Sealife 3.0?

[jonhall]

Whatever internal pressure it has at the surface will increase as depth increases. The external pressure will act upon the enclosure, seeking to compress its walls and especially squeezing the door tighter into its seal. The resulting reduction of volume must yield an increase of internal pressure. It may still be negative relative to the surrounding pressure, but the increase will definitely occur.

Was just typing a response to this as your post came through. Agree with this 100%.

The phone also has spaces with air. Pressurizing the inside of the housing could increase the air pressure in some of these spaces - when going to a depth, and because the housing could be considered a flexible container (I believe) because of the o ring, the pressure will increase inside and outside of the phone itself. Maybe they were considering possible damage??

 

[jonhall]

BTW, there are some great photos taken by @Trailboss123 with his Sport Diver housing and iPhone in a trip report he shared awhile back: Trip Report - Cozumel- October 10-20, 2021

 

[TNEngineer]

The phone also has spaces with air. Pressurizing the inside of the housing could increase the air pressure in some of these spaces - when going to a depth, and because the housing could be considered a flexible container (I believe) because of the o ring, the pressure will increase inside and outside of the phone itself. Maybe they were considering possible damage??

True, but with the phone in a sealed case the change of pressure the phone would experience would be modest. The seal will compress, and the (plastic?) walls will go concave slightly, but the percentage of volume reduction would still be very small and the resulting increase in pressure likewise small.

Open volumes in the phone won't matter as they will always equalize with ambient. I seriously doubt there are any closed volumes that cannot take the modest pressure increase caused by a compression of a sealed case at any typical recreational diving depth. Exposed to the depths without a case, on the other hand....

 

[Pipehorse]

Good point about pressurization reducing the o-ring seal.

However, I wouldn't say the enclosure is at a relative vacuum at depth. Whatever internal pressure it has at the surface will increase as depth increases. The external pressure will act upon the enclosure, seeking to compress its walls and especially squeezing the door tighter into its seal. The resulting reduction of volume must yield an increase of internal pressure. It may still be negative relative to the surrounding pressure, but the increase will definitely occur.

This leads us to the question of whether it's better to have positive, negative, or ambient pressure at the surface. I'm going to revise my earlier position and say I'd prefer ambient. Positive pressure is bad because it reduces the reliability of the seal. Negative is bad because it "encourages" water intrusion. That leaves us with neutral pressure, which at the surface has no effect (good). At depth the internal pressure will always be lower than the external - theoretically a bad thing - but having the differential in that direction encourages better sealing which works in our favor. And a pressure sensor could still provide early warning of a leak, at least a sudden one, by watching the slope of the curve.

In practice a normal housing always has a slight positive pressure because the seal first makes contact, and then gets compressed a bit by whatever latching system is used. Unless you provide a bleed port - itself a potential point of failure - there's no way to avoid this. So if I were designing it, I'd just do "the usual thing" and provide a seal and a latch, with no vacuum or pressure pump at all.

So I get your point that a certain amount of flex in the camera housing (especially the door) will decrease volume slightly, thusly increasing pressure, but this should be negligible (the polycarbonate used on the door of the ikelite housings I have is 11/16 thick). When I say relative vacuum, it means less pressure. Not trying to be semantic, but when I pressurize my scuba tank couldn't ambient air pressure be considered a vacuum to the tank? Regardless, then perhaps the best pressure system for a camera housing would be one that maintains the pressure in the housing equal to the ambient pressure at depth. Similar to how regulators allow our lungs to be equal to ambient pressure at depth.

 

[jonhall]

I seriously doubt there are any closed volumes that cannot take the modest pressure increase caused by a compression of a sealed case at any typical recreational diving depth.

I thought that also until I realized, recently, that the iPhones have sensors for barometric pressure.

This scenario reminded me of taking a juice bottle half filled with water and hitting the opening with a rubber hammer, compressing the air against the water, in turn pushing on the bottom of the bottle causing the bottom to blow out.

 

[TNEngineer]

So I get your point that a certain amount of flex in the camera housing (especially the door) will decrease volume slightly, thusly increasing pressure, but this should be negligible (the polycarbonate used on the door of the ikelite housings I have is 11/16 thick).

Agreed, the effect will be small. The important point is the internal pressure will remain neutral or increase. It will not decrease at depth, as was suggested earlier in this thread.

When I say relative vacuum, it means less pressure. Not trying to be semantic, but when I pressurize my scuba tank couldn't ambient air pressure be considered a vacuum to the tank?

Agreed again. This is why I said "I wouldn't say the enclosure is at a relative vacuum at depth" earlier. Vacuum is a misleading term in this context. We're talking about relative pressures.

Regardless, then perhaps the best pressure system for a camera housing would be one that maintains the pressure in the housing equal to the ambient pressure at depth. Similar to how regulators allow our lungs to be equal to ambient pressure at depth.

I must disagree here. Regulators increase the pressure of the available air because our diaphragms would not otherwise be able to overcome the ambient pressure and inflate our lungs. But electronics are not like that. Recall the above discussion about trapped air cavities... if you increased the case's internal pressure to ambient at depth, any trapped air cavities would then be subjected to the full pressure differential. Leave your ears unequalized if you want to know what that would be like! {grin}

I don't have any data on the pressure resilience of all the components in any given phone. But I can tell you that typical IC packages (non-COB mounting) often have voids in the leadframe/wirebonding area. I suspect those packages are not designed to take multiple atmospheres of external pressure. Most humans don't encounter ambient pressures anywhere close to what we experience at even modest diving depths. At 66 feet we are at 40+ PSI. I bet cellphone manufacturers don't increase the cost of their products to tolerate pressure extremes because few consumers are going to benefit.

EDIT: Guinness reports the highest barometric pressure ever recorded was 1083.8mB, which is just 15.8 PSI. Even if they allowed themselves some margin above Guinness, say a whopping 20 PSI, that pales in comparison to what a cellphone would experience at depth in an "equalized" case.

 

[Pipehorse]

I don't have any data on the pressure resilience of all the components in any given phone. But I can tell you that typical IC packages (non-COB mounting) often have voids in the leadframe/wirebonding area. I suspect those packages are not designed to take multiple atmospheres of external pressure. Most humans don't encounter ambient pressures anywhere close to what we experience at even modest diving depths. At 66 feet we are at 40+ PSI. I bet cellphone manufacturers don't increase the cost of their products to tolerate pressure extremes because few consumers are going to benefit.

Right, I guess it would be the case for cameras as well, consumer electronics are not engineered for pressures greater than ambient atmospheric, whether it be iphones or cameras. I was more opining at keeping the pressure the same in the housing as ambient pressure at depth as a good way to keep water intrusion to a minimum in case of a bad seal, knowing full well it would be impractical to do so. I realize the regulator lung analogy is not the greatest, drysuit inflation to prevent squeeze is a better analogy, though of course impractical again because of the electronics unable to sustain the greater pressure and the ridiculous rig that would result trying to keep the housing equalized.