Vacuum test - how much to suck?

I have a Nauticam housing with their vacuum system. For a morning dive, I usually seal my camera the night before, and if the light is still green in the morning, I'm happy to dive.

A few days ago I installed a 45º view finder, and I'm off on a dusk dive this evening. In the morning I sealed and vacuumed my housing. At lunch, the light was fluttering between orange and green.

I've opened it and inspected the port, viewfinder and main o-rings, re-sealed and re-vacuumed it.

But I'm not sure if I vacuumed it enough initially, and if the orange flicker was just the sensor adjusting to temperature fluctuations. My central heating kicks on at 6:30 am, and I sealed my housing around 8:30am, while the house was reasonably warm. Heating turns off again at 9am, so at lunch time the temp has dropped a few degrees.

When I pumped the vacuum, I stopped mid-stroke on the pump just as the light turned green. Is this sufficient, or should I give it a little bit more suck after the light goes green to allow for temperature fluctuations?

actually we just give it 2 to 3 more strokes to ensure that it is a full vacuum, bcos the trigger for the alarm is not at a max full vacuum.... bcos we cant really achieve that level of vacuum which is void of all air in our camera housing... 

thus it is considered safe to give it abit more strokes...

I don't have the Nauticam system but do use the Vivid Sentinel. With that system once a solid green indication appears, I add two more pumps. This seems to work pretty well.

Getting into the gass laws again. Warmer would mean higher pressure. Colder less pressure so 'more' vacuum. So if the circuitry measures the pressure, the housing cooling down should not give a false warning, the housing warming up could give a false warning.

if the nauticam circuitry is temperature compensated (and this seems to indicate it does), then you might have a slow leak.

View archived post in: Nauticam Vacuum valve - how much vacuum?

PS: I also use the sentinel. I've had false warnings with the older version, in a warm pool.

Nauticam is temperature compensated. Once le led turns green I add 1 or 2 more pumps.

Thanks for all your replies.

I resealed the housing and re-vac'd it - this time when it turned green I finished the pump and did one more. My dive was about 6hrs later, and still green. One hour dive, max depth 7m, no leaks.

3 hours ago, froop said:

Thanks for all your replies.

I resealed the housing and re-vac'd it - this time when it turned green I finished the pump and did one more. My dive was about 6hrs later, and still green. One hour dive, max depth 7m, no leaks.

Very good news!

NA-XT3 housing, with both, 40mm and 110mm ports. Usually vacuum 1-2 hour before diving, just until light turns green (12-13 pumps). Normally Mediterranean, so water themperature is 15-22° Celsius, air themperature 18-30° Celsius. There can be a big difference between air and water, last weekend 33° air vs 17° water. No issues or false alarms until now. Perhaps 2-3 pumps just before going on board is a good advice I am going to adopt from now on. 

Best Regards 

There have been other posts on here from people who try to minimise the vacuum they apply thinking it will react faster to a leak or other reasons and they end up with a similar situation.  The temperature compensation might be included but if it is hovering right on the min vacuum it may not be accurate enough to fully compensate.  I always give it 2 more pumps after green first appears and it has never given me  a problem  If you want to be sure just leave the vacuum on for longer before jumping in - at least an hour is good if you can manage it.

I normally allow two extra pumps. I've left it on unopened for a day and held vacuum.

The more you over pump, the more away from the switch point you are. IF there was a small leak, it would take longer to leak up and activate the alarm. If you only just flip in to green and stop, you risk temperature variations that can change the pressure and trip the alarm. So a little bit over pumped would normally be required. Try it with one over pump and leave it for a few hours and see, if ok then when do it again when cold, let housing warm up a bit (pressure will rise slightly) and see if it trips. You are just seeing how sensitive it is, then you know.  

Always keep in mind, however small, there is always a small leak, it may take days to alarm but it is there. (that's just background info)

I’ve used both Vivid and Nauticam vacuum systems.  With both, two extra pumps has always worked perfectly.  
 

I’ve understood that vacuum alarms work on a relative basis, not absolute. That is, the internal vacuum only needs to drop a certain amount, not leak all the way up to ambient pressure.  Anyone know if this is the case?