New Housing "Airlock" Vacuum from Backscatter

[E_viking 30]

I was wondering if there would also be the additional advantage of less condensation risk. Lower pressure means lower partial pressure of water vapour, unless the pressure drop is too small to be significant.

 

Bart

 

Hi Bart,

 

There should be less condensation risk while diving, since more humid air is sucked out, causiing less overall humidity in the Housing.

This is however only an issue for plastic Housings.

 

The 2nd part of condensation is when opening the Housing at the surface. The Air is generally warmer at the surface compared to the water..

With a vacuum system, more air will rush in when opening the Housing after a dive. That gives us a faster temp change, this causes a condensation as well.

If it is only a theoretical problem or a a "real" issue???

An easy way to get around this should be to leave the Camera in the Housing a bit longer than normal.

 

Erik

[Aussiebyron 57]

I believe a vaccum system should be standard on all housings.

 

Regards Mark

[ChrigelKarrer 52]

Yes, i believe also that it should be standard on all housings and this is

one of the main reasons that i will stick with Hugyfot.

There is one more important advantage of this system:
creating a vacuum inside the housing will suck the o-rings in their position and shape.

I believe that slightly out of shape or position o-rings are the main reason for unexplainable flooding on surface

or low depth as the external pressure don't press them on their seat/shape.

 

Chris

[okuma 64]

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?

[FanchGadjo 16]

I guess the quick connector everyone uses is from swagelok (QM2) :

http://www.swagelok.com/downloads/WebCatalogs/EN/MS-01-138.pdf (page 12)

 

(without the nuts)

 

My mission here is done, I shall now fly away.

[Ronyx 6]

DIY anyone?

[ChrigelKarrer 52]

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?

The Hugyfot housing has a screw on cap on the top and to release the vacuum you have dry the external valve assembly unscrew slowly the lower part of the valve assembly to release the vacuum. I never had issues with water get sucked inside the housing releasing the vacuum this way.

 

 

I guess the quick connector everyone uses is from swagelok (QM2) :

http://www.swagelok.com/downloads/WebCatalogs/EN/MS-01-138.pdf (page 12)

 

No, not everyone; Hugyfot is using their own valve assembly who got screwed inside one of the bulkheads.

 

There is a animation on the Hugyfot webpage demonstrating how a/their vacuum system work.

 

Chris

 

 

[FanchGadjo 16]

Chris, you are right. So I should say most systems showed in this topic use

the swagelok quick connector.

 

Here is the Hugyfot valve :

 

[JKrumsick 3]

I wonder about how accurate these systems are - I certainly see the intuitive connection between confirming that the pressure inside your housing using one of these systems not changing confirms that your housing will not flood. But have there been extensive tests confirming the link between these two?

 

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.

[blibecap 29]

Whats the differance?

[Ronyx 6]

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?

[eyu 27]

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????

Edited March 7, 2013 by eyu

[E_viking 30]

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

[denniscloutier 2]

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.

[John Bantin 101]

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.

[E_viking 30]

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

[ChrigelKarrer 52]

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

[Ronyx 6]

Why should there be a difference with pressure for Seawater?

 

/Erik

I don't know but the question was asked.

[Ronyx 6]

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.

[andy_deitsch 17]

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.

[FanchGadjo 16]

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 !

 

[blibecap 29]

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.

[Tim Digger 1]

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

[KirkD 7]

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

 

 

Kirk

[Ronyx 6]

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