Gas Pressure

   / Gas Pressure #1  

bindian

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After having a Mig welder for about 5 years, I finally bought a tank of 75/25 gas and a roll of unshielded wire. I figured my Hobart manual would tell me the pressure, but nothing is there. What pressure do I dial in to send to the torch? Do I just crack the bottle open, like acy., or open it all the way?
hugs, Brandi
 
   / Gas Pressure #2  
Typically Hobart MIG run at 20CFH (Cubic Feet a Hour)... Surprised you could not find that tidbit of data, its in my Manual for my HH140....

Some say you can go as low as 10 and other as high as 30, but the recommended 20CFH seems to work fine for me....
20cfm.jpg


Also if you are a Hobart owner...

 
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   / Gas Pressure #3  
Brandi, Dale is correct but he answered a different question - you should SLOWLY crack the tank valve til you start seeing pressure come up on the high pressure gauge - once it's up, open the valve all the way. The OTHER gauge (if there is one, instead of a rotometer) is your flow rate - I too set mine at 20 CFH. BTW, that IS a pressure gauge too, but it measures the pressure DROP across an orifice in order to show FLOW rate. Some regulator sets use a rotometer (bb in a tube) to measure flow, either one is fine.

Another change from what you're used to - weather's gettin' warmer, but if you try to weld with 75/25 and have a FAN blowing on you to keep cooler, you will NOT like the welds - you're into animals, pick your favorite excrement and your welds will look worse - Same thing when (not IF) you forget to turn on the gas before you weld - anybody here who claims they've NEVER done that is almost guaranteed to be LYING :devilish:

Have fun... Steve
 
   / Gas Pressure #4  
I typically run around 15 in the shop ... which is an enclosed area not prone to breezes.
 
   / Gas Pressure
  • Thread Starter
#5  
Typically Hobart MIG run at 20CFH (Cubic Feet a Hour)... Surprised you could not find that tidbit of data, its in my Manual for my HH140....

Some say you can go as low as 10 and other as high as 30, but the recommended 20CFH seems to work fine for me....View attachment 703004

Also if you are a Hobart owner...

I saw that, but I was looking for a pressure setting.
hugs, Brandi
 
   / Gas Pressure
  • Thread Starter
#6  
Brandi, Dale is correct but he answered a different question - you should SLOWLY crack the tank valve til you start seeing pressure come up on the high pressure gauge - once it's up, open the valve all the way. The OTHER gauge (if there is one, instead of a rotometer) is your flow rate - I too set mine at 20 CFH. BTW, that IS a pressure gauge too, but it measures the pressure DROP across an orifice in order to show FLOW rate. Some regulator sets use a rotometer (bb in a tube) to measure flow, either one is fine.

Another change from what you're used to - weather's gettin' warmer, but if you try to weld with 75/25 and have a FAN blowing on you to keep cooler, you will NOT like the welds - you're into animals, pick your favorite excrement and your welds will look worse - Same thing when (not IF) you forget to turn on the gas before you weld - anybody here who claims they've NEVER done that is almost guaranteed to be LYING :devilish:

Have fun... Steve
So set it at 20psi........Right? I build a fan under my welding table. It blows up and between my legs. Hope that works out good.
hugs, Brandi
 
   / Gas Pressure #8  
Dale, you and I are NOT arguing, I merely added an explanaton of HOW the gauge on the left accomplishes a FLOW indication - "I too set mine at 20 CFH. BTW, that IS a pressure gauge too, but it measures the pressure DROP across an orifice in order to show FLOW rate. Some regulator sets use a rotometer (bb in a tube) to measure flow, either one is fine."

Proof - if I'm wrong, then the "flow" gauge would drop to ZERO when you release the trigger on the MIG gun, right? Try it; once you've released the trigger, the "flow" gauge will actually INCREASE its reading slightly - does NOT usually mean there's a leak...

Brandi, please re-read my earlier post - yes, that gauge (on the left in Dale's picture) reads PRESSURE, 'cause it's a pressure gauge - but it MEASURES the FLOW rate (ONLY when the mig gun is actually WELDING - the gauge on the RIGHT only reads TANK pressure (once you SLOWLY open the tank valve ALL THE WAY)

If either of you needs more info to understand how this works, please ask; my entire career was spent in tech fields, the last 33 years in heavy industrial instrumentation and control, so NOT some "internet expert"... Steve
 
   / Gas Pressure #9  
Dale, you and I are NOT arguing, I merely added an explanaton of HOW the gauge on the left accomplishes a FLOW indication - "I too set mine at 20 CFH. BTW, that IS a pressure gauge too, but it measures the pressure DROP across an orifice in order to show FLOW rate. Some regulator sets use a rotometer (bb in a tube) to measure flow, either one is fine."

Proof - if I'm wrong, then the "flow" gauge would drop to ZERO when you release the trigger on the MIG gun, right? Try it; once you've released the trigger, the "flow" gauge will actually INCREASE its reading slightly - does NOT usually mean there's a leak...

Brandi, please re-read my earlier post - yes, that gauge (on the left in Dale's picture) reads PRESSURE, 'cause it's a pressure gauge - but it MEASURES the FLOW rate (ONLY when the mig gun is actually WELDING - the gauge on the RIGHT only reads TANK pressure (once you SLOWLY open the tank valve ALL THE WAY)

If either of you needs more info to understand how this works, please ask; my entire career was spent in tech fields, the last 33 years in heavy industrial instrumentation and control, so NOT some "internet expert"... Steve
I'm sorry my comment was not intended for you, I am in total agreement with you in principal.... THE comment with graphic was intended for Brandi who insists on using the incorrect term of PSI, Yes, you and I both know the Burdon tube type gauge reads pressure and is calibrated through a orifice and DISPLAYED AS CFH.... So CFH is proper terminology...

Sorry if I ruffled your feathers, it was not my intention at all to disagree with you....
 
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   / Gas Pressure #10  
No prob Dale; I've worked with too many "manly men" who thought us Instrument "prima donnas" were afraid to get their hands dirty for my skin to be that thin -

last 10 years or so I was lead man of a 11 man rotating maintenance crew consisting of millwrights, pipe fitters, welders, machinists, electricians, and me - when I started talking about retiring they offered to take up a collection to get me to STAY - not only were they surprised at the things I knew something about, they also liked that I tended to tell the company to F off if they tried to get my crew to tackle a job that wasn't safe... Steve
 
 
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