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tc_rain

Second thoughts about vacuum systems

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I bought a brand new Canon 70D and Ikelite housing. Worried about potential floods, I had Ikelite drill the housing and add a Leak Sentinel V3 vacuum system. An hour before my first dive with the system, I assembled the rig and activated the V3. It signaled a green light and I packed up my vehicle and drove to a dive site (was in Bonaire). Right before getting into the water, I checked the V3 again and observed a green light. Everything seemed fine as I was happily snapping away; checking the V3 occasionally throughout the dive and seeing it still was displaying a green indicator (vacuum holding). Approximately 30 minutes into the dive, I noticed a small droplet of water inside the housing. I look at the V3 again and it is still green. I immediately abort the dive and head for the surface. After a long surface swim with the camera out of the water, I make it to shore. By this time the housing is completely fogged inside and I fear the worst. I dry off the outside of the housing and try to open it but it wont open. The V3 is still displaying a green light. I bleed off the vacuum through the V3 and hear the hiss of air rush into the housing. I then manage to open the housing and find 3 or 4 tablespoons of seawater inside. Fortunately, the camera and lens were unharmed. I return to my room and fired off an email to Ikelite. I must say they are fantastic when it comes to customer service. They sent an immediately reply and even offered to send me a loaner housing to Bonaire. Due to all of the trouble of bringing two housing home through carry on I declined but it was very nice of them to make such an offer.

While in Bonaire, I spoke with the owner of the camera shop at Buddy Dive and explained what happened. He stated he has been taking underwater photos for 20+ years with Ikelite housings and has never had a problem. He does not like the vacuum systems and explained how it draws / pulls on an O-ring differently than they were designed. He also said he understood the concept of the vacuum but it bothered him because it wants to pull air / water into the housing. He felt the vacuum systems were unnecessary.

 

After talking with the camera shop owner and the fact my housing leaked underwater while still holding a vacuum, I am beginning to wonder if the vacuum system is worth having. Am I looking at this wrong or missing something? By the way, the housing was sent back to Ikelite and I was informed the shutter gland had worked loose. They rebuilt the gland and replaced all electronics free of charge. I cant say enough good things about the way they handled everything.

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If in fact the leak was caused by the shutter gland, are you saying that you suspect the vacuum system contributed to its failure? It's not obvious to me how the two could be correlated.

 

BTW I've been using the same Leak Sentinel for over a year on a Nauticam housing without issue.

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That is not what I am saying. I am saying it did not detect or alert me of the leak like I thought it would. I thought it would turn red underwater or at least above water if there was a leak.. Maybe I put too much faith in the concept. To add to that, i didn't think of this until typing this response, maybe the vacuum ascerbated the leak. I honestly don't know. That is the purpose of this post. I guess I really don't know what I should have expected. I thought if I got a green light above water I woud be safe diving with it. I also thought it would indicate if there was a leak underwater. I am not trying to say anything bad against a vacuum system, I just want to understand the reasoning of what happened.

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You've got me stumped but I'm no expert.

 

Reach out to Miso (very responsive) at Vivid and get his thoughts.

 

I'm interested in what you find out.

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i would think the o-rings are designed for negative pressure inside the housing. when diving the pressure inside the housing should decrease thus acting like a vaccum. i opted for the vacuum system on my new housing to reasure i dont have any major leaks from the port and other potential leak sights to prevent a major flood. im thinking a positive pressure system would be really complicated and the pressure would equalize at some depth point.

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Any chance this is related to warm humid air condensing in a water cooled housing?

 

Sounds like a bit too much water for that scenario:(

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The forces on the housing are a function of the pressure difference between the inside and outside of the housing. A vacuum of 10 psi at the surface is the same as going down 20' or so with a housing that has no vacuum inside. So pulling a vacuum before diving is the same as diving a bit deeper.

 

Having said that, I can see that if you spring a leak at depth this could be a problem. Lets say you evacuate the housing to 10 psi of vacuum (i.e. 4 psi absolute), and lets also guess that the alarm goes off if the vacuum drops to 9 psi (i.e. 5 psi absolute). In order to do this you need to compress the air in the housing to 80% of it's original volume. How do you do that? By filling the rest of the volume with water. I am guessing that the alarm deadband on these things is less than 1 psi, but you get the idea. I don't know what the actual alarm setting of these systems is, but a small pressure change can amount to a fair amount of water in the housing when there is a leak underwater.

