Weird idea...POSITIVE pressure housing

OK, so from a really basic physics standpoint, camera housings are closed at the surface, containing sea-level air pressure, so when you descend the interior is actually at a relative vacuum. The pressure on the outside is hopefully channeled in effect by the housing design to help push the 'halves' of the housing together against the o-ring and thus aid the seal. Buttons need springs though to keep from being 'depressed' by the exterior pressure differential, which is why housings have a max depth rating. (Well, also implosion of the case itself, but that's I imagine secondary to losing the ability for the buttons to 'unpress'.

The internal relative vacuum means that when the seal does break, water's going to be actually 'sucked' in, however.

So I got to wondering....has anyone ever tried positive pressure cases? Seal it up, pump it up with some sort of pump arrangement through a valve that can be sealed off (maybe a CO2 canister, maybe a bicycle pump of some kind) to a positive differential relative to sea level to the intended dive depth, and then dive? The interior to exterior differential can still help hold a seal shut, and I know it's easier to design something that can withstand negative internal pressure than positive internal (or is it - scuba tanks do it just fine). But then if you always 'overpressured' a bit relative to your intended dive depth, while underwater a seal leak would just vent bubbles and give you plenty of warning to start ascending.

I know, logistically having to inflate your camera housing sounds kind of iffy (extra power inflator connection? ) but I was just messing around with bottle rockets and the thought came to me.

Let the scoffing begin!!!

I came across a Japanese camera guy who had made a kind of dry suit bag for his full size BETA Sony camera.

He put the camera in, zipped up the bag, plugged in a LPH to it like a dry suit and away he went.

On a dive trip to Bora Bora in 1997, I ran into a fellow who did this. He had drilled a hole into his video housing and glued in a bicycle valve. He then pumped up the housing before each dive with a bicycle pump to 30 psi. His argument was that if there was a leak, you could see the bubbles coming out of the housing and then could ascend before damage was done. It seemed to work, but I was a bit concerned that at 30 ft the exterior pressure would match the interior pressure and the o-rings would shift in their grooves.

By the way, the whole concept that the water pressure is needed to push the halves of the housing together to 'improve" the seal is true only because the traditional housing o-ring design is undercompressed by the suitcase clamps that used to close the housing. If the o-ring groove was designed using standard mechanical engineering textbook designs, it would require screws to compress it, but it would be good to 1000psi and would never leak in the rinse tank. As far as I can tell, the housings were originally designed in the film days when you needed to pop them open after every dive to change film, in which case the suitcase clamps were very convenient. Nowadays, I close my housing in the morning and open it in the evening. I would gladly trade the suitcase clamp design for something that was more robust and didn't have a penchant for flooding in the rinse tank, even if it meant more time to assemble and teardown.

You could use a hydraulic pressure compensated seachest - It would work but wouldn't be pretty.

James

Hi!

I wouldn't do it at all. The cameras are not designed for much higher pressure than ambient air pressure at sea level. Some manufacturers have a note on this explicitely written in the manual.

Some of the parts inside may not withstand the pressure in the first place or trap gas and explode when lowering the pressure during ascent or opening the housing.

There have been reports on damaged DSLRs used in ewamarine bags where the camera is exposed to water pressure during the dive.

It wasn't so much problem with mechanical analog cameras but could lead to image sensor destruction or other serious damage in a digital camera.

There are other ways to avoid stuck buttons. One is to use no buttons at all but use gears. This way you de-couple the surface pressure inside the housing from the water pressure outside.

The mechanical solution isn't cheap but it works great (in most of the housings the shutter release is built this way). Another option would be an electronic remote control. The problem is that DSLRs need custom connectors and controllers to do this, for video there's a standard so there's a general solution (less development efforts).

In general, I think that the common push-button design allows proper operation down to 60m which should be sufficient for non-technical scuba diving. If you want to go deeper it will get expensive anyway and a custom housing won't be the crucial financial factor.

Helge ;-)=)

Saw a presentation where they discussed just such a housing for the IMAX camera that Howard Hall used...

