Compressor for scuba tank

Nullifier

Expedition Leader
#1
So an odd question but What type of compressor that is vehicle friendly and what other psrts would I have to get to be able to fill a scuba tank from the truck? I do not think my viair would cut it. An oasis? myself and my friend were talking last night about baja and thought since we were taking our sit on top kayaks we might bring our scuba gear to do some diving from the kayaks. My guess is that there is some great stuff in alfonsia and other areaas that are undiscovered.
So how do we set up a refill system on the taco without mounting an industrial compressor
 

HenryJ

Expedition Leader
#2
None of the above.
SCBA tanks are filled to 2216 lbs for the low pressure bottles and 4500 lbs for the high pressure bottles. Most compressors will never get a tenth of that pressure.
This is also a breathing air compressor. That means there are special lubricants that are used and quality standards that must be met for safety. All the compressors that I have seen needed at least a forklift to move them.

A better idea would be a cascade. Several bottles larger than yours. Filled to a pressure that meets or exceeds yours. Fill from the first and top off with the next. Done properly you can fill many bottles. Regulators and gauges should not be hard to find. Finding a shop or department that will fill it for you may be a different story.
I fill mine at our fire department, of which I am member.

Have you considered joining your local fire department? It does have advantages :luxhello:
 

robert

Expedition Leader
#3
Good call on the volunteer FD- I was going to suggest the same thing. I can't imagine the cost being worth it for an individual- you can buy a lot of tanks for what one of those is going to cost you. They are also BIG and heavy. To operate safely, the apperatus has a steel cabinet in case there's a rupture. Not something you are going to be mounting in the bed of a Taco.

This will give you an idea what they look like
http://www.americanairworks.com/cas-mobile.html
http://www.divesports.com/cascadesys.htm
 
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#4
Max-Aire 35

I can't find the data for the portable compressor that we had on our sailboat, but it was similar to this one:

http://onlinescuba.com/eshop/10Expand.asp?ProductCode=45005B

Weighs 85 lbs, but costs around $3,000!

I saw a small portable compressor that ran off of 120 AC used by some travelling divers in Ecuador several years ago but I can't find information on it. As I recall it was small, wouldn't reach the maximum pressure of a modern aluminum bottle, and took a long time to fill a bottle, but it did allow multiple dives in really remote areas.

Some sailboats have engine-driven compressors fitted to their main engines or generators and they use these compressors to fill tanks. Again, I don't have any specific information - sorry.

These guys make a 12volt hooka set up that I've seen some boaters carry aboard for cleaning the bottom, clearing fouled props, etc. Might not get the depth you want (athough they have other floating models also):

http://onlinescuba.com/eshop/10Expand.asp?ProductCode=45002A

Howard L. Snell
 
#5
Volume of SCBA

How much air does one of these SCBA tanks hold. Such as how many tires can they fill without having to be refilled. My fire department has a few that they are going to get rid of. Just wondering if it is actually feasible to use these in place of say a CO2 tank. Sorry for the hi-jack.
 

HenryJ

Expedition Leader
#6
GulfShoresFJ60 said:
How much air does one of these SCBA tanks hold. Such as how many tires can they fill without having to be refilled. My fire department has a few that they are going to get rid of. Just wondering if it is actually feasible to use these in place of say a CO2 tank. Sorry for the hi-jack.
The cubic feet of air available is significant and more than a equally sized CO2 system.
IIRC Co2 has less pressure. It also is colder than air when rapidly released, so it may expand differently.

The storage volume for a compressed gas can be calculated using Boyle's Law: pa Va = pc Vc (1)

pa = atmospheric pressure (14.7 psi, 101.325 kPa)
Va = volume of the gas at atmospheric pressure (cubic feet, cubic meter)
pc = compressed pressure (psi, kPa)
Vc = volume of the gas at compressed pressure (cubic feet, cubic meter)
I have a 1 hour high pressure composite bottle. My best estimate would be 306 cubic feet of air at 35 psi.

Now the bad news. I have not had luck finding a high volume/high pressure regulator. We have a 2216 psi regulator that is used for the air chisel on the rescue. A regulator like that might work and I would just have to limit filling the bottle to 2216 psi. That cuts the volume in half. I haven't had any luck finding one of those regulators either.
I will admit that I have not been looking hard lately. I can find high pressure regulators and have a couple already. They are not high flow though. Then you have the issue of the correct nipple for connection to the tank. Breathing air connections are different than everything else. Hard to find surplus.
So far it seems that you could purchase a commercially built CO2 system for less than the parts needed to reuse old SCBA cylinders.
 

robert

Expedition Leader
#7
My guess is that if the fire department is disposing of them that they are no longer passing their hydrostatic testing. If this is the case, they are only worth scrap.

