When to purge the line...

[ZINOM]

Hi All,

I have a simple mig unit (Lincoln Weld-pak 100) and was told to close the tank and bleed off the gas from the system when I was done using it.

My question is when does this need to be done?....if I'm welding in the morning or noontime, can I leave it as is until I shut down the workshop late at night?....I may not be using it the next day, but sometimes I don't know if or when I'll go back to use it the day that I AM using it...know what I mean?

I want to do what's best for the machine, but I'd rather not be purging, then remembering I needed to do some more welding...then purging....then...


Thanks for the help,

John

[Willy]

Probably not gospel but this what I've always done for the last forty years. No problems yet.
If I am going to not use the machine for an hour or two I just close the gas valve(s).
If I'm done for the day I close the valve, release the pressure from the regulator and hose, and I back off the regulator adjustment screw so as to leave it parked in a relaxed condition.
This is what I was taught and it has served me well, as sometimes I may not get back to it for a week or more.
I use this procedure for both my oxy-acetylene and mig cylinders.

[1911man]

Zinom, listen to your uncle Willy, I was taught the same way. The little bit of gas you lose in purging don't amount to a hill of beans and it's easier on your equipment. Also makes you pay more attention to your settings.:)

[radkins]

Count me in for the same advice, I too have been doing it that way for about 40 years and see no reason to change.

[Bill736]

I think there's more to be said about this subject. There's a good reason to purge acetylene from gauges and hoses. Acetylene is a potentially unstable gas , outside of the stabilizing matrix inside the gas cylinder, and should be purged for safety reasons. However, CO2 , argon, and oxygen will not spontaneously explode, so I'm not sure why purging is necessary. Perhaps it extends the life of the regulators. Any other opinions ? ( Edit added later- that's true, just venting the line is not actually a purge. I'm speaking of just venting the pressure.)

[Mcostello]

I've heard it doesn't allow the seat to deform when held under pressure.

[Highpower]

Perhaps it extends the life of the regulators.
That's what I was taught. Haven't had a single problem with a regulator yet (30 years), so I guess it's working..... :D

[radkins]

I don't actually "purge" the line just close the tank, release the regulator and bleed the hose. Actual "purging" would involve flushing out the hose with air or another gas which would be totally unnecessary with a MIG and there would be no practical reason to do so with Oxygen or Acetylene.

[Highpower]

I've heard it doesn't allow the seat to deform when held under pressure.Which is why I close the tank, bleed the hose (and regulator), then release the adjustment screw on the regulator. However I do purge my MIG hose with the bottled gas to remove any air before I start welding again, just to make sure I'm getting shielding gas at that first arc instead of plain atmosphere. :)

[radkins]

However I do purge my MIG hose with the bottled gas to remove any air before I start welding again, just to make sure I'm getting shielding gas at that first arc instead of plain atmosphere. :)


That, of course, should be standard procedure anytime the pressure is bled from the hose! Usually makes for interesting starts if it's not done. :)

[ZINOM]

You guys are awesome....thanks for all the replies and information!

John

[ligito]

The one time I forgot to release the pressure on my Oxy-Acetylene valves, I ended up having the regulators rebuilt because of damage to the diaphragms.

[ZINOM]

So if I back off on the adjustment screw on the regulator....do I re-set it the next time in a similar fashion to the way I set my oxy/acetylene?

Do I open the bottle, start the machine and squeeze the trigger (with the drive rollers disengaged) to start the flow of gas...and then turn the screw in to the desired pressure?

I know it might sound dumb, but I just want to make sure I'm thinking about it correctly....and I'd rather ask now than later.

Thanks All,

John

[radkins]

Sounds like you have a pressure regulator instead of a flow meter so you need to determine the setting you need first. Recommendations of this or that pressure setting from someone usually will only put you in the ballpark and you really should set what works best for your welder. Start with a piece of scrap and start welding on that while at the same time slowly turning down the gas flow until you just start getting porosity in the weld, you will be able to tell when the gas flow gets too low. When this happens slowly turn the gas back up until the weld becomes smooth and clean again then add a couple of PSI and remember that setting so you can put it back every time you turn the gas on. Too little gas will destroy your weld and too much gas, while it will not hurt the weld in the least, will hurt your wallet! If, just for instance, you are using 30 PSI on the gauge and 20 PSI would work just as well you would be wasting a third of your gas! These numbers are just examples and are not suggested settings so try yours to see what works for you and you may find you can save a lot of your $hielding gas. The reason a pressure setting that works for one welder may or may not be right for another is that you are not really concerned with gas pressure (PSI) but rather gas flow (CFH). Because of various differences in equipment, such as diffusers and fittings, a given pressure for one welder may deliver a very different amount of flow (CFH) on another machine so you need to adjust yours to your needs.