Small and Cheap HPA compressor

[[PX]Kal Bob]

I vote for a pressure relief valve over a burst disk if we can find one.
I like the idea that we can reset it if need be.

With the Burst / Valve I think one timer is more then enough.

[THE JEW (RaVeN)]

Sure, whatever's easiest. A burst disk I know we can find at any pb store. If we can find a relief valve cheap, even better.

[[PX]Kal Bob]

I updated the price to reflect the piston mod.

[[PX]Kal Bob]

Would something like this work?

http://www.alibaba.com/product-gs/34076 ... lator.html

[THE JEW (RaVeN)]

........uh?

viewtopic.php?p=34858#p34858

Not with those posted specs.

[[PX]Kal Bob]

lol, I knew I posted that somewhere!

I am not understanding the input would be 4500psi from the Shoebox and the output would be 3000psi to the Scubas.
The splinter would come before the valve for filling 4500 PSI Tanks.

[THE JEW (RaVeN)]

I'm basing my assumption on the fact that the air coming out of the Shoebox is at 4500psi. The max input on that reg is ~4300psi. If it's the type where it starts low and builds up, then maybe it would work.

What's the output psi of the Shoebox?

[THE JEW (RaVeN)]

Output fittings:

The hole the output fitting screws into is 1/8 NPT but the fitting itself is a male Foster.

Tom

http://www.shoeboxcompressor.com/forum/ ... ght=output

Fittings discussion:
http://www.shoeboxcompressor.com/forum/ ... ght=output

Stainless steel seems to be the way to go.

[THE JEW (RaVeN)]

How one guy set up his 4500psi unit to fill 3000psi:

http://www.shoeboxcompressor.com/forum/ ... ght=output

[[PX]Kal Bob]

I am guessing that the reg is over built and will take the extra 200 psi lol.

I don't get it, how is that rig limiting the pressure, it seams to only have a protector in it.

[[PX] Nebuchadnezzar]

I'm not too concerned about filling 4500psi as only a couple of us have 4500 tanks? I know I don't, and the SCUBA will only be used for 3000.

What is the price difference?

[THE JEW (RaVeN)]

You're betting that a high pressure, Chinese knock-off reg from Alibaba is over-built? Just want to make sure we're both on the same page here I actually think it'll be ok, but let me explain what I think we're up against.

I think the Shoebox output will be 4500 psi. I actually think it would be higher. Thus, the 7000psi burst disc on the 4500psi model.

DISCLAIMER:
My knowledge of the pneumatic transfer is limited to first year physics and a couple fluid dynamics courses. I'm going off of a semi-educated guess here. However, if you have reason to believe I'm off the wall state why and I'll change my tune.

I'm guessing that the way the tanks are filled are through pressure differences. Ie. One side of the circuit is higher than the other so it flows to the low side of the circuit. That's why I'm guessing the pump actually puts out around closer to 5000psi in low volume amounts. Ie. the 100psi gets compressed to a very small volume at 4500psi.

I'm banking on the system working similar to your lungs. Your lungs work by creating a pressure differential between themselves and the atmosphere. The diaphragm expands your lungs volume so that there's a lower pressure than the atmosphere. Thus, air rushes in until the pressure equalizes. The diaphragm then contracts the lungs to a smaller volume. This creates a higher pressure than the atmosphere so air rushes out.

If the pump can fill a tank to 4500psi, using the lungs as how I understand the pump to work, it has to be outputting above 4500psi. I'm banking on it being between 4650 - 5000psi (ie. around 1.5X to 7000psi safety factor).

Don't get me wrong here. If the reg is actually rated at 4300psi, we should be good (ie. it should be good to at least ~6400psi then). I just question whether it is or not. I guess there's one way to find out Truth be told, we can give it a shot and the side-effects would be minimal. If anything, just isolate the reg and then no worries. I can have my aerospace engineer/steam pipe fitting educated friend down and we can really set up the b!atch if there's still concerns.

