Replies

1. 
   gweisenburge | May 21, 2002 07:36pm | #1

   John,

   I've used high pressure air tanks to power nail guns, but I'm not so sure they contain enough air volume to spray even small projects. HVLP requires a LOT of air. When volunteer fireman, I used 1800-psi breathing apparatus (BA) tanks to power "Jaws of Life" cutting tools, as well as other emergency equipment. The relatively small bottles have a regulator that delivers controllable pressures up to 120-psi, and they're usually equipped with a backpack and 6-foot hose with a quick connect fitting for tools. It can't be beat for trimming, because it contains enough volume to work all day without making noise or having to drag around lots of hose. Nail guns, however, require far less air than spray equipment. And where an 1800 to 2600-psi BA tank is relatively small and portable, I think a 3500-psi SCUBA tank is only back-packable when I'm under water. I wouldn't want to manuver one around the shop or job site while while trying to produce a quality finish. Finally, unless you're a licensed SCUBA diver or a firefighter, you'll have difficulty refilling your tank.

   All that said, I've gotta say that it might be worth a try. So let us know if you do.

   Gary

   
   

   ---

   Edited 5/21/2002 1:01:18 PM ET by Gary Weisenburger

2. 
   StanleyNiemiec | May 21, 2002 08:06pm | #2

   John and Gary:

   I cannot think of anything more dangerous than using compressed gas tanks to power sprayers and nailers.  If the regulator fails or malfunctions, the tool you would be holding could become a bomb and literally explode in your hand.

   I wrote an Extension Publication on Pneumatic Nailers.  During that research, I read through most manufacturer's literature and I believe all the manufacturers recommended that their tools never be hooked up to high pressure tanks.  If you use a gas like oxygen, any spark, like the driver striking the nail, could cause the oxygen to ignite.

   There are reasonably priced air compressors for spraying that are a worthwhile investment.  To cobble something together with the hope of saying a few bucks is "penny-wise, pound-foolish" thinking.

    

1. 
   gweisenburge | May 21, 2002 08:55pm | #3

   Stanley,

   SCUBA and BA tanks don't contain pure oxygen, they're filled with air, the same mix you're breathing as you read this. Think about it:  neither a firefighter or diver can breath pure oxygen. A firefighter certainly wouldn't bring pure oxygen into a burning structure! Secondly, high pressure air tanks have powered firefighting and scuba tools for a long time, and its dangerous to misuse or abuse any tool, such as a high pressure air tank or its regulator, as well as a standard small shop compressor. We all should know the danger of rusted compressor tanks.

   To use or have a high pressure air tank filled, you've gotta be a licensed and current SCUBA diver or a firefighter. Either way, one would have to learn about and maintain a high respect for the equipment. Your caution should be heeded, but I think you're being just a little too paranoid.

   Gary

1. 
   UncleDunc | May 21, 2002 10:36pm | #4

   There are a couble of risks here. One is a literal bomb, high pressure air with combustible finish. I suspect that compressed air is not a great deal less dangerous than pure oxygen in that regard. Using a waterborne finish will eliminate this possibility.

   Another is just overpressure. Having your paint pot blow up in your hand would feel very like a bomb even if the pressurizing gas was something entirely inert, like argon. A pressure relief valve just downstream from the regulator should take care of it. Or two if you're feeling particularly paranoid.

   Edited 5/21/2002 3:37:22 PM ET by Uncle Dunc

2. 
   JohnKrist | May 21, 2002 10:44pm | #5

   Thanks for the replies and thoughts.

   I guess what I am really asking is: "How feasible is it to rig a regulator between a SCUBA tank and a HLVP gun? Both spraying and breathing off scuba have very similar needs: stead flows of air, on demand. The "on-demand" part is the tricky bit: in SCUBA, the regulation of air occurs in two phases: at the tank and at the mouthpiece, hence the name "two-stage regulator". I have no experience in HLVP pneumatics, but the need seems to be the same. I should figure out how a gun and its compressor work first, but it can't be that complicated in principle. Cousteau figured it out as a teenager one summer in Lake Champlain in VT, working out of his garage with a buddy...

   Thanks very much for the feed back and I will report what I can find.

   Thanks,

   JK

1. 
   gweisenburge | May 21, 2002 11:48pm | #7

   Try this forum:  http://www.scubaboard.com/f13/s. I don't think you have to register to view messages.

   Edited 5/21/2002 5:08:52 PM ET by Gary Weisenburger

3. 
   Elcoholic | May 21, 2002 11:32pm | #6

   I don't see a problem other than volume.  Not being a SCUBA guy, I'd look into a nitrogen tank and a good welding regulator.  I used to use a 3000# Q-bottle of nitrogen and a high-precision regulator to calibrate pressure transmitters and switches in petro-chem plants.  Way better than a dead weight tester.

