Booster question

[Jimmer]

A few friends and myself are thinking about setting up a home mixing station, and I was just curious how low you can realistically scavenge an O2 cylinder. Let's say for example a good 2 stage unit.

Thanks,
Jim

 

[cool_hardware52]

A few friends and myself are thinking about setting up a home mixing station, and I was just curious how low you can realistically scavenge an O2 cylinder. Let's say for example a good 2 stage unit.

Thanks,
Jim

Like all things associated with O2 there is no absolute answer.

The final pressure in the supply bottle is a function of patience and availability and cost of drive gas, and the availability of more O2. As the supply gas pressure falls and the output pressure rises the amount of drive gas used per cuft of gas "shifted" goes up dramatically.

So does the heat generated. The pressure ratio, i.e. the outlet pressure / inlet pressure impact the temp rise.

If you are draining a O2 cylinder to PP fill an empty 2400 psi tank for 32% you only need about 336 psi of O2 in the scuba tank. Boosting O2 from 200 psi to 336 is pretty easy. OTOH if you are trying to boost 200 psi O2 into a 3k deco bottle you need a lot of time and drive gas.


The temp gain hurts in two ways, Hot O2 is not desirable from a safety standpoint, and it makes it harder to estimate the final pressure in the bottle you are blending into.

Higher temps also put the booster seals at risk.

Fortunately O2 is relatively inexpensive so there is little incentive to try to get much below 200-300 psi.

Tobin

 

[pescador775]

The AGT 15/30 or its clone will really jam oxygen, a lot faster than recommended by some of the usual suspects. Flow can be reduced or increased by metering the drive air. It has a flow through feature so there is no drive air requirement until the storage bottle and fill bottle equalize. The booster is two stage with interstage cooling. I've never noticed any heating of the system but wasn't really looking for it either. Bear in mind that tapping a storage bottle of oxygen has a cooling effect which is most pronounced at high source (oxygen) pressure, and that when pumping from lower source pressures, rising pressure ratios are inversely correllated with quantities (mass) of gas compressed. The AGT 15/30 will draw down to a couple hundred psi.

 

[cool_hardware52]

Bear in mind that tapping a storage bottle of oxygen has a cooling effect which is most pronounced at high source (oxygen) pressure,

Cooling by expansion will occur at the point where the pressure drops and the gas expands.

That's almost never where you'd like it to occur in the system.

Heating of the booster, or boosted gas is of little concern when the supply tank is near or above the outlet pressure, as little increase in density takes place.

Heating is concern when the inlet gas pressure is low and the outlet gas pressure is high, as when one is trying to scavenge a supply bottle to as low a pressure as possible.

Tobin

 

[pescador775]

Cooling by expansion will occur at the point where the pressure drops and the gas expands.

Yes, gas which is supercooled at the orifice of the valve is moving too rapidly to become isothermic at that point. The gas remains cold and continues to extract heat after it enters the first stage of the system. Such is why a fire extinguisher can be used to freeze a snake.

 

[Gilldiver]

Back to the original question,

First any booster will run between about $1,500 used to up to $10,000 new depending on size. Then you need to factor in is the energy (electricity) to run the low pressure/high volume compressor need to drive the booster and the size/cost of that compressor. You will not run any booster very well from a Home Cheapo $110 compressor that is meant to run a nail gun etc. If you plan on doing a lot of mixing, you should have one of the 60+ gallon two stagers that can keep up with a spray gun. These tend to be 220-240 volts and run around $350-$500 plus the cost of the service.

What you will most likely find is that O2 is cheep compared to these costs unless you plan on doing a lot of 50 and 100% fills or are topping off on tanks that have 1,000 psi or more in them already.

Where a booster really comes in is with He mixes as now your cost of gas and ability to top off are much more costs effective.

I'd love to get a helium booster, but the number of times I need to do higher then 35% He a year just will not justify it. So, I just dump and fill usually putting in less then 400 psi O2 and what ever I need for He. I also do a number of 50% tanks at a time and use the high press O2 to get what I need for them first.

By the way, I run 3 x 300 cubic ft O2 and 4 x 300 cubic ft He in my cascades. Buy the tanks and don't pay for rental, after a year or so the rental savings have paid for the tanks.

 

[cool_hardware52]

Yes, gas which is supercooled at the orifice of the valve is moving too rapidly to become isothermic at that point.

Maybe, maybe not. Nothing requires that the gas be moving rapidly. Consider a simple decanting whip with a needle valve. The needle valve controls the transfer rate, and is in effect a manual pressure "regulator". It's also where the gas changes pressure.

You will have some cooling of the supply bottle, and some heating of the tank being filled, but the heat lost in the supply bottle won't equal the heat gain in the tank being filled. Why? Because of the cooling that takes place at the needle valve.

The gas remains cold and continues to extract heat after it enters the first stage of the system.

Yes, in the case of a supply bottle feeding a booster it quite possible that the inlet check valve on the booster is where the gas will see a pressure drop. That's useful as it is cooling the booster.

Such is why a fire extinguisher can be used to freeze a snake.

I'll keep that in mind. Bird shot in a .22 works pretty good if I miss with the shovel.

Tobin

 

[Jimmer]

Back to the original question,

First any booster will run between about $1,500 used to up to $10,000 new depending on size. Then you need to factor in is the energy (electricity) to run the low pressure/high volume compressor need to drive the booster and the size/cost of that compressor. You will not run any booster very well from a Home Cheapo $110 compressor that is meant to run a nail gun etc. If you plan on doing a lot of mixing, you should have one of the 60+ gallon two stagers that can keep up with a spray gun. These tend to be 220-240 volts and run around $350-$500 plus the cost of the service.

Don't worry, I'm well aware of the requirements for a booster, I just wanted to know how well they scavenge. I already have a 60 gallon 20cfm 220 volt compressor in my garage, that i built myself, so I should be fine. If we're going to be getting into deco diving (a few of the guys already are) we will be needing 50% and 100%, and the nearest place that boosts is over an hour drive away. Which means either dropping off and going back to get it, or waiting a while and basically wasting a whole lot of time.

 

[rjack321]

I have a 3cfm compressor and its alot more useful than a booster. I can transfill the O2 for my 50% (top with air) and 100% and then continuous blend all my other mixes. Air, 32%, 30/30, 25/25, 21/35, 18/45 and I sometimes pump 100% He though it just fine.

 

[Gilldiver]

Don't worry, I'm well aware of the requirements for a booster, I just wanted to know how well they scavenge. I already have a 60 gallon 20cfm 220 volt compressor in my garage, that i built myself, so I should be fine. If we're going to be getting into deco diving (a few of the guys already are) we will be needing 50% and 100%, and the nearest place that boosts is over an hour drive away. Which means either dropping off and going back to get it, or waiting a while and basically wasting a whole lot of time.

Then have fun, you should be able to pull down to 300-500 psi before you start running to many cycles in the booster.