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AVarouxis@ao*.co* Jan 2, 95 02:15:22 pm -0500 Precedence: bulk Errors-To: owner-techdiver@opal.com Date: Mon, 2 Jan 1995 14:15:22 -0500 To: techdiver@opal.com Subject: Air Lift question What capacity air compressor is required for an air lift to operate efficiently at 110 ftsw in an overhead environment. ***end quote*** Unless you are totally wedded to the idea of an air lift, I would suggest a water venturi dredge would suit your needs much better. They are similar to an air lift in construction, but they use the force of highish (100 odd psi) pressure water (like a firehose) to drive the flow rather than the bouyancy of air. They work at any depth and don't pollute the water like an air lift. (normal air compressors introduce quite a lot of oil into the air flow to lubricate the air powered tools) Another advantage is that they can be used at any angle, and so the spoil can be moved much furthur from the work site. With an air lift it will rain down almost on top of you. (beware of big rocks falling on your head) Don't forget that both methods will result in *zero* vis. Another possibiliy is a suction dredge. These can be hired, as can the hoses, but they are quite difficult to manouver. I have used this type of dredge 150 metres up a pipe and found it a bit of a bother, (but not impossible, just count on 70 litre/minute gas consumption) If you are totally commited to an air lift then you should need around 1000 cfm for a 4 inch dredge (ie small) or in metric thats 30 000 litres/minute (500/sec) at about 10 bar for a 100 mm dredge. Make sure there is a dead man switch on any gear you make up, and be *very* careful. Dredges eat divers. (this is not a joke, it is a warning!!!) Never let go of them, except air lifts. If an air lift blocks up it will head off for the surface. You have the choice of riding it up, (bends-embolism-violent contact with the roof) or letting it go and hoping that when it comes back down it misses you. I wear a minimum of 60 lb (30 kg) *extra* lead on my belt when working an air lift. You may want to tie it down as well. With any dredge make sure that you don't use any part of your body or equipment to block it with. This is *very* important with suction dredges. The one I was using had 200 metres of 150 mm pipe. That means about 3 tonnes of water in the pipe, travelling god knows how fast. Imagine using your head to stop that with!! Let me know how you get on, Jason (gasdive@sy*.DI*.oz*.au*)
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