They are easy to attach to the low pressure line on your octupus though:
http://www.diversdiscount.com/resources/frameset-search.asp

As for using them to refill tires, here's an article about them:
Some guys have been known to bring scuba tanks out on the trail for air tools, because it works and it is cheap - but I wouldn’t recommend it. Unlike liquid filled CO2 tanks with constant gas pressures of around 800psi, a scuba tank is typically filled completely with highly compressed air that starts at pressures in the ballpark of 3000psi, and goes down steadily as you use air. A scuba tank will also run out much more quickly than a CO2 tank, because gas takes up more space than liquid; a large CO2 tank fill will outlast 10 scuba tanks of the same size. Between the safety advantages and the greater capacity, CO2 wins this battle hands down... in my opinion, a full scuba tank on the trail is a bomb or missile waiting to happen.
http://hummer.off-road.com/hummer/article/articleDetail.jsp?id=263809
 

HenryJ

Expedition Leader
#8
Good point. I had not taken the liquid CO2 into consideration. As to the bomb aspect of the firefighters SCBA tank, that is a bit harsh. These are very durable and probably exceed safety standards of a SCUBA tank.
They are designed to be dropped off the back of a firetruck at full speed and not blow up, as well as handle extreme temperatures. I am very comfortable with their durability. The regulator added would be in question though. I do not know how durable it might be. That could be a risk.
Aluminum Cylinders can be hydroed indefinitely. They are very heavy 2216 lb bottles. Many departments have gone to the 4500 lb high pressure systems. The old aluminum cylinders are being surplussed. The composite bottles have a lifespan and are taken out of service at specified intervals regardless of hydro status. It would be nice to find a use for the surplussed bottles, other than lamps and bells.

All that said, I still don't think they are going to be of value for air tools or tires. They are heavy, it is an extremely high pressure vessel, refilling may be an issue, parts are expensive and difficult to find. It is just not going to pencil out. When all signs point to difficult, it is usually better to take an easier path.
 
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robert

Expedition Leader
#9
I thought the comment about them blowing up was pretty funny too. :iagree: I've seen some severaly abused looking tanks that were still perfectly functional. Some of the volunteer depts around here use equipment like the Marine Corps- it gets rebuilt long after parts are no longer available and right up until the old guy who used to be able to cobble it together in his farm shop finally dies. :xxrotflma

If you are just looking to inflate tires or run air tools, you can get used steel CO2 tanks pretty cheaply from restaurant supply places- they are used to pressurize the drink systems. Your local welding supply place can usually fill them cheaply; they are heavy though.
 

HenryJ

Expedition Leader
#10
robert said:
...you can get used steel CO2 tanks pretty cheaply from restaurant supply places- they are used to pressurize the drink systems. Your local welding supply place can usually fill them cheaply; they are heavy though.
Soda pop fountains use CO2 tanks that are light weight aluminum. They also have a protective handle around the tank valve. The lower pressure gauges may be easier to find. Any welding shop will have that stuff. Many options there.
I still feel that an electric compressor with a virtually unlimited supply of air is the way to go.

We are headed off track for this thread.

The best solution for a remote fill station for SCUBA or SCBA tanks is a cascade. That is what fire departments use.
 

ntsqd

Heretic Car Camper
#11
Biggest issue with a high pressure tank isn't the tank rupturing (unlike air reservoir bumpers, sliders, & cages), it's the valve getting knocked off from rough handling or an accident.

Ever notice that Oxy-Fuel bottles on portable welding trucks nearly always have the regulators removed and the transport caps installed? There is or was a law requiring that, just for this reason. Having seen a cinder block wall that failed to stop a oxygen tank doing it's best imitation of a missile I can see the logic in that.
 
#12
Sorry to resurrect a long dead thread.
My LMTV has a compressor on board that generates 155 PSI (unregulate) and 120 PSI regulated air that is stores in 3 tanks already. I want to increase the overall air capacity so I can run air tools and an air horn. Adding tanks would be simple enough but I do like the idea of running a SCBA tank and storing the air at higher pressures because it reduces the system volume and makes an independent tank I can use without drawing down the main system used for the truck. I also expect the leak down to be non existent or very slow.

Looking on ebay I can find cheap HPA compressors used for paintball. I see other companies making 2/3 stage compressors. Has anyone looked into taking 120 PSI and making 4200 PSI by adding stages?
 

DaveInDenver

Expedition Leader
#13
Aluminum Cylinders can be hydroed indefinitely.
Can't all cylinders can be tested and recertified forever? I once got an oxygen cylinder, supposedly one of the surplus Nazi ones with a windowed swastika, with a first test of 1932. Its neck must have been re-stamped a dozen times.
 
#15
Sorry to resurrect a long dead thread.
My LMTV has a compressor on board that generates 155 PSI (unregulate) and 120 PSI regulated air that is stores in 3 tanks already. I want to increase the overall air capacity so I can run air tools and an air horn. Adding tanks would be simple enough but I do like the idea of running a SCBA tank and storing the air at higher pressures because it reduces the system volume and makes an independent tank I can use without drawing down the main system used for the truck. I also expect the leak down to be non existent or very slow.

Looking on ebay I can find cheap HPA compressors used for paintball. I see other companies making 2/3 stage compressors. Has anyone looked into taking 120 PSI and making 4200 PSI by adding stages?
Your LMTV should be more than capable of running air tools and an air horn off the tanks and compressor it already has. Air horns don't take much volume unless you're going to lean on the horn for miles, and even then your truck will probably keep up... The on board compressor probably rivals the output of a normal 5hp compressor. With that much output, even if you pull the tanks down a bit with an air impact, they recover very fast.

Just get a gladhand coupler and put an air chuck on it. I did this with my deuce and a half and it worked great. If you had a really stubborn and really large bolt, you might have to hammer on it a bit, then wait half a minute for the compressor to recover, but you'll get there, and for normal stuff it keeps right up, especially if you idle the engine up to 1500rpm or so. Remember, you're not driving AND running the impact, so if it pulls the system pressure down a bit, there's no worry.

As for "adding stages", you're again talking about a very expensive compressor setup. When you're pumping to 4500psi, starting at zero vs 120psi is moot. It's the higher stages that cost the big $$, and you can't just feed a normal compressor higher input pressure and get higher output without internals coming apart... (You're still asking the piston to compress against 4500psi...)