Its already been done, long before "buttoms" were a problem.

Photos show installation on a Nikonos V, (also made for the RS) Ikelite housing and the pump.

Phil Rudin

Phil,

Doesn't the subalert pull a vacuum inside the housing? Similar concept, but the opposite :-)

Cheers

James

Hi James,

I'm sure your right. I always looked at this as just somthing else to go wrong so I never spent all that much time researching it.

Phil

If you look at old Cousteau films/pictures you will see that the pressurized housing is a concept that has been around for a long time, probably before JYC used it.

One thing I can live without though is another low pressure hose on my regulator.

M

Saw a presentation where they discussed just such a housing for the IMAX camera that Howard Hall used...

The IMAX housing is actually a vacuum fitting, not a positive pressure housing if I recall correctly. Howard Hall actually has a similar fitting on his other camera housings also to insure a good seal.

Vacuum is good because it precompresses the o-rings in the RIGHT direction. If you overpressure the housing, you could blow the o-rings out - something you don't want to do :-)

James

Vacuum is good because it precompresses the o-rings in the RIGHT direction. If you overpressure the housing, you could blow the o-rings out - something you don't want to do :-)

 

James

True, but with appropriate design of the o-ring containment, that also can be taken into account. You wouldn't design a groove/o-ring that is supposed to support negative pressure the same way you design one that's suppose to hold against positive pressure. (or you do, but the inside and outside references are swapped )

Thanks for the discussion folks. It was just an idle thought, I'm glad it got some airtime.

By the way, the whole concept that the water pressure is needed to push the halves of the housing together to 'improve" the seal is true only because the traditional housing o-ring design is undercompressed by the suitcase clamps that used to close the housing. If the o-ring groove was designed using standard mechanical engineering textbook designs, it would require screws to compress it, but it would be good to 1000psi and would never leak in the rinse tank. As far as I can tell, the housings were originally designed in the film days when you needed to pop them open after every dive to change film, in which case the suitcase clamps were very convenient. Nowadays, I close my housing in the morning and open it in the evening. I would gladly trade the suitcase clamp design for something that was more robust and didn't have a penchant for flooding in the rinse tank, even if it meant more time to assemble and teardown.

IIRC, Hugyfot is the only housing mfg that does not use the suitcase clamps but instead the hex head bolts to close their housings.

From the Fantasea Line manual. The DSLR housings and land strobe housings rely on air released from the housing while the rear cover is being pushed into place to hold the housing closed, it has no locking devise.

"Close Housing

1. Place housing back over front and align the complete mating surface of the housing and

the gasket, forming a proper seal.

2. Ensure that the pressure release plug is pulled all the way out while closing, otherwise the

air cannot escape.

3. Squeeze the lid closed all the way, you will hear the hiss of air being expelled.

4. Screw home the pressure release plug; you need not excessively tighten this plug. The

seal is made by the internal O-rings. The O-ring on the underside of the plug is just to

keep out dirt and other debris".

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).

IIRC, Hugyfot is the only housing mfg that does not use the suitcase clamps but instead the hex head bolts to close their housings.

...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 saw these on some ikelite housings at one of the places i worked at.

It was like a low pressure valve that you get on your bcd .. and you could pump them up like your bcd !

It had a pressure regulator on it .. i think. hard to remember i only saw it once about 7 years ago.

but i was told these were made because ikelite housings had a bad habit back in the day of flooding and so you could fit these yourselves and pressurise your housing .. the physics of which would lower the risk of flooding as you no longer had to wait for the water to create pressure on the housing to seal it as it would be sealed on the surface and youcould put it in a tank of water .. if air came out you had a leak but no water would get in before you dived type of thing.

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

The IMAX housing is actually a vacuum fitting, not a positive pressure housing if I recall correctly. Howard Hall actually has a similar fitting on his other camera housings also to insure a good seal.

there was also a case where they used a splash housing, though. The housing wasn't meant to be submerged, so they pressurized it so it could be submerged.

The added pressure did make some of the film handling mechanisms act up.

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