Airspeed Press Gallery

These are pictures that didn't make it into the book, or haven't yet but will at the next revision, or just ones from the books that we thought you poor benighted souls who haven't bought any of our books might find interesting. We will be adding more from time to time. Back to Airspeed Press Main Page



In the DIVELIGHT COMPANION Steve tells how to build a pressure pot for testing lights out of an old aluminum 80. He also says that while he used a piece of 20 year old 1/2" acrylic for the top, he felt was really too thin for the application, and cautions such a pot should only be used completely filled with water (to eliminate explosive potential should it let go), and not to put one's head in line with the top while it is pressurized just in case it decides to let go.

Good advice all, it turns out. Shortly after pressurizing it Steve heard a dull pop. The gauge/filler fittings leapt about a foot in the air and the cover split into four wonderfully equal sections.

As explosions go it wasn't very spectacular, and wouldn't have done any harm even if he'd been staring straight down on it. But its a good reminder that redundant safety precautions are always worth taking when using homemade gear. It's also a good reminder that cycles add up when you are dealing with pressurized gear - the pot had made previously made several hundred runs to as deep as 250' without trouble.

The pot is getting a new cover made of 3/4" acrylic, and the gauge/filler fitting is being located off to the side where it won't act as a stress concentrator. The tapered NPT fitting will be replaced with a straight thread O-ring sealed one as Steve suspects stress induced retightening the tapered fitting was a major contributor to the failure.

However. with big 14Ah canisters going the way of the dinosaur such a large pot is rarely necessary anymore, making some much simpler alternatives possible. Steve's got a new smaller pot - a stainless steel Hudson Industro sprayer he bought home from the dump. It's got a big 3-1/2" cleanout door that snaps on and off in seconds. A built-in hand pump allows it to be pressurized quickly without having to fire up the compressor. The only drawback is that the pump is good only for 80 psi (180') or so, but that's plenty for casual testing.
On the left is a "Cornelius keg" originally holding soda syrup from an earlier dump visit. Made of heavy stainless steel with a 3-1/8"x 4" oval door, and rated for 130 psi they also make great pressure pots. Frequently found surplus/scrap now that they are being phased out by the soda industry, they can be had on eBay or from homebrew beer suppliers for $12 - 30.


  Oxy-safe lube is too expensive to waste wiping your fingers on your jeans. Make your own 'lubritorium' by putting just a dab of it in a small zip-loc bag. To use, drop the O-rings in the bag, work them around a bit, and squeeze them out, perfectly lubed with no waste.
  OXY HACKER analyzer built into a Pelican watertight box. A simple "L" shaped panel is attached to the box by two plastic standoffs which are epoxied to the bottom of the case, and drilled at the top to accept the mounting screws. The analyzer only takes up half the box so there's plenty of room for accessories and odd bits.
  Compact samplers, a BC QR and a hose barb version. The $6 BC version incorporates a flow reducer (made by simply plugging the bore with a less-than-perfectly-tight threaded plug), making a very economical and compact one-piece unit. The hose barb version is set up for use with a regulator and flowmeter. It would be possible to build either version into the boxed analyzer shown above, simply by drilling a hole in the panel and mounting the hose fitting on one side and the chamber on the other.


The new OXY HACKER continuous mixer. This nifty gadget pumps nitrox at the same time as you are filling a tank. Since the O2 is added at ambient pressure, before the air is compressed, the tank and mixing setup never see 100% O2. The risks of transfilling HP O2 are completely eliminated and O2 clean tanks are not needed. The only catch is, you need a compressor, but it works so slick it's almost worth buying one just for the mixer.
You can buy a commercial continuous mixer for $800-2000 - or build ours for about $25, and buy the compressor with the money you save!




Hyper Filters - filters for super-cleaning air that will be used in partial pressure nitrox mixing - are expensive, at $800-$2000.

The one shown here (and just visible to the left of the compressor in the previous photo) was made from an ex-Airforce hydraulic accumulator, bought surplus for $30. A spring loaded endplate is absolutely essential in any filter stack, to prevent the media from settling and allowing the air to channel through.




Using two slightly different surplus accumulators, Bob Fridell built this gorgeous portable hyperfilter/mixpanel into a Pelican box.

The little stubs are male QRs for hooking up the hoses.



An inside view of Bob's filter/panel, for all you Swagelok/Nupro junkies.

The first canister holds driers, 20% silica gel and 80% 13X, and the second one 50/50 LPC (low purity carbon) and HPC (high purity carbon), making for true hyper filtration.



Another approach to a low-cost hyperfilter: find some appropriate thick-walled surplus or scrap SS tubing, and make O-ring sealed end plugs that are held in with cross bolts, thus avoiding any complicated machining or threading.

This only works with lower pressures and smaller pipe sizes, as the pressure on the bolts can otherwise quickly become more than they can handle.

  Cale's Swiss Army Knife. An old SCUBA regulator 1st stage fitted with a $5 surplus flowmeter. Why? It makes a great sampler, for analyzing nitrox, or tank pressure checker, and also can be used for emergency O2 administration, to allow running a constant flow non-rebreather medical mask off a SCUBA cylinder filled with O2 such as a deco bottle.


While our DIVELIGHT COMPANION has plans for building heavy duty "pro" canisters just like the ones you can buy, some people just want to get in the water fast so we've included plans for some easy to build "Instant Divelights".

The canister shown can be made in an hour or two from hardware store fittings, to fit lead acid or NiHMs, for as little as $35 including the battery. It'll power a commercial or homebuilt halogen or HID lighthead - and has been tested to 200'!



Halcyon Helios NiHM canister lights using "Fat A" 4500 mAh cells. The Halcyon canisters are machined from a single slug of Delrin, but similar canisters can be easily homemade from PVC pipe.


The battery packs use a 7-7-6 and 4-4-2 cell layout, to give 9Ah and 4.5Ah at 12V.

  Close-up of a typical NiMH canister, with a squared-off switch guard (to fit on the tiny top) and locking compression catches.
  One "instant divelight" trick from our divelight book is using an $18 Mag-Lite flashlight as a no-machining lighthead - the Mag-Lite has O-ring seals throughout, and a 50W halogen MR16 reflector bulb fits in as if it were made for it.
Only problem is, the handle is a bit on the long side, and it's hard to seal off the switch hole.
Marshall Reymard and his buddies in the South Shore Neptunes came up with a neat refinement - make a Delrin stub to replace the handle. It takes a little lathe work, but it's still a lot easier -and cheaper - than making a lighthead from scratch.



While we were playing with Mag-Lites, we couldn't help but notice that the 10W HID ballast is a perfect fit in the D-cell Mag-Lite tube. The tube must be cut down, to eliminate the switch, and can be either remachined to fit the head or simply cemented in place using a waterproof epoxy or urethane.

This one uses the reflector from an MR16 bulb. The beam can be adjusted on the surface, by using spacers to adjust the relationship of the bulb to the reflector. And it just might also be possible to make a UW-focusable version, using the range of adjustment in the standard Mag-Lite head.

This is very much a work in progress, and anyone who choses to emulate it does at his or her own risk.

The new 4th Edition of the OXY HACKER has a neat formula for calculated flow at a given pressure through an orifice. Since owners of some of the previous editions have requested a copy we're posting it here.