   John O'Connell - JKO Handcrafted Woodworking

   Life is tough.  It's tougher if you're stupid - John Wayne

4. 
   PaulReuter | May 22, 2002 01:32am | #8

   When I started diving, the tanks were galvanized & held 72 cu.ft. at 2250 psi.  The newer aluminum tanks held 80 cu.ft. at 3000 psi.  Assuming you have a tank & can find a regulator that will fit the valve that is unique to scuba I believe that if you work out the cfm requirements for whatever use you are making and factor in the cost of refilling the tank,  you will find a compressor to still be the less expensive option.

   Paul

5. 
   JasonMI | May 22, 2002 01:56am | #9

   I have to ask what systems you're looking at that the gun price versus air supply price are so out of whack....I've seen half-way decent HVLP conversion guns (which is what your talking about, right?) starting at say $250 up to about $800, so depending on the gun model, you might be a lot better off, as one poster suggested, getting a less expensive compressor (if you want to go conversion). Also, you didn't say what you wanted to do...if woodworking or auto work or something else is leading you down the HVLP path, then it might make sense to start thinking about the compressor to run other tools you might use at a later date.

6. 
   Paul_Snyder | May 22, 2002 04:10am | #10

   HVLP stands for high volume, low pressure. The spray gun uses a lot of air (high volume) to atomize the fluid instead of high pressure.

   The pay-off is a lot less overspray and wasted material. Your tank will power the spray gun very briefly. A compressor is a must.

   Paul @ First Finish View Image

1. 
   Froed | May 22, 2002 01:17pm | #11

   If I remember correctly, a scuba cylinder's stated volume is actually an equivalent volume based on atmospheric pressure.  So an 80 cu.ft. tank (usually closer to 77) will last less than 10 minutes with a gun requiring 7.5 cfm, depending on the pressure drop required at the nozzle, length of the hose, etc.

   I don't see that it  would be more dangerous than a compressor, assuming that it is maintained and inspected like a typical scuba setup, but as someone said, you would probably need to be certified to get it refilled.  Kind of a neat idea, but I don't think it's too practical unless your spray sessions are very brief and very infrequent.

   Froed

1. 
   JohnKrist | May 22, 2002 03:13pm | #12

   Great analyses.

   While I've two tanks and can get the air, it clearly seems that the compressor is the way to go. A fill costs about $5 minimum, plus time and trouble. At $5/10 spraying minutes/tank, that's just 40 hours of spraying for a $200 compressor. As I will likely move all finishing to HVLP, it makes sense to get a compressor.

   Thanks for putting it all into perspective.

   JK

1. 
   Elcoholic | May 22, 2002 11:05pm | #13

   I have a 4hp/30gal/11cfm @ 90psi compressor and a very good conventional Binks #95 gun.  I am very seriously considering switching over to a LVLP conversion gun.  On the other hand my buddy swears by his turbine set-up and watching him spray a few times has really impressed me - no overspray and most importantly, absolutely constant delivery pressure/pattern control.  He uses mostly Enduro Poly.  I will be borrowing his set-up in a few weeks to spray 14 High-back Stickley chairs I'm building  for him.  If his new non-metallic gun lives half-way up to his claims it'll be clinched for sure.  I'll probably build the turbine housing myself as he did.  They have replacement turbines at Graingers.  If I can put it all together for $500, a 50% min. improvement in transfer efficiency will save $27.50 per gal of finish at $55 gal.  The new set-up will pay for itself in 18.2 gals, even ignoring labor and energy savings.

   Whatever you do don't make the same mistake I did.  Don't be cheap and buy an oil-less compressor.  They are obnoxiously noisey and as they wear the CFM numbers start to fall.  I won't be disappointed when mine gives up the ghost.  If you're going to get a compressor just for spraying, don't.  Go turbine.  Conversion guns just aren't as good or efficient or so I'm told.  If you want a good convential gun despite the limitations let me know, I'll make you a deal.John O'Connell - JKO Handcrafted Woodworking

   Life is tough.  It's tougher if you're stupid - John Wayne

1. 
   Biscardi | May 23, 2002 06:26am | #14

   I think you could paint better with the scuba tank at 96 feet below the surface as the air in the tank would be at 3 atm. Over spray would be less of an issue as the tide would carry it off.

   Nothing worse than tentacle marks in the finish though.

   Frank

2. 
   sschefer | May 23, 2002 08:09am | #15

   O.K. Frank,,  I got it... By the way, would that be three violations of Martini's law? Up or down? Just watch the bubbles and don't forget to stop and get rid of some of that extra nitrogen.

   Steve - in Northern California

   Edited 5/23/2002 1:13:46 AM ET by Steve Schefer