There is no price difference between 3000psi and 4500psi. That's why I think the 4500psi model is the better value. Truth be told, the scuba's is probably good to 4500psi. I know it's good to 3500psi because that's what the guy at Adrenalin filled it to (ie. hot fill that cools). If we have a 4500psi source, I imagine people getting into hpa would buy that. The price difference is not all that great when buying used and you get 150% of the storage at the same volume. Almost all 4500psi tanks are carbon fibre now so that's another reason to get one (much lighter, stronger, less likely to deteriorate, etc.)

Look, don't get me wrong here. High pressure air isn't something to fark around with. However, proper care and a set procedure make it so that everything is safe. H3ll, we drive to work everyday at speeds that can easily decapitate us with a machine that is basically using controlled explosions of highly flammable fuel for propulsion. Nobody thinks twice about that because we do it everyday.

With all the safety precautions Homey B and I have discussed I'll feel more safe getting my tank filled at his place than at any licensed pb store.

Some of them include:

-timers in series (ie. if one doesn't work, the other will)
-dedicated breaker
-valve with relief and/or burst disc method
-locked key access
-placing the equipment in an area sheltered, but away from people
-only running it when people are not around

We could even go so far to make a water containment "field" if it's still a concern. That's how they do a hydro and if the guy who's in charge of watching tanks blow is fine with sitting beside a tank that he's stressing to around 7000psi with only about 5 inches of water and a thin tin shell between him and an air explosion, I think we'll be ok.

The first few times we'll need to watch it closely. Once the performance metrics are known, the procedure locked down, and only certain people allowed access everything will run smoothly. Quite frankly, I believe the safety concerns have been more than addressed. Now it's just about working out the fine details on how to get things done.

[[PX]Kal Bob]

You are probable right about the Shoebox and the wild pressures on the output side.
So we would really need a intermediary pressure tank (standard 4500psi HPA tank) to buffer the input.
At which point the cost is high enough that we should just go with the Electronic Pressure Switch option.

At the Moment I agree that the burst disk and timer is more then enough for fill safety.
Likewise I think the key power lock and locked cage for storage will keep us safe from operator error.
I think four authorized operators should be more then enough to cover missing people.

I have also been looking in at the best solution.
We could just snag a 440cf bulk storage tank.
I have found some on kijiji for 250ish. I am also going to give Air Liquide a ring as they may rent them for 50 a year.

Edit:
I just ran the 440 thru the calc you posted and after 20 fills you are still getting 3000+ psi.

Ps. I still have my eye on those 3 scubas, bidding war starts tomorrow

[THE JEW (RaVeN)]

At the Moment I agree that the burst disk and timer is more then enough for fill safety.
Likewise I think the key power lock and locked cage for storage will keep us safe from operator error.
I think four authorized operators should be more then enough to cover missing people.

Right, that's the cheapest, easiest, most KISS theory applied method that will work. Once we know the time, we should never need to replace the burst disk because we'd never need it. It's the "suspenders" that we've added to the "pants" that we're already holding up with two "belts."

We'd need a stainless steel T with valve (ie. fittings rated to 4500psi - 5000psi), a reducer to 1/8" NPT (I think that's the burst disc size), 4500psi - 5000psi burst disc, 2 timers, and we're good.

Q: Can I fill a scuba tank?
A: Yes but you have to provide a fill hose and attachment fittings. I estimate it will fill an 80 cubic foot scuba tank to 3000 psi in about 24 hours.

http://www.shoeboxcompressor.com/FAQ-s/faqs.html

How many cubic feet is our scuba?

If nothing else, set the timers for 12 hrs, start it at midnight and then check on it at noon. Then it becomes a game of drink a beer and see how the full the scuba gets. Then we have the time benchmark. Subtract 10% for safety if it's a huge concern.

[[PX]Kal Bob]

Found these on Ebay for 29 dollars
http://www.ebay.com/itm/Barksdale-Press ... 138wt_1204