Weird idea...POSITIVE pressure housing

Spending all my time designing pressure vessels, I can tell you that it is much, much, much easier to design for positive pressure rather than negative pressure. Vacuums can do horrible things, but that's what we subject our housings to everytime we go under. I'm pretty sure that our housings could be thinner (and lighter) but potentially more complex if they were designed to be positively pressurized prior to diving. The o-ring seal could be designed to accomodate this, however the deeper you went, the less it would seal due to the equalization of pressures.

In Cousteau's "The Silent World" there is a photo of a cine camera housing fitted with what I think he describes as a "mini Aqualung" - I'm sure he refers to this as a positive pressure housing in the text! This would date back to the late 1940s early 1950s. In those days they probably used sealing 'gaskets' as were used on the Rolleimarine housing, but today we have very well established and thoroughly tried and tested 'O' ring seals which actually work exceedingly well. As the last poster indicates, you would probably trade one Potential problem for another Potential probem which would need to be addressed. If you use and maintain them properly "O' rings are pretty reliable - I know of someone using a housing with a manufacturer's rating of 80m at 135m - that's not a bad margin.

Way back in 2000, on a trip to the Philippines, I'd seen this East German guy with a plexi box with a Nikon F camera in it. It had bathroom taps (seriously) to release the pressure. He wouldn't let me take a photo of it... well I did make one too many "which one is the hot water" jokes. He even had the same for his strobes... all connected together with pipes that acted as handles too.

He'd pump it up (ok I also made some Hans and Franz pump you up jokes) before every dive. The coolest homemade housing I'd ever seen.

Interesting.

 

Subal housings do not use suitcase clamps to pre-load the o-rings, they use a twist cam system.

 

The Hugyfot housing uses hex nuts to pre-load the o-ring. At depth the housing compresses these together and they can loosen. Something to watch out for before placing it in the rinse tank.

 

Cheers

James

I haven't experienced this problem, but then I have only been a Hugyfot-owner since November 2006. I can imagine it happening if you do not tighten the bolts enough. You should turn until the two halfs of the shell meets and you will feel a distinct stop. Then there's no room for further compression, hence no risk for the bolts to loosen. At least to me, this system feels very secure and confident.

/christian

... you would probably trade one Potential problem for another Potential probem which would need to be addressed...

However being a fan of gauges I would find this less of an issue.

Imagine that you would simply pump up your housing to the specified pressure required for the depth you seek.

The gauge on the housing would read the value and away you go.

The upshot here is that any leak would show up as a pressure drop or as bubbles in the H2O (instead of H20 in the housing) and one could simply head to the surface to increase the pressure much like the way ascending with an empty tank "magically" makes more air.

Apparently both Westinghouse and Sea Fathoms like the idea, they have issued US patents on how to do it.

BIll

The Fantasea Line housings all have stainless steel buckles.

Howard

Fantasea Line

This being the case with Fantasea its a good reason not to buy one. I'd never use a housing without some form of securing system for the back plate. Latches work fine if mounted & adjusted properly. Bolts may be more secure but are not user friendly. Releasing air from the housing while closing leaves equal pressure inside & out. (With a latching system the internal pressure may be slightly greater than external depending on design.) The only thing holding the back plate in place is friction (assuming a radial o-ring is used).

Right - I believe it's 10-Bar who uses the pressure locking system.

Cheers

James

...and I bet that they don't suffer from the rinse tank flood problem. It would be interesting to hear from some Hugyfot owners. I don't know much about them, since they are not that popular in the US.

I have a 40d in a Hugyfot housing. First Dive - First Flood. Thankfully it was just a small amount of water an the camera was fine. I'm not sure what happened, not problem on the test dive (empty) or dip tank. I have a couple of suspicions, 1) Eye Piece leaked (it had water in the partially sealed eye piece), 2) Under tightened the housing ( I followed the directions which said to stop when the bolts have significant resistance which is a bit subjective) and maybe the loosened when the housing was under pressure allowing water to enter was I ascended (the alarm occurred near the surface). 3) over greased the O-Ring or potential dust, didn't seem like that was the case when returned to the boat.

Hugyfot is making a Vacuum pump for their housing which I'll probably be one of the first users. It will allow you to test the seal at the surface and leave a small vacuum to aid holding the two halves together.

Should be interesting.

Yes, pressurising is a possible solution but the housing has to be designed that way first. For example look at what holds the dome in place on a standard Ike SLR housing. Wouldn't take much pressure on the surface to blow those two little black clips off - even if the O ring did seal.