Reducing to lower pressures 3

[carheight]

Ok you clever lot, I’ve finally found you and now you have to (have to, have to, have to, have to) answer my tricky question, which is (interesting background story first):

2 of my favourites hobbies are diving and building model aircraft (not at the same time).
For diving I use a 15L cylinder at 230 Bar.
For model aircraft (painting of) I use a friends’ noisy compressor for powering my airbrush at a constant 2 bar.

Now, ingenuous that I am, I thought “lets bypass the compressor (and painful parting of £150, roughly €210 for our funny little European friends) and feed the airbrush from my diving cylinder”.

What I am after is a valve that I can attach to my diving cylinder (it will probably actually be bigger tank and a lesser pressure, say 40-50L at 8-10 bar) that will reduce higher pressure to the lower 2 bar I need to operate my airbrush. I clearly would need the valve to maintain a constant (2 bar) exit pressure, regardless of the internal higher pressure which will decrease over time as I use the air.

Does such a vale exist, and if so where can I get one. Any idea of price too.

Thanks (a lot) in advance, Daniel.

 

[quark]

Such a device is generally called as a pressure regulator. They come in many stages to suit your upstream and downstream pressures. Don't expect to keep 2 bar pressure though the pressure in the cylinder drops below 2 bar. No need to put any extra tanks.

The device looks like this,

http://www.chem.agilent.com/Scripts/PDS.asp?lPage=1577

They will be much cheaper than you expected.

However, I am still puzzled.

 

[carheight]

Quark, you are a star. Thank you very much.

Sorry I didn’t explain myself very well. All what I simply need is to reduce 230 bar to 2 (if I’m using my diving cylinder) or 10 bar to 2 (if I’m using a simple tank from any DIY store).

I’m hoping to use my diving tank (or similar) to power my airbrush. I’ll let you know how it goes (with pics if can).

Thanks again. Daniel.

 

[davefitz]

I would think twice before connecting an LP tank to the 230 bar tank. You need to be real sure the relief valve on the LP tank will relieve more flow than can enter from teh 230 bar tank- there have been many failures of LP tanks whensimply using a single pressure regulator valve.

 

[zdas04]

The pressure regulator you need is the same technology you breathe through when you dive (you really don't want air at 230 bar in your lungs). You might be able to modify one of those that you already have to give you 2 bar instead of 0.1 bar.

Regardless of where you get the regulator, you need to make sure that your air source is either absolutely dry or you have some sort of filter upstream of your regulator. I fed an air brush moist air through a regulator once and three ugly things happened pretty quickly: (1) the Joule-Thompson cooling caused some water vapor to condense and the water spots ruined what I was painting; (2) the regulator froze and started spitting air as the dP broke the freeze and then refroze (globbing paint out the tip); and (3) a rubber O-ring in the regulator failed and I threw the damn thing away. Diving air is certified dry and oil-free so that source should be ok, you intermediate-pressure source needs to be checked carefully.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The Plural of "anecdote" is not "data"

 

[hacksaw]

you need a two stage regulator as a minimum, but instead of using a diving tank get a proper bottle for compressed air, one that matches your new regulator.

 

[davefitz]

I believe the name given to a single regulator used to connect a high pressure tank to a low pressure tank is a
" suicide valve". I first heard this term used in the air conditioning industry when some technicians would purge air conditioning systems using nitrogen tanks, and blown dryer tanks were the typical result.

 

[carheight]

Thanks for the advice gents, much appreciated.