Results 1 to 13 of 13

Thread: using a flowmeter with a different gas

  1. #1
    Join Date
    Dec 2010
    Location
    Seattle
    Posts
    349
    Post Thanks / Like

    using a flowmeter with a different gas

    I have long wondered how a particular gas will flow through a flowmeter calibrated for a different gas. There are tables of correction factors given for some welding gases. But what if I'm concerned with a gas not shown in such tables?

    Here is a real world example. I have a Harris 355 flowmeter. Its glass tube has two scales. One is for CO2 and the other for argon. This flowmeter will attach to a helium cylinder. But there isn't a scale for helium, so how do I know how much helium is flowing?

    Victor gives a table of correction factors for various welding gases:

    argon.......0.85
    CO2.........0.81
    helium......2.69
    nitrogen...1.02

    If the argon scale reading is 20 cfh, to find the flow of helium through that flowmeter you multiply the argon flow by the ratio of correction factors.

    Example: argon flow = 20 cfh; helium flow = 20 * (2.69/0.85) = about 63 cfh.

    But where do the correction factors come from?

    It all starts with the periodic table of the elements, which gives the atomic weight for a single atom. Of course, gases don't always come as single atoms. What really matters isn't the atomic weight, it's the molecular weight.

    GAS....atomic weight....molecular weight
    Ar..........39.95.............39.95
    CO2.....C: 12.0 O: 16.....44
    He..........4.00...............4.00
    N2.......N: 14................28

    The molecular weight of air is generally accepted to be 29. Now we can calculate the specific gravity of each gas: specific gravity = MW / 29

    GAS........MW...SG
    argon.......40...1.38
    CO2.........44...1.52
    helium......4.0..0.14
    nitrogen...28...0.966

    The correction factor can be calculated from the specific gravity: CF = SQRT(1/SG)

    GAS........MW...SG.....CF
    argon.......40...1.38...0.85
    CO2.........44...1.52...0.81
    helium......4.0..0.14...2.69
    nitrogen...28...0.966..1.02

    Comparing, the calculated correction factors correlate exactly with the table from Victor.

    However, some welding gases are mixes, and the correction factor table from Victor doesn't contain gas mixes.

    A very common gas is 75% argon and 25% carbon dioxide (C25). What if we have a flowmeter calibrated for C25 and we want to know how to set it for hydrogen (for example - I wouldn't ever really want to)?

    The molecular weight of a known mix of gases is calculated from the molecular weights and percentages of the component gases.

    C25 molecular weight: .75 * 40 + .25 * 44 = 41
    C25 specific gravity: 41/29 = 1.414
    C25 correction factor: SQRT(1/1.414) = 0.84

    H2 molecular weight: 2 * 1.008 = 2.016
    H2 specific gravity: 2.016/29 = 0.070
    H2 correction factor: SQRT(1/.070) = 3.79

    So the amount of hydrogen that flows through a C25 flowmeter is 3.79/.84 or about 4.5 times the scale reading.

    Now I can calculate the flow of any known welding gas given the flow rate shown by a flowmeter calibrated for any other gas. Yay!

    Some flowmeters do not have regulators - they are intended to be connected to a regulator. Such flowmeters are only accurate if the regulator is set to the pressure that the flowmeter is calibrated for. But what if such a flowmeter is used with a different input pressure? How to correct the reading?

    Before I answer, a word about gas pressure. The pressure shown on the gauge is different from the absolute pressure. At standard temperature and pressure, to convert pressure shown on a gauge (psig) to absolute pressure (psia) you have to add 14.696 which is just atmospheric pressure.

    The formula to correct for pressure is (indicated flowrate) * SQRT((14.696+operating pressure)/(14.696+calibrated pressure))

    Example: a flowmeter calibrated at 50 psi is operated at 30 psi. How much is the flow reduced?
    The correction factor = SQRT((30+14.696)/(50+14.696)) = SQRT(44.696/64.696) = 0.831
    So the actual flow will be 83% of the scale reading.

    metalmagpie
    Last edited by metalmagpie; 11-26-2019 at 01:17 PM.

  2. #2
    Join Date
    Nov 2012
    Location
    new york city
    Posts
    6,987
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    too much math for me. i'd change the sight glass to one calibrated for helium and call it quits.
    i.u.o.e. # 15
    queens, ny and sunny fla

  3. #3
    Join Date
    Apr 2006
    Location
    Soda springs,Id
    Posts
    5,143
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Quote Originally Posted by docwelder View Post
    too much math for me. i'd change the sight glass to one calibrated for helium and call it quits.
    Same here!!
    Ol' Stonebreaker
    "Experience is the name everyone gives to their mistakes"
    Hobart G-213 portable
    Miller 175 mig
    Miller thunderbolt ac/dc stick
    Victor O/A setup
    Makita chop saw

  4. #4
    Join Date
    Feb 2015
    Posts
    578
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Great write up! I am lazy and just wing it based on how good my welds come out most of the time, i have made some marks with sharpies on some of my flowmeters based on calculations I have done in the past.
    ESAB Rebels 215/235, Hypertherm 85, 45xp, Miller 350p, Synchrowave 350 LX, Thermal Arc 185, Everlast 255EXT, TD 60i

  5. #5
    Join Date
    Jun 2012
    Location
    Laredo, Tx
    Posts
    5,095
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    As someone who has formal training/studies in mathematics and physics, I say bravo fortissimo.
    1st on WeldingWeb to have a scrolling sig!

