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Dumb Question: Pressurizing a housing?


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#1 Dan Schwartz

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Posted 17 October 2007 - 08:07 AM

OK folks, here's my Dumb Question Of The Week:

Has anyone tried to pressurize an underwater housing, to reduce the stress on the seals? If so, did the air come off the SCUBA tank via the octopus; or was it supplied by a small, dedicated bottle, with, say, moisture-free nitrogen? Of course, one would need an automatic bleed-off valve for the ascent, yada yada yada...

It would seem that having a small pressure regulator to keep the air inside the housing just a few inches WC above the pressure of the surrounding water would make life easier.

The analogy would be a conventional camera housing is to helmet diving as a pressurized camera housing is to SCUBA diving.

Thanks!
Dan

[PS: Many years ago at Scott Paper, when we had to install a motor control center or instrument cabinet in a wet (& lightly corrosive at times) location, we would pump dried instrument air into the cabinet to about an inch or so of pressure to keep the outside atmosphere, well, outside.]

Edited by Dan Schwartz, 17 October 2007 - 08:12 AM.

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#2 Paul Kay

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Posted 17 October 2007 - 09:20 AM

Dan

This has been discussed on wetpixel before but the simple answer is:

J Y Cousteau used a pressurised system for his cine cameras many years ago (late 40s, early 50s)!

Most modern housings use 'O' rings together with a preloading latch or lock system which increases in efficiacy as more external pressure is applied. Its simple, tried and tested, works very effectively and unless there are very good technical reasons to utilise a pressurised system, there seems little point in reinventing the wheel and complicating things at the same time.
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#3 Dan Schwartz

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Posted 17 October 2007 - 09:49 AM

Well, I said this was a dumb question! -_-

More...

Dan

This has been discussed on wetpixel before but the simple answer is:

J Y Cousteau used a pressurised system for his cine cameras many years ago (late 40s, early 50s)!

Most modern housings use 'O' rings together with a preloading latch or lock system which increases in efficiacy as more external pressure is applied. Its simple, tried and tested, works very effectively and unless there are very good technical reasons to utilise a pressurised system, there seems little point in reinventing the wheel and complicating things at the same time.


Actually, I can give you one technical reason to do this: With the multitude of menu buttons on modern digital cameras, having a pressurized case would allow for a flexible (silicone or LDPE) membrane back, making it asy to push all of those buttons... As opposed to having a housing penetration for each one.
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#4 echeng

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Posted 17 October 2007 - 09:57 AM

Well, this is sort of the opposite, but Howard Hall, Bob Cranston, Norbert Wu, and Jim Abernethy (after seeing the others' rigs) all create (measured) negative pressure in their housings to ensure that there are no leaks before taking them underwater.
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#5 MikeO

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Posted 17 October 2007 - 09:57 AM

Well, I said this was a dumb question! -_-

More...
Actually, I can give you one technical reason to do this: With the multitude of menu buttons on modern digital cameras, having a pressurized case would allow for a flexible (silicone or LDPE) membrane back, making it asy to push all of those buttons... As opposed to having a housing penetration for each one.


Hmmm, well then what do you do with it when it is above water, does the membrane back stick out like a balloon :wub: ? Actually, rather than pressurize housings, there used to be (maybe still is) a device someone sold that actually drew a vacuum on the housing (it was also available for Nikonos). If you could get a good enough vacuum, you knew the O-rings were all seated.

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#6 james

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Posted 17 October 2007 - 09:59 AM

Yes, you could fit your housing w/ a pressure compensated nitrogen bottle and a discharge dump check valve for when you come out (so that you don't blow your o-rings out.

But that isn't required if you diving between 0 and 80 meters as most housings have full function to those depths. If you're going to be diving deeper than 80 meters, then maybe it's a consideration.

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#7 Dan Schwartz

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Posted 17 October 2007 - 10:00 AM

Hmmm, well then what do you do with it when it is above water, does the membrane back stick out like a balloon :wub: ?


Err... Bleeder valve, so it doesn't get "bent" -_-
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#8 MikeO

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Posted 17 October 2007 - 10:01 AM

Well, this is sort of the opposite, but Howard Hall, Bob Cranston, Norbert Wu, and Jim Abernethy (after seeing the others' rigs) all create (measured) negative pressure in their housings to ensure that there are no leaks before taking them underwater.


