Is this a silly question?

[the_big_1]

So I have got back in to mig welding, starting my kit car renovation.

Been using my old Clarke 90 with the Halfords disposable bottles (Cost me £11 as I have trade account)

And yes, started eating them now.

I start looking at new mig welders as mine is getting past it, metal size issues etc.

Looking at CWS welder when I spot the "Hobbyweld" gues link

£60 deposit for the bottle, £25.83 fill.

So first time, £85.83.

I read the spec and see "Capacity 1370 Ltr"

Now the Halfords disposable are "Volume: 950cc"

Now do I take that as 1370 ltr (1370000cc)??

That would mean 1370000cc / 950cc = 1442 disposable bottles for each refilable bottle????

 

[Crater Creator]

The SIP cylinders are supposed to be at 60 Bar pressure, so the gas volume is 60*0.95 litres = 57 litres.
So you'll get 24 times more actual gas in a Hobbyweld one (hobbyweld is what I use, as I don't do enough to justify a big bottle or a contract).

 

[the_big_1]

Hi ya,

So 60 Bar * 0.95 litre for a disposable = 57 litres.
137 bar * 1370 litres for refilable = 187690 litres.

187690 \ 57 = 3292 times bigger?

 

[MoreWellie]

you are mixing up bottle size and volume of gas inside

most of the larger hobby bottles are either 10 or 20 litre and when you factor in the 137 bar pressure the 10 litre hobby bottle contains 1370 litres of gas which is the equivalent to 24 small bottles

 

[the_big_1]

BOC for 2L

230 Bar * 494 litre = 113620 liters.

113620 \ 57 = 1993 times bigger?

 

[MoreWellie]

nooo where dd you get the 494 from?

a 2 litre bottle at 230 bar contains 460 litres of gas

even as a hobby welder I found the 2litre boc bottles too small and needed about a refill per month

 

[the_big_1]

The hobby site doesnt say what the bottle sizes are, just pressur. Only the ultra size at 20l but I guess the standard is 20l to but less pressure?

Hobby

60 Bar x 0.95 litre for a disposable = 57 litres.
137 bar x 20 litres = 2740 litres.

= 48 times more?

BOC

60 Bar x 0.95 litre for a disposable = 57 litres.
230 x 2 liter = 460 litre

= 8 times more?

 

[the_big_1]

lol i got it at the same time you guys put it lol

 

[the_big_1]

So for a cost point,

1 x Hobby (20L) £60 deposit, + £25.88 fill = £85.88 (Only first fill)

If I was buying the equivelent disposable, that would cost 48 x £11 = £528 lol

 

[chunkolini]

I started doing the maths years ago when I got my first Mig welder.
I realised that there were so many noughts involved that disposables made no sense whatsoever.

 

[the_big_1]

If its 10L

1 x Hobby (10L) £60 deposit, + £25.88 fill = £85.88 (Only first fill)

If I was buying the equivelent disposable, that would cost 24 x £11 = £262 lol

So the Hobby bottle at first fill save £176.12

After that, each fill is saving £236.12

 

[Chris Stevens]

If its 10L

1 x Hobby (10L) £60 deposit, + £25.88 fill = £85.88 (Only first fill)

If I was buying the equivelent disposable, that would cost 24 x £11 = £262 lol

So the Hobby bottle at first fill save £176.12

After that, each fill is saving £236.12

If you are likely to use any more than about 4-5 hobby cylinders a year, I think you might find a contact and size W is likely to be less money? Maybe not so if you are paying full retail price for gas refill's, but not sure very many people actually pay those prices?

 

[rtbcomp]

If you're talking about liquid CO2 then you can't multiply the volume by the pressure to get the volume at 1 atmosphere. That only applies to compressed gas, such as CO2/Ar mix.

You've got to use mass as the basis for your calculations.

 

[Chris Stevens]

There are so many questions about gas on here, that I wonder whether it would be worth working out the actual cost of the more common gases, in relation to the various deals available currently? I get the feeling that bearing in mind the high cost of refills, hobby gas is probably more costly as soon as usage goes over a certain level?

 

[addjunkie]

The two main gas equations you require for true comparision are.

P1xv1/t1=p2xv2/t2 and pv=nRT

P is pressure, t is temprature, v is volume, all in base units. n number of moles of gas, R specific gas constant of the gas, T temprature difference in kelvin.

 

[MoreWellie]

For home use I find the 10litre bottles big enough to last a reasonable period and light enough to move around easily (when it isn't on the trolley)

It is easy to get caught up in how much money each size saves and look to save the most

BTW your 10l and 20l examples show the same prices for deposit and refill. I presume this is wrong