If you plan shooting near the maximum depth ratings (of domes), using a vacuum valve system has its benefits and drawbacks.
A vacuum valve will improve O ring sealing on the surface and very shallow waters (less than deco depths). It also will help you to avoid some common user mistakes and might provide some "peace of mind".
However, for maximum depths, the partial vacuum (0.2-0.5 bars) will increase the pressure differential and consequently decrease the nominal maximum depth by as much. In other words, the dome might implode 6-15 feet shallower than it otherwise would. Secondly, the valve is yet another protrusion on your housing and thus slightly increases risk of line entanglement etc. Additionally, the valve itself is an additional leak point. If you do not close the valve fully, it might be airtight at the surface, but still leak at maximum depths. Finally, should your vacuum circuit alarm whilst at bottom, apart from turning the housing to face downwards, there is not much what you can do until returning to surface. With one or multiple hour deco obligations you can only listen to the continuous alarm and watch as the dome fills with water. Sending the camera with a SMB to surface has its own risks, multiple risks.
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