Wow, the electrons must have seen each other going by on this one -- our posts missed each other by a split second!

Here's the thing I was trying to remember:

http://home.pacbell.net/pac-cam/

Mike

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#9 rtrski

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Posted 17 October 2007 - 10:47 AM

I'm sure I wasn't the first to ask this either...just the more recent first -_-. I wasn't thinking in terms of a membrane back but definitely thought a smaller pressure differential would kind of get rid of issues with spring pressure and depth limits on a housing.

But here's the link to the thread I started on the same topic earlier this year. In the end I thought it was a pretty good discussion and I understood a lot more about housing design (from a 'Popular Science' standpoint - not that I think I could do it!)

http://wetpixel.com/...m...st&p=135624

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Topside, unhoused: Sony SLT-alpha99, Sigma 150-500mm + 1.4TC (Saving for Sony 70-400 G2), Sigma 15mm diagonal fish, Sony 24-70mm f2.8 CZ, Tamron 180mm f2.8 Macro...all the gear and nary a clue...


#10 loligo

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Posted 17 October 2007 - 11:21 AM

There was a product in the nineties, manufactured by a camera dealer in Southern California, which served to pressurize housings or even a Nikonos camera by means of a box-like instrument installed on the housing exterior using an unused bulkhead opening. The company furnished either a hand pump or electrical version which would pre-compress the o-rings -- through a valve -- to simulate something like ten meters of depth. There was also a fail-safe in the form of a visual alarm which would illuminate if the initial pressurization failed. It was quite popular in its time . . .

#11 Dan Schwartz

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Posted 17 October 2007 - 11:24 AM

OK, I went through the Weird idea...POSITIVE pressure housing, ...anyone ever considered it?? thread; and I have a couple observations:

1) It boggles my entire mind how many SCUBA divers didn't grasp the concept of dynamic air pressure adjustment. Go back to my original post, and you'll see:

The analogy would be a conventional camera housing is to helmet diving as a pressurized camera housing is to SCUBA diving.


If you treated your lungs the same way you treat your camera housings, you'd be gone in 60 seconds! -_-

OK, maybe the above sentence is a bit brash.

Let me try again: It would be quite easy to use a pair of regulators to
  • Push air into the housing during the descent, keeping it a fraction of a PSIG higher than the surrounding water pressure
  • On the ascent, a bleeder valve burps out the air, to maintain the slight pressure differential.
2) My second observation is that nobody making housings seems to know what a "Zeus" (or "Buckeye") fastener is. If you've ever watched an IndyCar or other open wheel race, you'll see that when they have to remove the engine cover, they simply twist the screw a 1/4 turn. Give me a few minutes and I'll go out to the garage and take a couple snapshots of them; and post them below...

[It helps that my fiancee's father is storing his restored 1962 Leffler sprint car in our garage! ;) ]

Cheers!
Dan

I'm sure I wasn't the first to ask this either...just the more recent first :wub:. I wasn't thinking in terms of a membrane back but definitely thought a smaller pressure differential would kind of get rid of issues with spring pressure and depth limits on a housing.

But here's the link to the thread I started on the same topic earlier this year. In the end I thought it was a pretty good discussion and I understood a lot more about housing design (from a 'Popular Science' standpoint - not that I think I could do it!)

http://wetpixel.com/...m...st&p=135624


Edited by Dan Schwartz, 17 October 2007 - 11:25 AM.

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#12 loligo

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Posted 17 October 2007 - 11:33 AM

It is not any misunderstanding on my part. The device I mantioned in the last post serve to "vacuum-seal" the housing , not introduce air into it. The hand-pupm served to <i>remove</i>air. I saw it demonstrated a number of times . . .

OK, I went through the Weird idea...POSITIVE pressure housing, ...anyone ever considered it?? thread; and I have a couple observations:

1) It boggles my entire mind how many SCUBA divers didn't grasp the concept of dynamic air pressure adjustment. Go back to my original post, and you'll see:
If you treated your lungs the same way you treat your camera housings, you'd be gone in 60 seconds! -_-

OK, maybe the above sentence is a bit brash.

