Re: Old dog learns new trick...Welding!
I'm not following this idea of "purging" the pressure from the machine after finished welding. There should be no reason to do that. The tank valve should always be shut off after using it but that is to prevent loss of gas in the event there is a leak downstream of the regulator. Any compressed gas cylinder, especially a flammable gas, should be valved off after use.
The flow meter/gauge will not be damaged by pressure left on it. The purge cycle I mentioned earlier is a position that when selected and the trigger on the handle is depressed, allows gas to flow through the tubing and tip without feeding wire or energizing the welder. This is to 'purge' air from the circuit prior to striking an arc. This is so the shielding gas will be there to envelope the arc immediately when you start welding. It doesn't need to be used every time you start just after the machine has set for a while. )think of it as turning on the hot water tap and letting it run until you get hot water) All welders don't have this feature, but they should. The alternative is to pull the trigger for a few seconds to get gas flowing but unless you disengage the wire feed mechanism you'll waste a lot of wire and the tip will be energized. Don't touch it.
Flow meters/guages are typically also pressure regulators. They reduce tank pressure that will be in the 2 to 2.5K psi (full tank) down to a usuable pressure. They have a constant pressure diaphram that once set, delivers a prescribed volume (cfh) of gas to the welder and out to the torch when the trigger is pressed via an electric solinoid valve which is built into the welder and activated by the trigger.
For still air conditions, no wind or inside where there is no draft across the weld area, the flow should be in the 20 to 30 CFH (cubic feet per Hour) range. Anthing higher than that and you're wasting gas. You can increase that flow if there is a slight breeze but a higher flow rate still will not help if there's too much air moving. That's where you need to shield the weld area from wind to keep the shielding gas from being blown away from the arc.
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