 

I think the real value of these systems is that you can find a leak before you go into the water. If the leak starts once you're in the water I don't think they're likely to help much.

 

I still think they're great and my wife and I have them on both of our housings.

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I think you are onto it. If the gland failure happened once already under water, then no additional air could get into the housing, thus not raise the pressure (decrease the vacuum) enough to trigger the alarm.

 

But another interesting issue raised above by junior5 - once sealed, how is it possible for the pressure inside a rigid housing to significantly change at depth? That would seem to violate the laws of physics. Not counting temperature effects of course.

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I think you are onto it. If the gland failure happened once already under water, then no additional air could get into the housing, thus not raise the pressure (decrease the vacuum) enough to trigger the alarm.

 

But another interesting issue raised above by junior5 - once sealed, how is it possible for the pressure inside a rigid housing to significantly change at depth? That would seem to violate the laws of physics. Not counting temperature effects of course.

 

The only way the pressure can change is either a huge temperature change, not realistic, or something leaks into the housing to displace volume, and enough has to leak in to compress the air in the housing enough to make a big enough pressure change to trip the alarm. In other words a fair bit of water.

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more water would have to enter the housing the deeper you go in order to change the light. i mainly rely on my green light indicator before getting into the water. i think it is helpful before each dive. a port or something could have broken a seal between dive spots. the green light being on reassures a seal hasnt been broken

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I'm with both of you - if the light stays green for a half hour or so before the dive, then the housing is sealed and the o-rings are safe unless something fails, which is of course impossible to predict or protect against. All in all, the vacuum system gives me much greater peace of mind

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This one seems pretty obvious (to me...): Vacuum systems give you a pre-dive security check against user errors, i.e. twisted o-rings, a hair on an o-ring etc. In your case the shutter gland was loose. Would you have noticed without a vacuum system? No. Could you have noticed with the vacuum system? Yes - IF you had operated/knocked/twisted the shutter button while on land. Does anyone do that (operate all housing controls pre dive excessively)? No.

 

And IMHO the camera shop owner is completely wrong! It does not make any difference if you pull from inside the housing (= apply a vacuum) or push from outside (= apply water pressure). So the idea that the o-rings are "sucked in" is nonsense. And nonsense especially if you think about the relatively small degree of vacuum you apply with your pump.

 

Bottom line: If you want to avoid a flooding don't take your housing under water :-)

 

Just my two Euro-Cents

Jock

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agree with Jock. I have the backscatter vacuum, and find it very useful as a pre-dive check. I pull the vacuum, and check the pressure (ideally the following morning) to see if the vaccuum has dropped to identify any major leaks.

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I'm with Jack and Nortoda1. Having had the Vivid for about a year and done roughly 100 dives with it, I would not now want to live (or dive!) without it.

 

I have had one or two weird readings where it has been green maybe overnight or at least the last 20-35 mins and then started to flash green/red when underwater. Talk about a panic-inducing moment. But there has been no leaks.

 

I haven't been able to pin down the reason but suspected some sort of temperature change. This happened in Bonaire a couple of weeks ago.

 

I must admit I'm slightly dubious too of the advice you got at Buddys......

Edited by TimG

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Much said already about the vacuum problem. But I think its theoretically possible that a drop of water enters into the housing along a shaft or gland with no apparent change of the vacuum inside. Another point is that in the pre-dive check the vacuum should also be tested by turning levers, moving shafts in and out, pressing buttons etc.

Edited by albert kok

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Wetpixel shooters,

 

I won't pretend to know all about the various vacuum systems on the many choices of housings out there. I shoot Ikelite (for decades and now a Canon SL1 housing) and have never installed one. As recommended for all housings I check the tightness of control fittings, push buttons etc. usually on dive 1 after flying to a destination.

 

Any opaque housing likely benefits from a vacuum system depending on how familiar the user is with pre-dive set and checks. But they aren't perfect as even some other posts on leaks and floods have previously detailed.

