Regulator and fittings: not quite a welding question but I hope you can help

[Robm]

Hi there. This is not a welding question but I think it is most likely to be answered by those versed in the welding art, hence my post here. I hope you can point me in the right direction.

I use compressed air for hobby work (driving model turbines) but my little 8 bar compressor has just sprung a leak so, since I'd like a little more than 8 bar anyway, I'm looking at buying air from BoC: their smallest (X) cylinder, 230 bar, looks about right. My question concerns what I need to connect to its [presumably standard] "5/8” BSP female right hand cone recessed" outlet.

I need to locate a regulator that will fit it, preferably one that offers both pressure and volume-remaining gauges and will give me up to 10 bar, maybe up to 15 bar, output. From the regulator I need to get to either a Series 21 pneumatic quick-connect type connector (like one of these) or a push-fitting for 4.5 mm/6 mm plastic tubing. Can anyone help me divine exactly what parts would suffice?

I know from experience that getting the exact right pneumatic fittings is not easy: all guidance gratefully accepted as I'm no expert in this, just need that air...

 

[AndersK]

You might want to look at a scuba tank instead of industrial grade air. Don't know the cost of filling scuba tanks in UK or if you have a dive center close but it used to be a lot cheaper than 17 £.

 

[Robm]

You might want to look at a scuba tank instead of industrial grade air. Don't know the cost of filling scuba tanks in UK or if you have a dive center close but it used to be a lot cheaper than 17 £.

Interesting idea: dive centres seem to be a bit thin on the ground around here but I will investigate further.

 

[Mr Fro]

I use 6mm plastic tube for all my welding gas - I just unscrew the original regulator fitting and pop a Festo push fit in there.

Do you need pressure and volume? You can calculate the volume given the pressure.

 

[Robm]

Just to be clear, is that 6 mm outside diameter plastic tube (so standard push-fit stuff)? When you say "unscrew the original regulator fitting", does that mean the regulators all come with the same size/thread fitting at some point in their output. Sorry if these are dumb questions but I'm feeling my way here.

On the pressure/volume thing I'd assumed it was easier to have both to hand/eye but if calculation does the trick it might reduce the cost.

 

[Mr Fro]

Just to be clear, is that 6 mm outside diameter plastic tube (so standard push-fit stuff)? When you say "unscrew the original regulator fitting", does that mean the regulators all come with the same size/thread fitting at some point in their output. Sorry if these are dumb questions but I'm feeling my way here.

On the pressure/volume thing I'd assumed it was easier to have both to hand/eye but if calculation does the trick it might reduce the cost.

Yeah, bog standard 6mm OD Festo (or equivalent) tube.

The outlet from all my regs are the same. I take those off and screw in a push fit (3/8" maybe - I'd have to check).

You can buy ready made adaptors which go from the standard reg outlet to a push fit but these are getting on for £40!

 

[Robm]

Great, so it looks like any old regulator will do the job.

Investigating BoC a little further they won't deliver to residential addresses and I seem to be equidistant, meaning 1 hour away, from all their collection points. I'll see if there's a more convenient option before I commit.

 

[Tangledfeet]

From the regulator I need to get to either a Series 21 pneumatic quick-connect type connector (like one of these) or a push-fitting for 4.5 mm/6 mm plastic tubing. Can anyone help me divine exactly what parts would suffice?

For genuine Parker Rectus 21 fittings (I use 6mm ID hose) I've bought from these guys on eBay:

Pardon our interruption...

(They did mistakenly send me a lesser alternative last week but was promptly sorted as soon as I pointed it out.)

 

[Robm]

Thanks: slightly cheaper than RS as well.

 

[Robm]

I've put a bid on a 12 litre diving cylinder to start me off, having verified that there's a place that will fill it up for me 10 miles away. Should at least get me started without making expensive mistakes.

 

[Cobbler]

I've put a bid on a 12 litre diving cylinder to start me off, having verified that there's a place that will fill it up for me 10 miles away. Should at least get me started without making expensive mistakes.

Make sure its in test, if it’s out, they won’t fill it.

 

[not done it yet]

Buy a 10Bar compressor?

 

[Munkul]

I don't mean to "down" your idea, but please bear in mind volume and air flow.

12 litres x 230 bar minus 10 bar =2640 litres of air total, before you have to refill, since you want it coming out at 10 bar.

Compare this to a cheap compressor

SGS 50 Litre Direct Drive Air Compressor - 9.6CFM, 2.5HP, 50L

This 50 litre air compressor is ideal for DIY and trade applications such as spray-painting, tyre inflation, nailing, stapling, sanding, drilling, cutting and grinding thanks to it's impressive 50L capacity and high flow 9.6 CFM air displacement.

www.sgs-engineering.com

50 CFM = 1415 litres per minute at 8 bar

So your dive bottle will last less than 2 minutes doing the same work as a proper compressor.

 

[cheb]

I can't remember the exact figure, but the first stage of a two stage diving regulator supplies air at about the same pressure as a good compressor. You can run windy tools from them, it's slightly safer than trying to use an electric drill underwater.

 

[Robm]

Thanks for the additional feedback. My other constraint is that this is being used in my loft workshop so noise is a large factor, hence the compressor I had which sprung the leak was a very quiet Jun-Air, which aren't so cheap (> £500); I was lucky to find the current one a few years ago at £150. The small BoC tank at 2.2 cubic metres would have been best but not being able to deliver makes that a real pain.

The scuba tank is in test but you're right that such a small run time is going to be painful. Nothing quite fits the bill, does it?

 

[Munkul]

I know what you mean... nothing gets on my nerves quite like the sound of a small direct drive compressor... my cheapskate uncle ran one for years for the motor vehicle workshop right in the middle of the place when the old, good one died... loud, underpowered, and full on annoying!

How abut trying to find a quiet screw compressor second-hand? Or just stumping up for the likes of a new shhh!air from machine mart? It will cost you less than dive bottle refills over a year or two... how much air do you need?

 

[Jim Davey]

Can the leak be trace then repaired?

 

[Kram]

Normal compressor, use it outside to fill a portable air reciever?

 

[Robm]

The leak is a pin-hole leak from the body of the compressor itself, which I guess is what I get for buying a used compressor that has opened and closed a door somewhere for many years. Seemed to me like repair might not be possible and, in any case, the compressor is somewhat under-powered for what I need so this is an opportunity to fix that.

I need two operating modes:
- main one is 10 bar for quite a short period, no more than a few minutes,
- secondary one is 5 to 8 bar over a 30ish minute period.

Recharging a cylinder with a noisy compressor outdoors is a very interesting option, only thing I will need to bear in mind is that I need to be able to lug the cylinder up two flights of stairs. And if you're wondering why I chose to put all the heavy stuff on the top floor of the house, yes, I know...

 

[Kram]

A smallish 25L air reciever wont be too bad without the compressor bits. Gas bottles are not fun to move either.
Another option is run a copper air line to the loft, which will benefit by cooling and removing water, and no air tank in the house.
If the old compressor tank is sound, you could use that. It is likely rated for 10 bar working pressure with much higher test pressure even if it only ran at 8 bar, but check it first with a bore camera in the inspecton hole.

I am interested to see the model turbines, any pictures?