Pressure

[Paul r s]

Whilst driving home this evening I had a thought that I wasn't sure of the answer.
Obviously I'm aware of pressure underwater etc.

but (for example)
(1) if I took my camera housing down to 20m and had an old analog depth gauge inside would the needle move

(2) what about in your drysuit ? Because wouldn't the drysuit surround you in an neutral atmospheric pressure

(3) if neoprene gloves worn under dry gloves (bungee installed to allow air to migrate), as you descend would the neoprene begin to compress

(4) if a 40m rated camera housing was installed with its only gas supply that acted the same way as an adv and opv from a breather. Would it then be able to go much deeper ?

[nickb]

1) No
2) Yes - No, it's ambient
3) Yes
4) Yes - but.....

[Garf]

1) No
2) Yes - No, it's ambient
3) Yes
4) Yes - but.....

lol, good answer.

[dwhitlow]

Agreed with 1-3 but

4) not relavent,.

the depth rating of cameras is the depth at which they will work as specified. this will go deep but buttons might stick.
(my 40m rated camera housing worked flawlessly at 70m)

[Paul r s]

Wouldn't the pressure in the gloves be 1bar, meaning the neoprene gloves wouldn't compress ?

[Barrygoss]

Wouldn't the pressure in the gloves be 1bar, meaning the neoprene gloves wouldn't compress ?

Dry gloves, a bag if air round your hands. At ambient pressure
B

[nickb]

I'll expand on the short answers above:

1) Think about Boyle's Law - the volume remains constant (pretty much, it may change minutely), therefore the internal pressure will remain constant. Which is what we desire from a camera housing. A depth gauge measures depth indirectly - what it actual measures is the relative change in pressure. In this case, none - therefore no depth change.

2) When we descend, we need to add gas to our suit in order to maintain the volume of the suit and prevent squeeze, which is uncomfortable and reduces thermal insulation. If you were to ascend from 10m to the surface with the suit valve shut, the volume of gas inside the suit would double. It's the pressure that keeps the gas volume reduced, Boyle's Law again. The pressure inside the suit is the same as the pressure outside the suit, i.e. ambient. Therefore the gauge would show the correct depth.

3) The gloves would compress for the same reason that the depth gauge would register the actual depth, they are responding to the ambient pressure. The gas surrounding them is having the exact same effect as the water would if the dry gloves weren't there.

4) The vulnerability of a camera housing will be in the integrity of the housing body or, more likely, the o-rings and buttons. If the pressure inside can be equalised with the outside water pressure in the same way as the dry suit above, that weakness is eliminated. This is why a CCR can be taken to extreme depths without the hoses collapsing. The problem with operating a camera housing like this would be the camera itself. Clearly, raising the pressure at which the camera is operating will ultimately cause a problem with the camera itself.

[Hot Totty]

Yet again nick beats me to the answer http://www.pic4ever.com/images/www_MyEmoticons_com__fishing.gif

[dwhitlow]

Yet again nick beats me to the answer http://www.pic4ever.com/images/www_MyEmoticons_com__fishing.gif
getting slow are we? http://www.pic4ever.com/images/Banane21.gif

[Hot Totty]

getting slow are we? http://www.pic4ever.com/images/Banane21.gif

http://www.pic4ever.com/images/shame.gif

[dwhitlow]

http://www.pic4ever.com/images/shame.gifhttp://www.pic4ever.com/images/hippo.gif

[Spirit of Guernsey]

I have had my mobile phone inside my drysuit for the last hundred or so dives, doesn't seem to effect it, so safe to assume that a camera would be the same. Unfortunately, they are not too fond of getting wet. If someone was to make a camera housing with an ambient pressure regulator, or even an ambient +0.1bar regulator, it would work without risk of flooding.

[Scuba steve]

Unless you forget to turn on the cylinder ;-)

[Elvis]

I thought a number of people have killed phones (especially "glass" fronted smart phones) by leaving them in under suit pockets, etc.?

