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MG Midget and Sprite Technical - Welding gas bottles

I am using commercial type bottles for MIG gas. An Argon / C02 mix in a 10 litre bottle supplying through a proper regulator. The last 10 litres seemed to go very quickly an I am wondering if maybe I had a leak on the system although I do check the connections with soapy water each time. I also always turn off at the bottle rather than the regulator between uses to minimise the risk anyway.

As I am about to connect up a new bottle I thought I would ask advice here. Should I use any sort of sealing paste on the dome of the brass connection to the bottle? I never have done in the past. I just check the surfaces are clean and undamaged but maybe that isn't sufficient?

GuyW

You shouldn't need any form of sealant as those fittings are designed to seal without any. If the surface of the dome or female cone is damaged resulting in a leak then either the dome fitting should be changed or if the bottle seat it returned for exchange.
David Billington

Exactly what David said :-) With the possible caveat that it is always possible that the cylinder's pillar valve is not sealing fully. In which case the cylinder should be exchanged.
Greybeard

OK, Thanks both. That is as I thought. No sealing paste. Actually, although this isn't a welding gas I have an idea that sealing paste on a gas bottle is definitely a no-no! Something about potential explosions?

This time I will check all the connections with soapy water, which I think I forgot to do last time. Its quite possible it didn't leak away - I did do quite a lot of welding on the back end of the Frilly Frog.
GuyW

Guy, I too have a 10 litre Argon/CO2 mix, (SGS gas, Somerset, rent-free) still on the first bottle. It started at 200 bar and is now at 120 so I presume just over half left, if pressure translates to volume. Did yours drop quick!Y from around 100 bar or gradually? It may be the gas valve in the welder is leaking?
W Bretherton

I don't know about your particular bottle/valve Guy, but some gas bottle are meant to be used with the valve fully open to the stop to prevent leakage.

Charley
C R Huff

Also check the gas flow , i use a gas flow gague thats attached to the gauges on the bottle
Kevin Stevens

The gauges l have show bottle pressure and gas flow in litres / Min. I usually weld at around 7 unless it is outside when l may turn it up to 10 or so.l am using the same bottles as you, Bill, from SGS. I was previously using a 20l bottle which lasted well over a year. I swapped that for the 10l size, not sure when, but this side of Christmas.
The flow rate is controlled by the knob on the valve set, so that is never fully open. It screws down to regulate to my chosen a flow rate. As far as l can tell the knob on the gas bottle itself just opens or shuts the supply. Is that the one you think needs to be opened up fully Charlie?

GuyW

I've cringed in the past when I've seen people use PTFE sealant tape on gas bottles, propane wouldn't likely be an issue but I've seen it used on oxygen bottles and that is the danger as you can get oxygen safe PTFE tape and apparently some may contain oil which would be a serious problem and 230bar oxygen likely behaves differently to that out of the regulator at say 1 bar.

Regarding MIG torches you can get flow gauges which fit over the MIG shroud for a quick test as not all regulators have horizontal outlets for the flow gauges to fit onto, my MIG regulator doesn't, my TIG regulator does.

I did once have a BOC oxygen bottle with a defective valve where it was difficult to open and then I couldn't close it fully so I took it straight back and they swapped it immediately free of charge.
David Billington

Guy
Just a thought
When you do the soapy water check, it might pay to give the handpiece a spray as well--The shut off valve in the machine itself could be weeping and letting gas escape out the handpiece between uses while it's all turned on
willy
William Revit

Willy, that is a good suggestion, and could very well be the problem! At around about the time of the last 10l bottle l had treated myself to a new torch unit as the old one had seen it's day! The replacement one came pre assembled with the gas pipe feed tube and control cable. I cannot now remember checking inside the handle and it's possible, though careless of me, that l just connected up at the MIG welder! Tut tut!
GuyW

Guy,

I don't know enough about the valves to tell anything from your photo. It is just a vague warning that I remember from years ago. Your supplier should be able to tell you. I think on my oxy/acet set, the ox is to be opened fully and the acetylene didn't matter.

Charley
C R Huff

Ive found i the past ....skmetimes when you get a good day, the welder is humming and the beads are tight...its easy to loose 3 hours and lunch without a 2nd thought.


Last week i went thur 5- 1pound bags of spaghetti..
I couldnt belive it, and dug thur the trash... 5 empty wrappers... i guess i had a hidden hunger for spagetti

Prop
1 Paper

Guy, I have some gas leak detection foam which I originally purchased for checking the gas fire connection etc. It would readily detect leaks on the welder gas feed. I ought to check mine although it seems to be lasting well.
W Bretherton

I am not alltogether sure there is a leak. It may just be that l did a lot of welding! Soapy water will usually detect a leak but l was originally just asking about good practice and if there was a paste l should have been using. Now l have a fresh bottle l will be more methodical with soapy water checks when l first connect it up.
GuyW

Guy,

It may be worth getting a flow gauge set-up as in my experience single stage regulators increase their output pressure as the input pressure decreases so periodic checking of the gas flow rate might be worthwhile to get the most usage for your £s. This sort of thing may be handy if you can't fit one on the regulator http://www.ebay.co.uk/itm/New-Argon-Co2-Gas-Flow-Meter-Tester-Flowmeter-For-Mig-Welder-Tig-Welder-/152117800504 .
David Billington

Thanks David. Is that what mine is then - a single stage regulator ? (as shown in photo)
GuyW

Guy,

Yes that looks like a single stage regulator, 2 stage regulators are larger and maybe 4" diameter, at least those I have experience with, and I have only ever seen them for oxygen and acetylene IIRC. They have the benefit of maintaining near constant outlet pressure over long periods irrespective of the bottle pressure. I can only guess that they're not provided for shielding gas use as it doesn't make much difference if the gas flow is out from optimal although in some cases too high a flow can cause issues as can to little. Too little flow can lead to poor shielding and too much flow can cause turbulence which entrains air and lead to poor shielding at least in TIG welding, maybe MIG as well. With non perfect gases such as propane where it's in liquid form until the bottle is nearly empty you have a fairly constant bottle pressure so a single stage is all that is required.
David Billington

Thanks, that makes sense.
The other aspect is that MIG gas is pretty cheap really, (£32 for my 10L @ 200bar ) so at least for DIY use the actual flow isn't hugely cost critical. Unless of course one is experiencing either of the flow rate faults that you describe.
GuyW

Guy,

I'll have to check that cost against my BOC rentals for Argoshield for MIG and I have argon as well for TIG, I think for the amount I do maybe BOC works but will check. I think this year I'm giving up the BOC oxygen bottle rental as I am currently using an ex medical oxygen concentrator and using oxy propane instead of oxy acetylene, OP is not quite the same as OA but for what I do it works well and the oxygen concentrator pulls O2 out of the ambient environment as required so no pressurised O2 cylinder. The one I have fits my needs and 2nd hand costs about the same as the yearly bottle rental and a cylinder fill so pretty much a no brainer to make the change.
David Billington

David, I don't know about other gasses, but for my type of use for Argon/CO2, and my (normally low) consumption, then SGS is far more economical than BOC. I used to have a BOC account, but for my low level use I was paying far more just in annual rental than the for gas I was using. The SGS source is gas only and Zero rental on the bottles.
GuyW

Boc do a hobby account under a vw deal ,im using it st the moment

,http://www.mig-welding.co.uk/forum/threads/boc-and-volkszone-gas-offer.14605/
Kevin Stevens

This thread was discussed between 10/04/2017 and 12/04/2017

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