Quote: (Originally Posted by
schford)
I am probably being slow
I keep on seeing signs that say "Slow Children", do you remember one of these near where you grew up?
Quote: (Originally Posted by
mverick)
The air has to pass through the scrubber material. Giving a very slight back pressure. The differential is there. But it's minimal...
Quote: (Originally Posted by
UWSojourner)
The pressure will be very small. The pressure of the predive test itself will be large relative to the actual dive pressure. If the cells are that delicate I would think the predive test would provide some possibility for damaging the cells.
Quote: (Originally Posted by
silent running)
Hi Ron, I've never seen a the inside of a Meg head, so I don't know exactly what it looks like, but do you know why the sensors are mounted in such a way as to have this p differential accross them? What is the design advantage of having them mounted this way?
If there's 2 steps in the setup to check the carriage seal, then ISC are aware of the potential problem, even if it is not so likely to occur. Just wondering about the thinking behind their placement. Thanks, -Andy
Quote: (Originally Posted by
wedivebc)
Actually the pressure difference is only the pressure drop across the scubber which is minimal. The +/- check was originally designed to check the o-ring seal in the sensor housing and in earlier models the one way valve on the water drain (later removed by ISC). I don't think it was designed to be a sensor integrity check and frankly I am not sure it is a very common problem other than DR MIke's experience I have not heard of it before.
I completely agree the pressure difference will be very small most of the time during a dive - however if you place 100mm (4 inches for you colonials) of water in the bottom of the canister and go vertical, the WOB increases enormously, at that point anyone with strong and committed lungs would be in a position to damage cells.
During MOD1 I was told how to recover from a flood / remove water from the can.. so I went ahead with the exercise and put many liters or water in the can.
During this experiment I was interested to note the different sounds and WOB that the water was creating, I got it to the point that in a vertical position it was quite hard to suck gas through.
I then proceeded to get most of the water out which I was very please with and finished the dive, this was the last exercise of the last dive and I thought that the reason I lost one cell was due to it getting salt water on it. – Perhaps the real reason was the difference in pressure was too much for that 1 of the 3 cells.
Perhaps if I was able to suck a golf ball through a hose pipe then I would have damaged more than one cell.
Quote: (Originally Posted by
wedivebc)
I knew this girl in Halifax once who could suck start a diesel engine but in most cases the pressure involved is pretty low.
2 cells for sure, would you let her test your carriage assembly?
Quote: (Originally Posted by
Decodiver)
Yeah and I knew a bird who could suck the chrome off a bumper!!
All 3 cells. There is no way that would be safe check.
I thought that the design was based around using a radial scrubber where the flooding becomes less of an issue from a pressure perspective - but it still would not explain how you are supposed to test pressure across something that is not designed to take any pressure.