[Garf]

I thought a number of people have killed phones (especially "glass" fronted smart phones) by leaving them in under suit pockets, etc.?

oh dear, that's unfortunate news, mine comes with on most dives.

[Elvis]

oh dear, that's unfortunate news, mine comes with on most dives.

Might just be hogwash then.

[Spirit of Guernsey]

The only one that I killed was when I accidentally left it in my thigh pocket.

[Tim Digger]

1) No
2) Yes - No, it's ambient
3) Yes
4) Yes - but.....

I had to think a bit about 3) Cos I wear "normal" undergloves in my dry gloves not neoprene. They dont compress because the air from the suit freely percolates through the material maintaining the loft. Of course the bubbles in neoprene undergloves do not communicate with the air under the outer dry glove and so are compressed. So while these fancy neoprene under gloves may be good for insurance in case of glove holes they will be less good as insulators at depth? Anyone disagree? Have I got it wrong.
Tim Digger

[ziggi]

If one enters a cave system at say 40m and the cave has an incline of say 10m what depth will your gauge read?

[Kermit]

1) No
2) Yes - No, it's ambient
3) Yes
4) Yes - but.....

Not strictly true for 1). You would expect a small rise in pressure as the housing reduces slightly in volume (Hooke's Law) due to external pressure. It all depends on the flexibility of the housing material and the rigidity of it's design.

[nigel hewitt]

I thought a number of people have killed phones (especially "glass" fronted smart phones) by leaving them in under suit pockets, etc.?
I've heard of it and I can quite believe it but when mine inadvertently dived in my undersuit pocket it showed no problems.
However the memories of problems can hang around long after the susceptible models are long since scrapped.

[Spirit of Guernsey]

My phones have done hundreds of dives in undersuit pockets, without any ill effects. Drysuit pockets are not as successful.

[matt]

Whilst driving home this evening I had a thought that I wasn't sure of the answer.
Obviously I'm aware of pressure underwater etc.

but (for example)
(1) if I took my camera housing down to 20m and had an old analog depth gauge inside would the needle move

No, because it is not flexible.


(2) what about in your drysuit ? Because wouldn't the drysuit surround you in an neutral atmospheric pressure

Yes, because you equalize it as you descend.


(3) if neoprene gloves worn under dry gloves (bungee installed to allow air to migrate), as you descend would the neoprene begin to compress

Yes, this is the same as #2.


(4) if a 40m rated camera housing was installed with its only gas supply that acted the same way as an adv and opv from a breather. Would it then be able to go much deeper ?

Yes, because it would be equalized. It may however not work. You could perhaps also break the camera.

[notdeadyet]

Yes, because it would be equalized. It may however not work. You could perhaps also break the camera.

It has been done in the past in industry. The big danger is that the OPV fails and the housing becomes a bomb on the surface.


Sent from my GT-I9300 using Tapatalk

[MikeF]

compensated housings are a bog standard fudge for taking shallow water housings and getting them deeper. done it loads of times but with oil filled enclosures fitted with a small bladder of oil rather than gas. I've used essentially standard stainless steel budenberg gauges at 2000m.

as NDY says the problem with doing this with gas is the fact that the housing may go boom when you recover it. It's an issue with any gas filled enclosure that is subjected to pressure, even without actively pressurising the housing any leak will pressuriss the interior and when the unsupecting operator starts unscrewing the housing they may suddenly get a face full of lid. there have been quite a few cases of transponder housings going bang when trying to fit new batteries and it's the reason syntactic foam buoys are used in the subsea industry rather than trawl buoys as trawl buoys occasionally leak subsea, internally pressurise and go bang after recovery. Be wary when opening sealed umbilical battery housings, especially if it mysteriously died, and point the lid away from yourself while doing it.

A modest amount of fixed overpressure may actually make the possibility of a leak greater during descent as you hit the point where the internal and external pressures equalise. most leaks on housing taken subsea occur in the first few metres from the surface due to the seal not having enough external pressure to energise and a standard fudge is to vacuum the housing to essentially pull the seal into contact with the sealing faces prior to deployment.