 

The only other thing I'll say is John at Buddy Dive has more experience seeing all manner of housings and extras than the total community here. So I think someone who's seen what works and doesn't work probably has a better real world view is all.

 

If you love your vacuum system and it works for you that's fine. But likely thousands of dives are (were) made for decades without them. So it's usually in how someone was shown to set their system up and then followed that procedure being most important.

 

YMMV..........

post-244-0-47279100-1427460012_thumb.jpg

Edited by dhaas

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I have emailed Miso for the nominal set points on the sensor in the LS3. I have had one for about 18 months and LOVE it. As I recall, Miso told me at one time that it takes a 10% reduction in internal pressure to turn on the green light. I'll confirm that, but:

 

Assume the housing is at 15 psia (that's absolute). Then the green light comes on at 13.5 psia with the removal of 10% of the volume inside the housing. 10% of the volume of the housing is a lot of water, at least for my Aquatica with the dome port installed. So to get the red light to come on, you need a portion of the 10% in water volume to be introduced into the housing. So, IMO the LS3 (or any other vacuum system) isn't going to help much in dealing with a leak that starts after you're underwater. It's main value is to insure that the system is secure before getting in and, to a much less extent, during the first few feet of descent before the outside pressure firmly seats everything.

 

BTW I still have my electronic leak detector installed in my housing. That will tell me as soon as any water is introduced into the housing-long before the pressure increases to trip the red light. That may save the internals. As both perform different functions, having both methods gives me max chance of avoiding a flood.

 

I'll post an update once I hear from Miso,.

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Just got a response from Miso. Here are the facts on the LS3:

 

First, the sensor measures the internal pressure as soon as it's turned on. This is the reference pressure. Assume that the reference pressure is atmospheric, i.e. 1000 mbar. To get the blinking green light, one must reduce the internal pressure by 200 mbar, i.e. go from 1000 mbar to 800 mbar by pumping down. Once at blinking green, an increase in pressure of only 5 mbar will trigger the alternating colors blinking. This is a very small change and will be achieved by the introduction of about 6 ml of water per liter of internal housing volume. My SWAG (sophisticated wild-ass guess) is that the typical housing volume with dome port is 1.5 to 2.0 liters, less with flat port. I don't plan to fill my housing with water to test this estimate.

 

Also from Miso: He has a new product, the LS4 with temp. comp and other features that are very nice. He is offering the LS4 circuit board to current owners of LS3 for 50 euros. The LS4 board is a direct replacement for the LS3 board. The other nice feature is that it allows you to turn the sensor light off and retain the reference set point for the future. With the LS3, when you turn it off, you lose the reference set point and must equalize the housing before turning the LS3 back on. Then you have to pump it down again. The LS4 will extend time between battery changes. PM me if you want more info.

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To apply what divengolf mentioned on the LS4 (plan to do a review after more use): the fact that it stores the current pressure means you can create a vacuum the night before a dive, turn it off overnight (conserve battery), then turn it on the next day before your dives to make sure it's held the vacuum over night. Miso added some very nice features to the LS4.

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I dive and photograph from 2011 on with vacuum checked housing and made about 300 dives with Hugyfot and newly with Nauticam check housings and i never had that issue,

and i never flood any housing from 2006 on in about 1000 dives with various hosuing (Hugyfot, Nauticam, Canon, Ikelite, Patima)

 

I believe that if there is a very, very small leak on a not tight/leaking gland/button/lever there may be the way that the vacuum inside sucks over some time a small drop in,

BUT most likely this his would be the same without vacuum system as the outside pressure would push the water in.

 

I had only twice a pressure drop and alarm, both caused because the housing was not vacumized enough and the change in ambient temperature triggered the alarm.

 

As there is a 10% pressure drop before the alarm triggers it would be possible that water instead of air get sucked in and the only solution for that is:
a) load and vacumize the housuing the evening after or as long as possible
b) to be anal; check and move all the glands, buttons, levers and connectors

c) NEVER jump in the water with the camera, have it handed to you when you are in the water

d) NEVER leave the camera in the rinse tank, rinse it after the dive and store it in a cooler/box with water or wrapped in a fluffy towel in the shade

 

 

The only 2 things i flooded are
one D-2000 strobe because i pinched the o-ring while screwing on the battery compartment
one Z-240 strobe for unknown reasons, there was a hair crack in the battery compartment cap where some drops leaked in and shortened the electronics

Both strobes would have saved IF they had a vacuum leak detector...

