For those of us who don’t own one of these housings, the only solution was, and still is, a third-party system.
Some models have appeared from across the Atlantic and have already featured on these pages. Meanwhile I have been using and evaluating for the past year a system from Europe – the Leak Sentinel from Slovenia-based Vivid Housings.

The Principle
Simply put, a negative pressure is created inside the closed and (we hope) sealed camera housing by removing a small percentage of the air. The housing is left to sit for a short period of time, during which any leaks will result in air being drawn in from the outside, equalising the pressure inside......

There are a couple of ways to indicate equalisation of the pressure. An analogue
gauge can be fitted and used to indicate a drop, or it can be monitored via electronic wizardry with a permanent visual display showing the state of play.
Air, unlike salt water, is non-destructive, so if you have a leak it won’t destroy your expensive camera system and ruin your week.
Air is also less dense than water, and will find even the smallest inlet caused by hair, fluff, grit or salt crystals on the housing’s O-rings or mating surfaces.

The Design
Version 3 of the Sentinel features a calibrated pressure-sensor and processor in the form of electronic circuitry that’s set in a robust anodised aluminium body. Tiny red or green LEDs behind a transparent acrylic window indicate the pressure state inside the housing.
A one-way valve is formed by a red silicon disk, which is in turn sealed via a screw-in blank cap. Vivid supplies various stainless-steel adaptors to connect the whole thing to the camera housing via an unused bulkhead port. Every joint is O-ring protected.
Power is supplied from a coin battery fitted inside, making the whole unit self-contained and compact.
I fitted the Leak Sentinel to my Subal Nikon D800 housing, which has three 14mm bulkhead ports, two of which I’ve used for Nikonos-type three-pin strobe synch connections and the third (which was originally a spare and blanked off) for the Sentinel.
Vivid supplied my unit complete with a stainless steel M14x1 adaptor, which fitted seamlessly into the Subal with an O-ring seal.
I had to juggle the bulkhead connections a little, as the original layout put two ports close together. The Leak Sentinel is 31mm in diameter, and there wasn’t room to connect the Sea & Sea synch cable when it was fitted.
Instead I positioned it on the right-hand side, just above the housing’s shutter release, and placed both the strobe connections on the left.

In Use
Before activating the Leak Sentinel, all the O-rings, grooves and mating faces need to be checked for any contamination and the housing’s rear clamshell securely fastened.
The Sentinel is switched on by removing the blank cap and pressing firmly on the centre of the silicon valve-seal, which activates a micro-switch. The unit automatically and instantly calibrates for the ambient air pressure.
A red flashing LED will be seen through the transparent acrylic window at this stage. Screwing the pump adaptor into the threaded valve body connects the hand-pump, and by pumping slowly air is extracted from inside the housing.
The number of strokes varies, depending on the volume of the housing and the choice of port. With a 60mm macro port fitted, around six or seven strokes starts the LED blinking alternately red and green. A further five or six and the LED shows only green, indicating that a sufficient negative pressure has been achieved.
It’s a case of waiting with your fingers crossed for 15-30 minutes to see if the LED changes back to flashing red, which would indicate an equalisation in pressure and therefore a leak.
If this is the case, the integrity of the housing will need to be re-checked and the process repeated until a satisfactory seal is achieved.
I like to leave the unit switched on for the whole diving day, and have found that it lasts for at least a fortnight of use. After the dives, the protective blank cap can be removed and the pressure equalised with a simple sideways movement of the silicon seal. A firm press to its centre then turns the unit off.
I’ve heard horror stories involving dome-ports coming adrift when a camera-housing has been passed to a diver on the surface, but the vacuum system clamps everything tightly in place, including the lens ports, making it almost impossible to remove them.
I’m not a boffin, I’m a diver, but I do know
that as a gas (air) increases or decreases in temperature the pressure also increases or decreases. It would therefore be feasible that if you set the Sentinel up in an air-conditioned room and then took it out on the hot, sunny deck of your dive-boat, the pressure would rise inside the housing and falsely indicate a leak.
Well, in the 12 months that I’ve had this unit fitted this situation has not arisen – and it has been used almost exclusively in hot climates.
The opposite would happen if you took the camera-housing from a nice warm environment and then dived in the cold winter waters off our coastline, although this would have a positive effect as the internal air volume was reduced.

Unlike some models of vacuum leak-detectors, the Sentinel’s integral LED indicators offer instant feedback without having to fit a gauge to see if the pressure inside has dropped.
For me this represents a real-world advantage, because a quick glance is all that’s needed to make that all-important decision about whether to take the camera under water or leave it at the surface.
The Vivid Leak Sentinel needs an auxiliary port to be fitted to an underwater camera housing, and unfortunately these are not found on most compact models. However, if you own
a housing that has one, Vivid can supply an adaptor to retrofit the Sentinel.
After a year of hard diving representing almost 300 hours under water, my Leak Sentinel has proved robust and reliable.
Most significantly, there have been a number of occasions on which I’ve found that the housing wasn’t sealed properly, and the little Vivid system has saved the day (and my wallet).
It has become an integral part of my photographic set-up – one I wouldn’t ever want to be without.

PRICES 200 euros, free shipping to the UK
SIZE 25 x 31mm diameter
WEIGHT Valve body 45g, Hand-pump 140g
POWER 3V CR1632 lithium coin cell battery
ADAPTORS Sea & Sea, Aquatica, Nauticam, Subal, Hugyfot, Seacam, Ikelite
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