Nauticam Vacuum valve - how much vacuum?

[Bevanj 9]

Hey guys and gals,

For those of you with Nauticam vacuum valves and DSLR housings, how much vacuum have you been putting in your housings? Obviously the more vacuum present in the housing after the light turns green, the more water which will enter the housing before it starts flashing yellow in a worst case scenario. Yet, with not enough vacuum, it seems to make it more prone to falsely giving a yellow flashing light indicating a leak even though it is supposedly temperature compensated. Go figure...

I've been using the standard Nauticam pump to get my housing past the yellow flashing light, into the green. Then, I bleed air into the housing using the valve at a very very slow rate until it just starts flashing again. Then, I chuck the pump back on, and give it one pump to get it back into the green again. Seems to do the trick for me.

Bleeding air in after this setup seems to indicate very little leaking required before it starts flashing yellow, but I have yet to have it false trigger after this.

How are other people doing things?

Bevan

Edited February 13, 2018 by Bevanj

[Ryan 48]

The circuit is definitely temperature compensated, and if you are seeing a solid green go back to flashing yellow the most likely cause is that you actually have a very slow leak, not an issue with the temp comp in the circuit.

 

Our recommendation is to stop pumping when it turns green. Pump too much, you defeat the purpose of the monitoring.

[Bevanj 9]

Thanks Ryan,

The one time I've seen it happen, I definitely didn't have a leak. Housing had sat for hours with a green light before getting in the water, and changed to yellow as soon as it chilled off on entry. Put it port down above my head on descent with no sign of water. The inside was bone dry after opening after over an hour in the water.

Bevan

Edited February 13, 2018 by Bevanj

[TimG 62]

Is it actually possible to have a partial vacuum? You either have a vacuum or you don’t, right? Do these valves create a vacuum or do they actually produce a lower pressure inside the housing which the device monitors and reacts to if that pressure increases through a leak?

 

Or am I being an utter pedant and it doesn’t mattter anyway!?

[bvanant 189]

When it comes to a vacuum there is no boundary, pressure inside the housing is a continuous variable. The electronics inside the housing monitor the pressure and turn green if the pressure is less than x. When the pressure rises above x it first turns yellow then red as the pressure gets higher. I don't know the exact pressure where the green light turns on (it depends on the temperature and also on the variability of the actual electronics) because I am too lazy to actually measure it, but my three copies of the Nauticam electronics do have different pressure settings, at least by a bit.

 

Cheers

 

Bill

[tursiops 81]

Is it actually possible to have a partial vacuum? You either have a vacuum or you don’t, right? Do these valves create a vacuum or do they actually produce a lower pressure inside the housing which the device monitors and reacts to if that pressure increases through a leak?

 

Or am I being an utter pedant and it doesn’t mattter anyway!?

Yes, you are being an utter pedant.

Pulling a vacuum doesn't mean you go all the way to no air molecules inside....it just means there is less pressure inside than there is outside.Yes, it is a partial vacuum. Just like a glass can be partially empty.

[TimG 62]

Oh right - thanks for that.

 

As you can probably tell, I didn't pass the physics exam at school. I can remember - even calculate - partial pressures though

[Deep6 7]

Well! Not to be too pedantic, what we are discussing is reduced pressure. There is a scientific definition for a vacuum which can not be achieved with this apparatus. "Nature abhors a vacuum", but these systems are a really helpful.

[okuma 64]

Bevanj:

 

I believe you are overly concerned about this. We have Vivid units on our housings and use a small hand pump.

I pump till I get a green light and then two extra strokes. We do this 1/2 hour before diving and as long as it stays green, then good to go.

 

Over pumping will eventually cause your housing to collapse and eventually get sucked up into the pump!

[TimG 62]

Well! Not to be too pedantic, what we are discussing is reduced pressure. There is a scientific definition for a vacuum which can not be achieved with this apparatus. "Nature abhors a vacuum", but these systems are a really helpful.

 

 

Ahhh right! Now that makes good sense.

[Alex_Mustard 0]

On my pump (with a pretty dodgy gauge) the pressure required to get a green light on a brand new Nauticam housing was -0.3 Bar.

 

On that housing for the OM-D EM-10 Mk3 that is about 3-4 pumps. On my Nikon D5 housing when using a 230 dome that is about 20 pumps to get the green light!

 

Alex

[tursiops 81]

 

On that housing for the OM-D EM-10 Mk3 that is about 3-4 pumps.

Depends on the lens/port....the 12-50 macro port might add considerable volume to pump down versus a short port for the 14-42, for example. My M10 Mk 1 takes 5-7 pumps, depending on my lens/port combo.

[Bevanj 9]

Cheers guys. Interesting that the green point Alex found is -0.3bar.

 

My question is more how much further to go. Too far, and your housing will be half full of water before the vacuum alarm will trigger. Not enough, and from my experience you get false triggers.

 

Bevan

[pbalves 52]

The best is to have a moisture alarm too.

 

But back to the vacuum alarm, I think that 1 or 2 extra pumps after the green is enough (specially if you sensor has temperature compensation). If you pump more, you take the risk of a small leak not to be detected before the dive.