Let me try again: It would be quite easy to use a pair of regulators to

  • Push air into the housing during the descent, keeping it a fraction of a PSIG higher than the surrounding water pressure
  • On the ascent, a bleeder valve burps out the air, to maintain the slight pressure differential.
2) My second observation is that nobody making housings seems to know what a "Zeus" (or "Buckeye") fastener is. If you've ever watched an IndyCar or other open wheel race, you'll see that when they have to remove the engine cover, they simply twist the screw a 1/4 turn. Give me a few minutes and I'll go out to the garage and take a couple snapshots of them; and post them below...

[It helps that my fiancee's father is storing his restored 1962 Leffler sprint car in our garage! ;) ]

Cheers!
Dan



#13 Dan Schwartz

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Posted 17 October 2007 - 11:48 AM

2) My second observation is that nobody making housings seems to know what a "Zeus" (or "Buckeye") fastener is. If you've ever watched an IndyCar or other open wheel race, you'll see that when they have to remove the engine cover, they simply twist the screw a 1/4 turn. Give me a few minutes and I'll go out to the garage and take a couple snapshots of them; and post them below...


OK, here is a picture of a pair of Zeus cam-lock fasteners. The one on the left has a conventional slot head, while the one on the right has the (less aerodynamic!) wings. The valve out of the Leffler's 306 Chevy V8 is there simply because it looks cool! -_-

    Posted Image

Cheers!
Dan
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#14 rodriguezfelix

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Posted 17 October 2007 - 11:59 AM

Well, this is sort of the opposite, but Howard Hall, Bob Cranston, Norbert Wu, and Jim Abernethy (after seeing the others' rigs) all create (measured) negative pressure in their housings to ensure that there are no leaks before taking them underwater.


Actually once I think about doing this, and this is what I concluded:

Since Caracas (Venezuela) is above 700mts of altitude, if I arm my rig here and then drive to the beach, this will create a little negative pressure inside the housing, the way that If when I came to the beach I can not take my port out, there are no leaks and when I return home I can easily open my housing again... of course this leave me with the inability to change anything in my rig including batteries, lens, or anything else, so this can be done for a couple of dives day, and i don´t know how much negative pressure i am creating... so it could be a risk.

Now I wonder... how this guys create the negative pressure inside their housings?

#15 Dan Schwartz

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Posted 17 October 2007 - 12:15 PM

Wow, the electrons must have seen each other going by on this one -- our posts missed each other by a split second!

Here's the thing I was trying to remember:

http://home.pacbell.net/pac-cam/

Mike


You mean this?

Posted Image

Sorta looks like this item on eBay: Posted Image

Edited by Dan Schwartz, 17 October 2007 - 12:19 PM.

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#16 Dan Schwartz

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Posted 17 October 2007 - 12:26 PM

Helge,

Your warning (in the other thread; quote copied below) is duly noted.

Thanks for the heads-up!
Dan

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 [emphasis added: DLS] 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.

Helge ;-)=)


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#17 craig

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Posted 17 October 2007 - 12:50 PM

Those are DZUS fasteners, not "Zeus".

The studded leather ring would make some nice mojo for the rig.
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#18 davichin

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Posted 17 October 2007 - 01:03 PM

Hugyfot has this:

http://www.unterwass...66bf7a59108fa66

which does the opposite
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#19 Dan Schwartz

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Posted 17 October 2007 - 01:28 PM

Those are DZUS fasteners, not "Zeus".


Jack (my fiancee's father) always calls them "zeus fasteners..." But what would he know.

Cheers!
Dan

PS: He was a mechanic in 1963 for A.J. Agajanian when his car, the #98 driven by Parnelli Jones, won the Indy 500...

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#20 craig

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Posted 17 October 2007 - 01:53 PM

Jack (my fiancee's father) always calls them "zeus fasteners..." But what would he know.

Hopefully Jack wasn't spelling it like you do, but I don't know what he knows.

I worked with "zeus" fasteners, too, when I was an auto mechanic and helped with my boss's race car. I knew how to spell it AND pronounce it. When I was told to get "zeus" fasteners, I looked for the box with "Dzus" written on it. -_-

Look it up if you don't believe me. Here's a start.
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