What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
Preflow and postflow control when shielding gas reaches the TIG torch. Preflow sends gas before the arc starts; postflow keeps gas flowing after it stops. Set them too short and the tungsten or weld can oxidize. Set them much too long and you waste gas without improving the weld.
The right settings depend on the torch, cup, gas flow, material, and how you start and stop. Use the welder’s manual and your gas supplier’s guidance where available, then adjust from practical starting points below.
What preflow and postflow do
Preflow purges air from the torch and establishes a shielding-gas envelope before the arc forms. It matters most with a gas lens, a large cup, long torch leads, or a start that needs a moment to stabilize. Too little preflow can leave the first part of the weld contaminated; too much mostly adds delay and uses gas.
Postflow protects the hot tungsten and weld pool as they cool. If shielding ends while either is still hot, the tungsten can turn dark or the weld can discolor or oxidize. Postflow is especially important on stainless steel, aluminum, and other materials that show contamination readily. A dusty or drafty workspace can also disrupt shielding even when the timer is set correctly.
Starting settings for common work
These are practical starting points, not universal specifications. Many welders offer preflow in seconds and postflow either in seconds or through an automatic setting based on amperage.
| Work or setup | Preflow starting point | Postflow starting point | What to watch for |
|---|---|---|---|
| Short welds on mild steel, standard cup | 0.2–0.5 seconds | 4–6 seconds | Increase preflow if the start is porous or visibly contaminated. |
| Stainless steel, short welds | 0.3–0.7 seconds | 5–8 seconds | Keep shielding over the crater and hot tungsten. |
| Aluminum or higher-amperage work | 0.3–0.8 seconds | 8–12 seconds | Use longer postflow as current and tungsten temperature rise. |
| Large cup, gas lens, or long lead | 0.5–1 second | As required by material and amperage | A larger gas volume may take longer to establish; avoid excessive flow that causes turbulence. |
For a useful first setup, try 0.5 seconds of preflow and 5 seconds of postflow on light steel work. For aluminum or higher amperage, begin nearer 8 seconds of postflow and inspect the tungsten after each stop. If the welder has automatic postflow, check its manual to see whether it adjusts with amperage and what its minimum and maximum times are.
How to set and test the timers
Find the preflow and postflow controls in the welder’s menu or on its front panel. Confirm the units: a setting of “5” might mean five seconds, but controls vary. Set the gas flow at the regulator or flowmeter as well. For many TIG setups, roughly 15–20 cubic feet per hour (CFH) is a reasonable starting range with a standard cup; a gas lens or larger cup may need more. Follow the torch and cup guidance, and don’t compensate for drafts by turning flow up excessively—turbulence can pull air into the shielding envelope.
Make a few short test welds on clean scrap using the same cup, gas flow, and approximate amperage you plan to use. Watch the start and stop, then check the weld and tungsten. A porous or dirty start points to a shielding problem: check preflow, gas supply, hose leaks, cup condition, and drafts. A discolored tungsten after the arc stops suggests inadequate postflow or a torch moved away too soon. Keep the torch over the end of the weld while postflow runs.
Change one setting at a time. Add preflow in small steps, such as 0.2 seconds, if starts remain contaminated after checking the gas system. Add postflow by a second or two if the tungsten still oxidizes. If the tungsten looks clean and welds are sound, longer timers offer little benefit. A foot-pedal operator should also maintain torch position after releasing the pedal; the welder cannot shield a hot tungsten if the cup is pulled away.
Common mistakes and what they cost
Too little postflow can contaminate tungsten, making it harder to restart cleanly and sometimes requiring a regrind. Too little preflow can cause defects at the beginning of a bead, where they may be easy to miss. At the other extreme, long timers slow repeated tack welds and consume extra gas. If a 1-second preflow works reliably on your setup, there is no reason to use 3 seconds by default.
Also check for leaks before increasing timer settings. A loose fitting or damaged torch hose can waste gas continuously, and no timer adjustment fixes a leak. Use the correct gas for the process, keep the cup free of spatter, and protect the work from fans or open doors. For a basic TIG setup, a suitable TIG gas flowmeter makes it easier to set and repeat flow than guessing from regulator pressure alone.
Choosing a welder with useful controls
For occasional repair work, a welder with simple, adjustable preflow and postflow is usually enough. Paying more for automatic postflow or fine timer increments can be worthwhile if you make many short welds or switch often between low- and high-amperage work. Before buying, check whether the machine specifies timer ranges and whether gas timing is adjustable in both TIG modes you intend to use. A machine that lets you set postflow precisely is more useful than one with a vague “gas” control.
If you are building a TIG setup, prioritize a dependable torch, consumables, and a regulator or flowmeter appropriate to your gas before buying accessories aimed at saving tiny amounts of gas. A gas lens kit can improve shielding on some joints and make a longer postflow practical, but it does not replace correct flow, clean parts, or protection from drafts.