A pressure pot is a small chamber that can be pressurized to test equipment in a convenient location, like home. If you are inclined to make equipment like camera housings, dive lights and such, or want to be sure that that light that has been hanging on a hook for the last year is water proof before that night dive, a pressure pot is a handy thing to have. Pressure pot designs abound. I made mine from an old aluminum tank, one made of the dubious 6531 alloy. Let me state that is my design. I am not an engineer, etc. I guarantee nothing, especially safety. A 6 inch diameter disk charged with 100 PSI has about a ton and a half of pressure on it. Plastic is brittle, threads can strip, bolts shear... If your head is over it peering in at the time...

Another important safety point is to fill the unit a much as possible with water, compressible air (read BANG) while necessary in this design, must be kept to an absolute minimum. You will see that my unit stands in a bucket so that I can fill it all the way and not worry about spillage.

What is the maximum test depth? My shop air compressor tops out at about 110 PSI which is in the 230 fsw range. Deep enough to test most anything that is going to be used on a recreational dive.

"Home made presure pot"

Light Lust is a disease that afflicts many divers. Those that dive deep, and or dark locations or who want to take pictures or video tend to be most afflicted. There is no cure for light lust, but for those with large amounts of cash, the symptoms can be minimized or at least controlled. For the rest of us it is either put up with an aching case of light envy or roll your own. I chose the latter road.

Canister lights are what you end up going to when the combination of light size and weight gets too heavy to carry comfortably in your hand. The batteries and electronics reside in a canister that attaches to your back plate or BC. The light head is attached to the canister with a cable and can be held, clipped to your hand, head, camera, etc..

The light I made is some what a throwback in that it uses a halogen lamp, not the newer HID or LED lamps. HID units are high voltage 600 to 1000 volts something I am not too fond of especially underwater. Their bulbs are expensive with limited life spans, there are other issues also. LEDs have evolved in the two years since I made my lights but they still have their quirks. If I make another light some time I will try an LED. The down side to halogen lights is that they tend not to be as energy efficient as the other two options. This means that you require a larger battery pack for the same illumination hours. Another issue is that the light tends to be yellower than HID and LED which affects color balance in photography and subjectively appears dimmer. My light supplies 16 volts to the 12 volt bulb. This has the effect of producing more light per watt and making the light whiter. This over driving to some extent offsets the disadvantages of the halogen bulb. The down side of over driving is that the bulbs burn out a lot faster. As the bulbs are readily available and cost about $5 this doesn't concern me too greatly. There are two hazards associated with over driving halogen bulbs. UV and heat. Just about all halogen bulbs produce some UV. The bulb is so bright that it is doubtful that anyone would be able to stare into it for very long and the glass in the lens and mask should provide some UV attenuation. Heat is another issue. An over driven bulb gets HOT! You risk damaging the unit if you run it out of water for more than a few seconds. More importantly, as the switch is touch sensitive, if the power is not disconnected before packing it is possible that the light could come on while being transported and start a fire. This is not your grandfathers flashlight!!

The light I made uses a standard 12 volt MR16 bulb. These are available in hardware and, home supply stores. Around $5. They come in a variety of wattages and beam angles. The reflector is built in and the filament is positioned exactly by the factory. Another nice thing about the MR16 is that is is an almost perfect drop-in replacement for the bulb and reflector in a standard Mag Light head. As the head is often the hardest thing to obtain when making a UW light, this is a very convenient arrangement.

The body of my light is made of Schedule 80 pipe and contains 14 NiMH.C. cells 3 grouped 4-4-4-2. It was a tight fit and accomplished only by removing the outer two wrappers on each cell. In the top of the housing resides a regulated power supply circuit (Light Geni . Australia) This circuit regulates the voltage to the bulb providing ¼, ½ and full power settings. As I am over driving the bulb, supplying 16 volts, the circuit also provides a ramp up feature to reduce the likely hood of the bulb blowing on start up due to thermal shock.

The mag light head was cut down to accept the bulb, a piezoelectric switch (waterproof and no moving parts) and the bulb socket. All the standard .o. rings were replaced with heavier ones and the plastic lens was replaced with a 1/8 inch borosilicate (Pyrex) one, due to the heat the bulb generates and the pressure it will be exposed to.

"Home made canister light"