables, input voltage, and the duty-cycle rating at the amperage you expect to use. For occasional low-amperage steel work, a less expensive DC machine with a fixed preflow can be a sensible buy if its postflow and arc performance are adequate. Pay extra for AC/DC or more timing control only when the jobs you actually do call for it.