Negative test.

Nick uk.

As i'm going to get to the bottom of the leaky ADV, sooner or later..... I was wondering how long you guys can get your units to hold a negative preasure, at the minute i'm pushing my look at two minutes, but have never had more than 45mins on a good day, whats the norm for you guys. Give me an idea of what to be heading for.

Cheers, Nick.

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Drmike

I test for prob less than 1 min whilst gearing up before every dive. If it holds a good strong vacuum for that 1 min I dive.

During any dive the loop is at ambient pressure so I dont see the need to get too paranoid (I read reports of some people worrying when they cant keep a neg overnight!)

A leaky ADV though will cause you to waste a lot of O2.

But to answer your question,

My inspiration = 3 mins (leak in T piece seal from new)
My MK15.5 = 12hr+

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Phil Ennis

Hi Nick,

My experience both with the Classic and my Vision is that if the unit is dry, ie has not been dived for a week or two, then it will hold a neg for about 10 mins. There is still a vacum in the loop, but the hoses have popped back out which is fine. If the unit is moist, ie dived within the last couple of days then it holds a neg with the hoses still crushed for longer than I have tested.

What has happened sometimes is that I do the neg, check then forget to open the mouthpiece and the neg is still held with the hoses crushed over 12 hrs later.

I don't relly know what the wet and dry bit is telling me really, it is just my experience with the two units.

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decoweenie

8 years, 10+ different rigs, best max negative time is only a couple of minutes. Is it me ?

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seafox

Nick, on the average I will test both neg and pos pressure for at least 10 mins (each), at the beginning of each day of diving.

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edster

I've found that the air gets in around the mouth piece, and so if its freshly greased 20 mins is easy, if not its 2 or 3... but now I know that I'm less paranoid!

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Mark Chase

Overnight no problem with the YBOD mouthpiece about 20 seconds with the KISS mouthpiece

Didnt Gordon say somthing about dont put units in Neg for too long as it screws the diaghpram in the ADV? Does this affect YBOD's or is it a KISS specific problem.

ATB

Mark Chase

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Beanie

It's a KISS problem but it could also effect YBODs
If it holds for 2-3 mins it will be fine its when it doesn't hold at all that its a problem.
Also it should hold a pos aswell

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nigelh

Well that's the reason I won't leave my YBOD with a Bob ADV on negative for long.
I just picture what it is doing to that LPO diaphram, wince and realise I'm not that mechanically insensitive so it gets let off in about 30 seconds.

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