[DocTock 6]

The following is personal experience only.

 

I was an early adopter of a vacuum system on a Nauticam housing. I had a leak/ vac sensor in my original NA-D90 housing (and now a NA-D800 with leak/vac sensor) so I added a Housing Sentry vacuum plug which came with a MiniVac manual pump with a gauge.

While this is (I believe) a brake fluid tool originally, and I do not know how accurate the exact readings are, the following "data" points have been noticed from the Nauticam leak/ vac sensor indicator light:

 

1. Red state until at least 3mmHg vacuum pressure

2. Yellow indicator between ~3mmHg - ~5mmHg

3. Solid green light at a point beyond ~5mmHg

 

My practice has been to do battery/ memory card/ o-ring maintenance at the end of every day of diving.

I then seal, initiate vacuum, set-up and check function under ~8mmHg vacuum pressure.

It takes me approximately 3-5 squeezes of the MiniVac handle to get from ~5mmHg to ~8mmHg. (More squeezes needed with a 230mm dome, fewer with a 105 port.)

Once complete, I let my whole system sit (under vacuum) until the next day of diving.

If there is still a green light showing in the morning, I feel comfortable that my risk of a leak is low and I proceed with the dive.

 

I used to check the "reading" in the morning, but found, even in tropical climates with high variations in overnight temps (sometimes kept in over AC camera rooms, some open air) there was usually zero to <~1mm variation in 8hrs.

What I did find is I was more likely to lose vacuum by checking the reading, and the reason I no longer "verify" the green light with a reading.

Edited February 18, 2018 by DocTock

[hellhole 18]

The following is personal experience only.

 

I was an early adopter of a vacuum system on a Nauticam housing. I had a leak/ vac sensor in my original NA-D90 housing (and now a NA-D800 with leak/vac sensor) so I added a Housing Sentry vacuum plug which came with a MiniVac manual pump with a gauge.

While this is (I believe) a brake fluid tool originally, and I do not know how accurate the exact readings are, the following "data" points have been noticed from the Nauticam leak/ vac sensor indicator light:

 

1. Red state until at least 3mmHg vacuum pressure

2. Yellow indicator between ~3mmHg - ~5mmHg

3. Solid green light at a point beyond ~5mmHg

 

My practice has been to do battery/ memory card/ o-ring maintenance at the end of every day of diving.

I then seal, initiate vacuum, set-up and check function under ~8mmHg vacuum pressure.

It takes me approximately 3-5 squeezes of the MiniVac handle to get from ~5mmHg to ~8mmHg. (More squeezes needed with a 230mm dome, fewer with a 105 port.)

Once complete, I let my whole system sit (under vacuum) until the next day of diving.

If there is still a green light showing in the morning, I feel comfortable that my risk of a leak is low and I proceed with the dive.

 

I used to check the "reading" in the morning, but found, even in tropical climates with high variations in overnight temps (sometimes kept in over AC camera rooms, some open air) there was usually zero to <~1mm variation in 8hrs.

What I did find is I was more likely to lose vacuum by checking the reading, and the reason I no longer "verify" the green light with a reading.

I do similar to what you are doing. Except that I turn off the sensor before I sleep. Next morning, I turn it on again. One last check on the camera. Then pump it up again. It might be repeated. But sometimes I have the unfortunate time that the battery ran out on me.

[ChrigelKarrer 52]

On my Nauticam LX-100 houisng i use 3 pumps more when the green light comes on.
That worked untill now perfectly.

 

My Hugyfot D800 housing need some more electric pump time, had it twice that housing showed a pressure drop and alarm came on,
but only when diving in cold water.

Chris

[ChrisRoss 150]

I think everyone is worrying too much about the issue. At least with the Nauticam pump, the pump is not that efficient as the plunger is quite a loose fit in the barrel, this means as the pressure in the housing gets lower there will be more leakage. Out of interest I did some rough estimates on how much vacuum should be developed with each pump stroke with the ideal gas law and the pump being 100% efficient. I found that for an approximation of my housing assuming a volume of 1.5 litres and the pump taking 44 cubic cm on each stroke that it took 6 strokes to get to 0.1 bar vacuum. In practice it takes me 8 strokes to go green so I would guess it might be developing 0.1 bar in the housing, possibly less. A few extra pumps won't do much as each pump stroke is a constant volume and as the pressure reduces it removes less and less air and the pump becomes more inefficient.

 

0.1 bar is more than enough to do the job as at that pressure with my Oly EM-1 MkII housing the pressure difference provides a force of 20-25kg keeping the back door closed. A DSLR may be double that due to the larger surface area of the door. I would be surprised if any system achieved actually 0.3 bar vacuum at the green light.

 

The point of the vacuum system is twofold. it allows a tightness test and it preloads the o-rings. O-rings must be loaded to seal . The test you are interested in is an air leak, air will flow at a significantly higher flowrate ( approx 40x volumetric flowrate) through any opening than will water. If you pump more air out the pressure differential increases and the leakage rate increases. The velocity of gas through the leak path is proportional to pressure differential squared , so you will have a higher leak rate at higher vacuum. As long as you don't go nuts when pumping down you'll be fine I think.

