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post #15 of Old 01-28-2013
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Re: DIY - discussion on building a DIY hookah diving compressor

Let's slow down a bit here.

If you are unfamiliar with safe diving principles, then please take the time to learn them. It's not rocket science, and ultimately can make the difference in whether or not you injure yourself or do long term damage to your body. If you don't want to shell out the money to get certified, at least find the texts that go with a cert course that will lay everything out for you. At a minimum, learn how to read dive tables and know what the concept of bottom time really means.

If you want to go with a remote tank set up, then most places are going to want to see a cert card when you take your tanks in for a fill.

A couple of things mentioned got my attention.

There is one drawback to this idea: You need the weight of the tank to actually get and stay under water; some even need extra lead besides the tank.
Without that weight, you bob up like a cork, or have to paddle like crazy, just to stay under water.
This is actually incorrect. Buoyancy control when under water is a continuous process. One of the forces at play is the air tank (others are the water density, your own body composition, the amount of gear you carry, the size and type of exposure protection you wear and at what depth, etc.) When a dive tank is full, it is negatively buoyant -- i.e. is acts as a weight. As the tank empties, it becomes negatively buoyant -- i.e., it acts as a float. Using a remote air supply removes the changing buoyancy variable of the tank.

I have a 30ft hose on one of my tanks, I carry on the boat. I have a yoke to hook (2) tanks together, but haven't had the need. Remember, even a 'hooker' rig has 'bottom' time, don't get into trouble by thinking you can STAY down forever,(like cleaning a couple of hulls at one time). .02
AirborneSF and Minnewaska are both right. Here's a table that shows the increasing water pressure at the depths we're talking about:

As you can see, even at the relatively shallow depths we are talking about you need to consider overall increased nitrogen absorption. But as Minne mentions, rarely does the absorption level reach something that must be taken into account. Most recreational dive tables set 120 minutes as a max bottom time for depth of less than 1 atmosphere (1atm, or <33').

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