New Housing "Airlock" Vacuum from Backscatter

perhaps some one with scientific background could comment on this. Is there a difference between pressure applied to the exterior and seals of a housing by air or water? My uneducated guess is that there is no difference. However, given water is much denser than air would this density difference be an influential factor?

To current users of these systems; how do you prevent aspirating a few drops of water when you bleed off the vacuum to open the housing?

So how do these systems prevent the aspiration of salt water being sucked into the housing when they are bleed to allow the housing to be opened??????

I can see how this aspiration is prevented with the Hugyfot, but how about the Backscatter and the Housing Sentry systems????

perhaps some one with scientific background could comment on this. Is there a difference between pressure applied to the exterior and seals of a housing by air or water? My uneducated guess is that there is no difference. However, given water is much denser than air would this density difference be an influential factor?

Why should there be a difference with pressure for Seawater?

/Erik

perhaps some one with scientific background could comment on this. Is there a difference between pressure applied to the exterior and seals of a housing by air or water? My uneducated guess is that there is no difference. However, given water is much denser than air would this density difference be an influential factor?

The housing has no way of knowing if the pressure inside is 0 psi, vs 15 psi outside, or 300 psi inside vs 315 psi outside. It only responds to the pressure differential between the inside and outside.

However, water is more viscous than air, and it has a higher surface tension, so I would expect a given size of leak to leak much faster for air than for water. So, if anything, the vacuum systems are conservative.

The main difference is of course that the biggest pressure differential you can produce with a vacuum is atmospheric pressure, about 14 psi. This is equivalent to roughly 33 feet of depth in salt water, and that is only if you manage to pull a near perfect vacuum. So if you go to 60 feet, then the housing is seeing a bigger pressure differential than you tested it to with the vacuum. I guess the housing or the o rings could deform a bit more and so something that doesn't leak at 30' might leak at 60'. I'm not saying this will happen, but I can see how it might be possible.

Still, my understanding is that most floods are because of damaged or non-existant o-rings, or because there is crud on the o-ring. I suspect that while a vacuum system might not prevent 100% of floods, it would probably prevent the majority of them.

Hugyfot recommends at least a 20 minute interval between getting the green light and entering the water so it accounts for the slowest of leaks.

@John: What does Hugyfot recommend in the other direction, ie time from diving until opening the Housing? Do they have a recommendation?

Still, my understanding is that most floods are because of damaged or non-existant o-rings, or because there is crud on the o-ring. I suspect that while a vacuum system might not prevent 100% of floods, it would probably prevent the majority of them.

A electronic vacuum system will not prevent 100% of floodings, but it will inform you 100% if the house is not sealed properly.

@John: What does Hugyfot recommend in the other direction, ie time from diving until opening the Housing? Do they have a recommendation?

Hugyfot gives no recommendation how long to wait until opening the housing,

but common sense will recommend to dry it well before you open it.

Chris

Why should there be a difference with pressure for Seawater?

 

/Erik

I don't know but the question was asked.

However, water is more viscous than air, and it has a higher surface tension, so I would expect a given size of leak to leak much faster for air than for water. So, if anything, the vacuum systems are conservative.

That's articulates the question and answer perfectly.

Thanks for showing the Huyfot valve. Now I understand why John Bantin is able to use the vacuvin and I couldn't for the life of me figure out how to use it on my system. Completely different sized valves.

John Bantin is able to use the vacuvin

Here is what was said about it : http://wetpixel.com/forums/index.php?showtopic=48364

I have a Hugyfot housing for Canon 400D and I am getting more and more interested into this topic !

Thanks for showing the Huyfot valve. Now I understand why John Bantin is able to use the vacuvin and I couldn't for the life of me figure out how to use it on my system. Completely different sized valves.

Andy

The vacuum fitting on the Housing Sentry is a spring loaded check valve. It will not open to flow vacuum unless you have the input fitting installed. When you install the input fitting it opens the valve for flow. If you want the use the wine bottle pump you will have to figure out how to adapt it to fit the input fitting.

Just found this thread and pleased to see that for once I'm ahead of the pack. I just fitted and used on a trip to the Northern Red Sea, a Housing Sentry from Bill Libecap. This is a two part electronic version, Bill kindly tailored a valve assembly for me to fit in the threaded housing hole of my Ikelite D300s housing. Now I know that Ikelite are not the most ergonomic housings, I try to set the camera up as far as possible and not alter settings underwater, and so I seldom if ever use the control for DOF and the F button on the D300s also the push rod used for those controls is the single thing making camera installation difficult so it was obvious to me that sacrificing this control was a minimum risk installation strategy. It took about an hour to install worked first time and has given a huge increase in confidence in use after a serious flood 3months ago. This flood was not I think user error but occurred in a fast current on the surface while descending a shot line, I believe the long macro port attached got knocked and the current flow forced water past the oring that on the surface was not pressure sealed. The vacuum device should and has on 18 dives so far prevented a flood this has included backward roll RIB entries and occasional giant stride of the back deck.

Re releasing vacuum and opening housing causing a few drops of water to enter, yes I have noted this and it is important to rinse and dry the outside prior to opening but not a major problem.

I would echo the sentiments about Bill being easy to work with and get what you want to install in your camera, thanks Bill

Tim Digger

Backscatter just put up a video of the product 2 days ago. It covers installation and how to use it.

Kirk

Great video. I kept getting distracted By the manta ray video in the background. Other than that a great demonstration of the vacuum system

Alas, one or two underwater photographers in the UK got a bit angry when I mentioned the Hugycheck vacuum system in the past...but then they import alternative brands of housing! Don't know why they get cross. Evidently there is no patent on the system...

It is for sure great that there are no Patents on this system...

In my humble opinion all Housing should come with a system simlilar to this!

It reduces the risk of floods and I am pretty sure that all of us that once had a flood would agree

I just find it a pity that it takes until midlle of May, or so, until the electrocic version is out!

Alas, one or two underwater photographers in the UK got a bit angry when I mentioned the Hugycheck vacuum system in the past...Don't know why they get cross.

Well John your picture is on the front page of the Hugy site. Some could wonder if you have a financial incentive to mention it here.

Cheers,

Steve

" Changing the pressure inside of your housing at sea level using a pump is different than changing the pressure outside of your housing at depth using seawater."

Assuming that the inside of the housing is always at a lower pressure that the out side,

then only difference I can see is the size of the water molecule compared to an air mole.

And that is why commerical leak detectors use helium!

Well John your picture is on the front page of the Hugy site. Some could wonder if you have a financial incentive to mention it here.

 

Cheers,

Steve

I got the same payment that Eric paid me to post on Wetpixel...(European readers should be aware that corruption is evidently quite normal in the ex-colonies. )

I look after my kit. Here's a recent picture of me at work (Courtesey of Bob Semple, Halifax, Nova Scotia.)