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January 1997 Vol. 12, No. 1   RSS Feed for Undercurrent Issues
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USD’s Micra Air System

An ounce of prevention . . .

from the January, 1997 issue of Undercurrent   Subscribe Now

USD's Micra Air SystemOur equipment editor is a strong proponent of independent emergency air supplies. For several years he's carried a 6-cubic-foot pony bottle system on all his test-dive trips for In Depth. In this review, he checks out an independent air supply that, although it wasn't made for the dive market, has a lot to offer divers who want to travel light.

For years, helicopter pilots -- and some fixed-wing pilots -- have carried Spare Air cylinders on over-water flights. Weight is a critical factor on aircraft, and there just wasn't any other bailout bottle as compact and light. One significant disadvantage to Spare Air, however, is that you have to hold it in your hand to use it. It's a one-piece hoseless unit with a built-in mouthpiece. If you let go in the chaos of fighting to survive, you might never find it again. A new system from USD, the Micra Air System (MAS), lets pilots use both hands while breathing emergency air. It has some interesting advantages for scuba divers, too.

Versatile and Compact

The MAS includes a 2.5-cubicfoot cylinder; a two-stage regulator with a 24-inch hose; a nylon holster with a set of straps allowing easy mounting on a scuba tank, shoulder strap, or BC cummerbund; and a yoke adapter for filling the cylinder from a 3,000-psi scuba tank. It can also be purchased without the cylinder, equipped instead with an adapter that permits it to be threaded on any standard aluminum scuba tank.

The second stage is a brightyellow USD Micra, slightly detuned to reduce the likelihood of free flow. The firststage regulator is the most innovative feature of the system. The first stage and tank valve are combined into a very small, lightweight unit with a built-in shutoff mechanism. About the size of a standard tank valve alone, it can be screwed directly to any standard scuba tank by using an adapter. The mouthpiece of the Micra second stage can be clipped below the chin or on the shoulder for ready access wherever an octopus second would normally be worn.

I tested the system both with its own pony bottle and on a 6- cubic-foot Cliff Impact/Sherwood pony. The first stage innards are basically stock USD Conshelf (balanced diaphragm) parts, meaning that they can probably be found and serviced anywhere in the world. The entire system with the 2.5-cubic-foot pony is only 12.5 inches long and weighs about three pounds. That's well within my limits for carry-on air travel.

Pay Attention, Now

Filling the MAS is more trouble than filling a conventional pony bottle and a bit more inconvenient than filling a Spare Air. The excellent owner's manual breaks the procedure into 23 separate steps. A yoke adapter is used to fill, via a little plug on the side, whatever pony bottle you've attached to the first stage/valve. The plug has a tiny stem-type pressure gauge built into its face; a little dial gauge that displays actual tank pressure is also available. The whole process takes a couple of minutes, and you have to pay attention to what you're doing, but it's not as bad as it sounds.

Field Tests

I took an MAS on a two-week dive trip earlier this year and used it both with its own cylinder and with my own 6-cubic-foot pony. Because it's not as easy to crack as an ordinary tank valve on a regular pony -- a two-handed task, fairly difficult with wet hands -- I opened the MAS first stage/valve each time before jumping into the water. To prevent free flow, other ponies are often carried with their tank valves closed until needed.

It worked perfectly in all respects and was almost unnoticeable, fitting completely out of my way with its cylinder tucked behind my hip against my main tank, its hose under my right arm, and its second stage clipped to my right shoulder strap. The hose has a 360-degree swivel at the firststage end, making it easy to route without binding.

I packed both stages with grit, left them unwashed in the sun, banged them around on deck, and treated them as if they were rental gear. Not a free flow, not even a bubble in heavy current, and it breathed perfectly.

I had another standard Micra along, and the two felt essentially the same at depth. The Conshelf first stage is not a high-volume unit like the one normally shipped with Micra seconds -- and the Micra supplied with the MAS is set up for resistance to free flow, rather than optimum light breathing -- but it provided enough flow to supply me comfortably with plenty of air all the way down to my maximum test depth (about 150 feet).

The Bottom Line

The MAS's 2.5-cubic-foot pony isn't as large an independent air supply as most divers should carry, in my opinion, and is certainly too small to provide much security for deep dives. However, used on a larger pony, it's a very slick setup. It weighs less than a separate regulator and valve combination and is significantly smaller. For traveling divers hampered by airlines' size and weight restrictions, the MAS with its own pony is a good choice. Compared with Spare Air (the obvious competitive target), the MAS is more easily serviced in remote locations, is much easier-breathing, and leaves both hands free to deal with emergencies.

List price for the complete MAS is $599; street price is estimated at $400-$500.

The MAS without its own pony lists at $499; street price should be $325-$425. Note that this configuration does not include the pony bottle adapter kit (see below) but can be mated without any adapter to various special-threaded Cliff Impact ponies, such as the ones sold as part of the Spare Air. In other words, somebody with an old or unwanted Spare Air could use its bottle with the MAS without any additional adapter.

The MAS pony bottle adapter kit, which allows the MAS to be used with any standard tank valve, lists for $70 (estimated street price $58-$68).

The MAS is currently shipping only with the pin-type tank pressure gauge because USD still has quite a few of them in stock. When they're all gone, units will ship with the dial-type gauge instead. People who already have the pin gauge can order the dial gauge as an accessory. List is $60 (estimated street price $41-$50).

Delmar Mesa

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