 

But the leak path through a hair sitting across an o-ring is pretty small so leave your housing pumped down for a decent amount of time

Edited April 7, 2018 by ChrisRoss

[thetrickster 328]

Thanks Ryan,

 

The one time I've seen it happen, I definitely didn't have a leak. Housing had sat for hours with a green light before getting in the water, and changed to yellow as soon as it chilled off on entry. Put it port down above my head on descent with no sign of water. The inside was bone dry after opening after over an hour in the water.

 

Bevan

 

I've had exactly the same thing. Green light for hours, do before I leave for the dive (around 7am) - dive time around 11am - still green. Hit the water and the amber light comes on. (the water temp is 15-16'c - air temp high 20's)

[tangfish 7]

 

I've had exactly the same thing. Green light for hours, do before I leave for the dive (around 7am) - dive time around 11am - still green. Hit the water and the amber light comes on. (the water temp is 15-16'c - air temp high 20's)

 

Just experienced the same as trickster and Bevan. The strange thing is, why does getting into water that's cooler than the air temperature cause this to happen? I would think that environmental cooling would enhance, not reduce the partial vacuum inside the housing. Oh well, gave me a nice scare, and prevented a blue ring photo!

Edited February 19, 2019 by tangfish

[ChrisRoss 150]

Cooler water will cause the pressure inside to drop, but the housing electronics attempt to compensate for that - the only thing I can think of is that this compensation may not be exact and it's enough to trigger the alarm as you are too close to the trigger point. Does it come on straight away or after you reach a certain depth?

 

How many pumps do you make after the green light? I generally make three pumps after the light first goes green and find the light stays green in the water. As I noted above I do not think the extra vacuum will be an issue, one because it it is not that much lower and two is that air leaks faster than water. If the light stays green for an hour or two the housing is tight and not going to leak. The only time the extra pumps might be a concern is if you jump into the water 5 minutes after pumping it down.

[Interceptor121 707]

 

Just experienced the same as trickster and Bevan. The strange thing is, why does getting into water that's cooler than the air temperature cause this to happen? I would think that environmental cooling would enhance, not reduce the partial vacuum inside the housing. Oh well, gave me a nice scare, and prevented a blue ring photo!

 

I think 4 degrees is a very limited range to really create any meaningful effect. Assuming that the volume is fixed 4 degrees are 3.8% of pressure change which is not something the temperature monitor would handle easily

 

There is one situation that can generate false positives and cannot be handled by any system which is when you prepare the housing in a very cold environment possibly an air conditioned room and the you go in warmer water this can generate up to 10% change of pressure and it will generate a false positive. So in general it is not a good idea to have a significant delta temperature between the preparation room and the water what would be ideal is to have very dry environment at the same temperature

 

Even if the water is slightly cooler especially if you take video there is a lot of heat generated in the housing that is far more important than the cooler water

 

So if you have the alert either you have a slow leak or a significant delta temperature between preparation and operating temperature of the camera

[ChrisRoss 150]

Even a 10° change in temperature is actually only a 3% pressure change. the pressure change is proportional to absolute temperature in kelvin so 20°C = 293K and 30°C = 303K If you start at 1 bar absolute the new pressure on heating 10° is 1.03 bar. (P2 = P1 x T2/T1). If you reach 0.1 bar vacuum when you pump down which is 0.9 bar absolute the pressure would change to 0.93 bar when heated 10°C. (Kelvin = °C + 273)

 

The problem could be simple. Presumably the system as it goes from blue through yellow to green is in a state where it is monitoring pressure and reporting that through LED colour and when it reaches target vacuum switches to a different state where it is monitoring pressure and temperature and is ready to alarm when it detects a change which can't be accounted for. When it does this the system alarms and is supposed to show red. It is quite simple to account for a 10° change with the ideal gas laws. Even a 20° change should not be a problem .

 

If you watch what happens when pumping it goes yellow and often flickers green- yellow for one or two strokes. The fact people are reporting the light returns to yellow indicates to me this is the case. If it detects an actual loss of vacuum or air/water leaking in the LED should flash red.

 

I always give it 3 pumps after I first get solid green and have never had this issue. As Is stated in my post above I believe people are over thinking this - air leaks in at a higher rate than water so pump it down and leave your housing sit for an extended period and you will be fine.

Edited February 21, 2019 by ChrisRoss

[String 17]

A few observations with mine.

 

I often prepare in a 20c room then dive in water 28 to 31c after that.

I also sometimes have the housing (accidentally) in direct sun in the tropics.

I've never had the vacuum fail or a warning when going to or from these environments.

 

It is very sensitive though. It picked up a hair on an O ring in about 20 mins and triggered after a few hours when my electrically connected ikelite strobe minus the battery (which was charging) created a tiny leak path through the cable and strobe.

 

So I think the circuit may well be temperature compensated or similar. It seems to behave with environmental changes but still very sensitive to actual leaks.

 

Sent from my BTV-DL09 using Tapatalk

[tursiops 81]

I expect when the housing hits cold water it shrinks slightly, so the pressure inside increases slightly...same amount of gas in a smaller volume.