    HTP Invertig 400
    HTP Invertig 221
    HTP ProPulse 300
    HTP ProPulse 200 x2
    HTP ProPulse 220MTS
    HTP Inverarc 200TLP
    HTP Microcut 875SC

  6. #6
    Join Date
    Jun 2012
    Location
    Laredo, Tx
    Posts
    5,095
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    metalmagpie, this is dedicated to your hard work digging up all that info. I have incorporated everything you have found into a Google Spreadsheet that anyone can use on their mobile cell phone if they have/download the Google Slides app. Once you have the app, you have to save a copy of this spreadsheet for yourself so you can edit the cells.

    It takes all the inputs from Steps 1-3 and finds the appropriate CF's and then does the math for you. Of course some Answers might be nonsensical due to the difficulty of trying to dial in super-low flowrates, but hey, I never said it would make it realistic in all situations!

    Here are screen shots:

    Flowrate & Gas Mix Calculator








    The 2nd tab is one that might be useful for those that don't have super expensive gas mixers and use Y's to tie together two tanks (it is for me, anyways). Enter your Desired flowrate for the specified gas mix, and it will spit out the actual individual flowrates:

    Gas Mix Calculator tab








    If anyone needs anything added to the Gas Mix tab for other weird gases, I can add them. Just ask.
    Last edited by Oscar; 12-22-2019 at 03:18 AM.
    1st on WeldingWeb to have a scrolling sig!

    HTP Invertig 400
    HTP Invertig 221
    HTP ProPulse 300
    HTP ProPulse 200 x2
    HTP ProPulse 220MTS
    HTP Inverarc 200TLP
    HTP Microcut 875SC

  7. #7
    Join Date
    Dec 2010
    Location
    Seattle
    Posts
    349
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Wow, Oscar, that's AMAZING!

    Only I'm never going to install any Google app. I value my privacy too much.

    Really Excellent Idea!

    metalmagpie

  8. #8
    Join Date
    Jun 2012
    Location
    Laredo, Tx
    Posts
    5,095
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Quote Originally Posted by metalmagpie View Post
    Wow, Oscar, that's AMAZING!

    Only I'm never going to install any Google app. I value my privacy too much.

    Really Excellent Idea!

    metalmagpie
    Oh well, lol. We use Google for work so I have to have it anyways. If I can incorporate it into a regular web page later on, I will. I just have to teach myself web design as that is not a thing a currently dabble in.

    Also, I can export my Google sheet an an Excel .xlxs and link it here for download. That would not require any app, but you would need Microsoft Excel on your computer or phone, or some other app/program that can open Excel .xlxs files.


    Flowrate & Gas Mix Calculator Excel File
    Last edited by Oscar; 12-25-2019 at 08:48 AM.
    1st on WeldingWeb to have a scrolling sig!

    HTP Invertig 400
    HTP Invertig 221
    HTP ProPulse 300
    HTP ProPulse 200 x2
    HTP ProPulse 220MTS
    HTP Inverarc 200TLP
    HTP Microcut 875SC

  9. #9
    Join Date
    Aug 2016
    Posts
    101
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Oscar:

    May I ask you to check your spreadsheet for C25 gas with Ar (@75%) and CO2 (25%)?

    I think it is calculating C25 at 67% Ar and 33% CO2.

    Thank you.
    Attached Images Attached Images  
    LINCOLN Power MIG 210 MP

    LINCOLN Ranger 330 MPX

    MILLER Thunderbolt AC/DC

    HYPERTHERM Powermax 190C

    HYPERTHERM Powermax 45XP

    HOUGAN HMD 505

    HOUGAN HMD 130

    FEIN/SLUGGER 14" COLD METAL CHOP SAW

  10. #10
    Join Date
    May 2017
    Location
    Pitman PA
    Posts
    476
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Dammit fellas...thats complicated stuff for a country boy.

    My hats off to you both for figurin all that out. Im glad I dont have to deal with that type of stuff in the work I do.

    That seems like a whole bunch of work there Oscar and Metalmagpie...all i can say is good luck with it...rather you than me

  11. Likes pinetree liked this post
  12. #11
    Join Date
    Jun 2012
    Location
    Laredo, Tx
    Posts
    5,095
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Quote Originally Posted by Ingenuity View Post
    Oscar:

    May I ask you to check your spreadsheet for C25 gas with Ar (@75%) and CO2 (25%)?

    I think it is calculating C25 at 67% Ar and 33% CO2.

    Thank you.
    Yup, you're right. Must have messed with it and not caught that glitch. Fixed now.
    1st on WeldingWeb to have a scrolling sig!

    HTP Invertig 400
    HTP Invertig 221
    HTP ProPulse 300
    HTP ProPulse 200 x2
    HTP ProPulse 220MTS
    HTP Inverarc 200TLP
    HTP Microcut 875SC

  13. Likes Ingenuity liked this post
  14. #12
    Join Date
    Aug 2016
    Posts
    101
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Quote Originally Posted by Oscar View Post
    Fixed now.
    Thanks, Oscar.
    LINCOLN Power MIG 210 MP

    LINCOLN Ranger 330 MPX

    MILLER Thunderbolt AC/DC

    HYPERTHERM Powermax 190C

    HYPERTHERM Powermax 45XP

    HOUGAN HMD 505

    HOUGAN HMD 130

    FEIN/SLUGGER 14" COLD METAL CHOP SAW

  15. #13
    Join Date
    Oct 2014
    Posts
    2,600
    Post Thanks / Like

    Re: using a flowmeter with a different gas

    Linde used to have square flow-meters with 4 different scales for different gases that could be rotated for the one you were using.

    http://www.bertolinoindustries.com/u...low-meter.html

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Page generated in 1,603,153,328.09409 seconds with 13 queries