 

Chris

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It's not 10% difference that triggers the alarm, but the 5 mbar pressure rise from the green blinking point, which is 200 mbar below the ambient pressure measured at startup.

 

Whether the housing is vacuumed or not doesn't really matter, except it changes the housing's depth rating for 2m (if vacuumed to -200 mbar), and that is also more or less unimportant, as nobody makes the housing which will crash at exactly that depth. The only thing that matters is a pressure difefrence, so a vacuumed housing will function exactly the same as a non-vacuumed 2 meters deeper. So, the Buddy dive's argumentation makes no sense, as the o-rings will behave exactly the same, it's just a question of depth. All housings are designed to function with higher pressure on the outside, and the vacuum only helps keep doors and domes tight in place.

 

How much water must enter the housing before the alarm is triggered depends on how many pump strokes are pulled after the LED starts blinking green. As V3 doesn't have the temperature compensation implemented, it is a kind of tradeoff between the amount of water and a possibility of false alarm due to temperature change, but generally, one stroke should suffice to avoid false alarm in average sized housing, and to keep the water amount at bay. 6ml of water per liter of the housing volume is not an enormous quantity of water, and I think it's hardly enough to trigger any leak detector. Any sanitary pad will handle much more, and I'd suggest using one no matter if you have LS or not.

 

V4 solves all the problems above, as it measures the pressure when the pumping stops, and takes that as a reference, so it doesn't really matter how many strokes you pull after the green LED starts blinking (but don't go overboard for obvious reasons).

 

Of course you should operate the buttons and controls during the test, I never put that in the manual as that seemed a no brainer to me, LS is just an electronic replacement for a good ol' bucket;) And that was obviously the cause for the problem tc_rain had, the housing was sealed until the lever was operated...

 

Cheers,

Miso

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And IMHO the camera shop owner is completely wrong! It does not make any difference if you pull from inside the housing (= apply a vacuum) or push from outside (= apply water pressure). So the idea that the o-rings are "sucked in" is nonsense. And nonsense especially if you think about the relatively small degree of vacuum you apply with your pump.

I wouldn't be so sure. This idea intrigues me and I don't have an answer, but sucking an 'O' ring into place might well result in the 'O' ring seating differently than pressure pushing it into place will - the forces at work may well be being applied in different ways. Clearly this doesn't cause problems most of the time, but that said, in my experience the vast, vast majority of floods are usually down to very obvious reasons (and more often than not simple user error I'm afraid!). And many floods are caused by rushing which would probably mean ignoring the vacuuming step anyway. Whilst I suppose I could fit a vacuum system and have thought about doing so, I've always shied away from doing so as I've always thought that good pre-dive preparation doesn't need yet another step - its time consuming enough as it is. Depending where it enters 6-12ml of seawater could do a lot of damage so it makes sense to see a vacuum system as a pre-dive check only as far as I can see from what has been said. Interesting thread.

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is the force that'll move the o rings not just the pressure difference?

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is the force that'll move the o rings not just the pressure difference?

Exerting a force by sucking the 'O' ring inwards from decreased internal pressure when the exterior is subject to air pressure may not be the same as increasing liquid pressure applied from the exterior - I say might, I'm not sure what if any the difference is. Also you would need to take into account the physical 'pre-load' on the 'O' ring due to the housing fastening system. As I said it intrigues me. Sounds simple, but is it?

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Although vacuum systems can detect a significant leak during a dive, I feel that a moisture sensor is a far more sensitive indicator of a leak which has occurred DURING a dive. The vacuum systems show their greatest utility (IMHO) in 1. Identifying that your system is properly sealed pre-dive, 2.Preloading the O-rings, thereby minimizing blow-by of water at the surface on entry or surface swims. I use both systems on my housings.

Doug

Edited by diverdoug1
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