Depth Limitations of housings

[Mark]

My F10 housing has a depth rating of 40m, it has been to 54m, without leaking or difficulty in operating the buttons. I want to take mine deeper.

Does anybody know why they are restricted to 40m? Is it due to the limitations of the seals? Or the fact that the pressure will force the buttons down and operate all the buttons at once?

If it is a matter of the buttons being forced, would uprating the springs cure this for deeper dives? Say down to 100m, I realise that it would make it difficult to use in the shallows.

If it is a matter of the seals not taking the pressure variance, is there available, of has anyone tried some sort of pressure equalisation system, i.e. a mini reg with a CO2 canister & over pressure valve, this would also cure the button problems too.

I havent seen anything like this available, but it might be lurking out there somewhere.

[Mike W]

I think you've got most of the reasons, but you'd also have to consider the pressure on the relatively thin walls of the housing itself. At real depth this would distort the housing body so it couldn't seal, even if none of the O rings gave, and could even squeeze it so much that the camera lens would touch the front port.

The thicker acrylic housings from Ikelite carry a 60m rating, and there are 90 and 100m rated housings for SLRs, generally made in metal, and the Nikonos range were metal bodied and 'conservatively' rated to 50m.

Adding positive internal pressure sounds like a solution to me, but I'm not aware of anything like that, though I'd be willing to bet someone out there has tried it!

Oh, and you're braver than me, my 40m rated housing has been to 47m, but I chickened out there!

[Cussy]

Bonica analogue cameras have a blow up adaptor, point is you can test its sealed at the surface. Some seals may be designed to work with the higher pressure on one side only. You may find that internal pressure wont hold. At work we go to pressures equivilent to about 10km depth and all our pressure vessels have to be tested to 1.5 times or 2 times working pressure. So you might find a 40m housing could go to 80m for short periods - DON'T QUOTE ME ON THAT!!!
Rob

[KenByrne]

I'm sure you're right that the housings are engineered to withstand more than their rated depth. It's a bit like watches where a 50 metre rated watch is ok for washing the dishes. I believe that's because of the difference in static and dynamic pressure. But I'm also sure that it's to build in a safety margin. Problem with taking your camera beyond it's rated depth is you'll only know you've gone too deep when it's too late.

[Mark]

I want that INON adaptor, I'll see cameras underwater at LIDS I think.

My idea about equalising the pressure would be some sort of pressure balancing valve, similar to a 1st stage reg, except being set at 10bar above ambient, set at 0.1bar , fed by a small CO2 cylinder like a sparklets one. Then for the ascent an overpressure valve.

You could always do the same thing with a balloon, connected to the housing, as the pressure rises the balloon would crush to equal the ambient pressure within the balloon and housing. The only depth restriction would be the size of your balloon.

I think I've got it.

If you used your drysuit/wing/BCD as a balloon, with a small pipe connected to your housing, your drysuit would balance the pressure instead. Problem solved. I am going to buy a cheap 10m camera and modify it to see how well that will work.

Any comments.

[johnny boy]

I think the ratings of a housing has a lot to do with the manufacturer being conservative.* i.e.* 40m rating is probably well within what it will actually do maybe.* I once had my olympus PT020 pressure tested to approx 50m and it held up fine even with the flash bulkhead replaced with matthias Heinrichs adpater fitted my me!* I also think it's the maufacturers way of also saying - dont dive beyond 40m!* They must have a pact with PADI!

[bubblemaker]

Originally Posted by johnny boy

I think the ratings of a housing has a lot to do with the manufacturer being conservative.* i.e.* 40m rating is probably well within what it will actually do maybe.* I once had my olympus PT020 pressure tested to approx 50m and it held up fine even with the flash bulkhead replaced with matthias Heinrichs adpater fitted my me!* I also think it's the maufacturers way of also saying - dont dive beyond 40m!* They must have a pact with PADI!

I would make a guess that the depth ratings on housing are a similar thoery to that of sell by dates on food (i used to work in a supermarket) they are there as a guarantee. food is generally still eateable quite a while after the sell by date, and i guess it's the same with housings...

that is to say, assuming it is properly mantianed, a housing rated to 40m, could quite probably survive down to 50-60m, and the 40m rating is only a guarantee that it will perform at that depth.

though if you are going to test this theory i would suggest not having your camera in it a few times... just to make sure!!