Making an air LIFT

[Whittman]

Sorry, ref. the last post, I meant an air lift. Would appreciate any info and input. Thanks.

 

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[Dinkydick]

Here are some pic of a 2-inch I built. It was 20-feet long.

Dinkydick

 

[SEAHUNTER]

Dinky
What size compressor did you use and in what depth?
Seahunter

 

[southern maine diver]

Hey Dinky...

The 20 ft length and the curved exhaust I assume, was to raise the debris to the surface? Possibly to screen the sandy debris for coins? Relics?

How well did the 2" pipe work as compared to 3" and 4"? How deep were you working this?

Thanks for helping,

Wayne

 

[Dinkydick]

The airlift I constructed was for taking bottom samples for radioactive
sediment. It was built small because of the boat I was using. I ran it off
a SCUBA bottle (80 cuft) which lasted about 5 to 7 minutes. It did the job.
I used SCH40 pipe as this is what I had on hand. SDR or thin wall pipe will
work just as good and will be lighter to carry. The airlift was not glued
together because of space limitations. The loops of wire ties held the airlift
together when it was put in service. A smooth curving exhaust is a must.
Do not use a sharp 90-degree elbow as it will affect operation of the airlift
and put additional loading on the suction end and slow down the lift. If you can
keep the exhaust end at the surface or below the airlift will work best. An overall
length of the airlift pipe of 10-feet is sufficient for the lift to work. You MUST
keep the pipe vertical in the water for it to work. The compressor requirements
are the only thing which needs to be somewhat right. Airlifts work on air
volume and not on air pressure. In 20 to 30-feet of water a 45psi air source
will work but you need atleast 15 to 20 cfm. This is the problem. Compressors
with large volumes are LARGE. I leave this up to you for a compressor solution.
Most of my airlifts were ran off of rotary screw compressors which have volumes
of 125 cfm and above so I always had plenty of volume. Larger pipes require
larger volumes.

Hope this helps.

Dinkydick

 

[Whittman]

I was thinking about a 4 to 6" diameter pipe and will be working in about 18 to 25' of water. I'm wondering what a reasonable compressor would be? What would my minimum CFM be? If I get too large then I'm defeating the purpose of utilizing a lift on a small boat. Anyone know where I can find guidelines regarding CFM to depth ratios? Schematics and/or plans would also help.

 

[Skimmer]

We constructed a 4" flexible pipe (spiral re-inforced) for use in 50-60 ft water on the Margarita site for emerald recovery....it worked really well, but we had a HUGE Ingersoll-Rand compressor,
like the kind yousee on the side of the road on wheels being used with jack-hammers to break concrete. I'm sorry, I can't find the CFM in my notes right now, but it was (I think) around 150.
Man, that thing would give you a RIDE if you turned the valve controlling it before youhad it buried in the sand bottom!! We had to stop sucking every 5-10 minutes because its output (sand, rocks, shells....and sometimes emeralds...) would bury the aft deck of our workboat, and overwhelm the sorting screens. ( Which varied from bread racks size to chicken wire and then to smaller actual screen) Good luck with your endeavor! Mike

 

[ScubaDude]

The best place for you to start if you plan on working from a small boat and getting any effective work done is figure out exactly how many CFM you've got to start with and work it backwards. unless you've got a big boat that can support a large diesel rotary screw compressor like Skimmer is talking about i.e. 185 CFM your not going to be able get much done with it, or pile of scuba tanks and a good back. Unfortunately there is not much of a cost effective happy medium in self powered portable compressors. Your best bet as already suggested might be using an induction dredge such as Keene makes.

 

[sherpa t]

I am going to toss this out there, the last time this was discussed I had just returned from a weekend at Seahunters and an idea popped into my head. For a shallow application (like at seahunters). A commerical ( gas powered ) back pack blower ( what a lawn service would use ) mounted up in a little frame. As posted the volume is more important then the pressure, and a reduction in diameter down at the turn will add a bit of volicity / pressure. This should be a pretty easy to do experiment to see what it might or might not do. Some of these units have some pretty big outputs.

 

[Peg Leg]

THIS IS VERY VERY INTERESTING.
I have a gas powered weed blower that I use to provide the volume of air form a blast furnance that I used to use. The end opening was about 2.5 inches in dia. It was able to put out a 110 mph wind. It had a second setting that was able to put out about 40 mph wind.
I guess this means nothing untill I can figure the volume of air. My wife is looking for device right now.
THIS is a GREAT IDEA.
THANKS
Peg Leg

 

[ScubaDude]

Not enough pressure, you need at least 20 to 30 psi or more at depth for an airlift to function, then an additional 1/2 psi per foot of depth. Also remember that volume is a function of pressure.

Take your leaf blower and taper down the output and try to inflate your car tire, it ain't gonna happen captain.

 

[Salvor6]

I made this 2" airlift to work off my power inflator hose. No hose to the surface required. It works pretty good. Instead of one hole going in the side, the band has about 50 small holes going all the way around. This reduces the bubble size and makes more small bubbles. The result is a 2" dredge acts more like a 3" dredge.

 

[sherpa t]

Brad, Look at Echo PB650 - 63.3 cc engine. Not on a good monitor so the numbers are to fuzzy to read, but the small one ( 44 cc ) looks like 10.3 cubic meters / min. the 63 cc is larger but I can't make it out. Scott is working 10 to 12 feet of water so that would add 5 to 6 psi, not arguing with you cuse I don't have knowledge to do that, just pointing out I meant commercial not general home owner units.

 

[Salvor6]

Hey Skimmer, I built a 6" airlift in Key West to dredge for emeralds on the Atocha site. It used the same principle, a stainless steel band around the tube with 150 holes around. The compressor we used was a 110cfm unit. Heres a picture of the dredge on top of our 100' salvage boat. Notice the compressor in back. I didn't know anyone dredged for emeralds on the Margarita site. Find any?

 

[ScubaDude]

No, I didn't take it the wrong way. At 10 Cubic meters per min that equates to about 350 CFM.

Boyles Law say PV=PV
1psi x 350cfm = 35psi x V
V=10 cfm assuming perfect efficiency

I just don't think that a leaf blower is built to tight enough specs to develop the kind of pressure and volume required. It would be very simple to find out; just cap off the output and put a pressure gauge on it. Or taper down your output to a reasonable sized hose and take it underwater and see how deep you can go and still deliver air.

 

[Peg Leg]

The leaf blower that I have puts out 400 cfm.
Before I start please tell me the principle behind how this device works?
Thanks
Peg Leg

 

[Peg Leg]

I also have a small compressor that is electric now all I have to do is hook it up to a gas powered generator.
All I need is to go dwon 5 to 6 feet and it all sand with no rocks.
Peg Leg

 

[rgecy]

400cfm but thats at almost 0 psi. Once you apply some pressure, that will drop substantially.

I like Brad's idea to test it. Hook it up on a long line and go straight down to about 60'! Let me know if you make it back up!

 

[ScubaFinder]

Yup, proper CFM makes the airlift work effectively, but only PSI lets it work at the depths you need. I tend to agree that the tolerances in a leaf blower, even a really good one, are not sufficient to push decent CFM even at the shallow depths you are talking about. Want an even easier test, fill up a 55 gallon drum with water, fire up the leaf blower and stick the nozzle all the way to the bottom. I bet it stops (or almost stops) bubbling before it gets 3 feet down. Try it and let us know.

Jason

 

[Whittman]

Well, I think that you guys have anwsered my question for me. For a small boat application I think that a water dredge would be more efficient for moving sand. I don't think I'd be able to get a compressor big enough on a small boat. I guess if this stuff was easy everyone would do it!