[PSUBS-MAILIST] bellows add

[Cliff Redus via Personal_Submersibles]

 FYI,  When I first setup life support system for the R300, I tried to implement a bellows add without the bellows by having the PLC monitor cabin pressure with an accurate barometric pressure sensor (700-1400mBar).  The ladder logic would trigger a O2 add when the cabin pressure dropped below a low pressure set point.  I found that the system did t work very well for my boat as my cabin pressure was not constant enough due to pressure build due to slow leak into the cabin or due to temperature swings.  I abandoned using cabin pressure to trigger O2 makeup and went to measuring the O2 concentration.  If the O2 concentration drops two percent below normal air concentration, I trigger O2 makeup at 4 times normal consumption rate until concentration increased to 1% above normal.  This approach worked way better for my boat.  I am planning on using the same technique in my next boat.


 

________________________________
 From: Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Monday, October 6, 2014 5:19 PM
Subject: Re: [PSUBS-MAILIST] bellows add
  


I agree Hank,
I think you should email Phil & warn him:)
I have thought that if there was an air leak in to the cabin the bellows add system
would stop adding O2. They have a manual system integrated into the bellows add
unit & a continual feed of O2 regardless of the belows. They would have O2 monitors
with set point alarms if the O2 % was too high or low but how they would address an
alarm issue I don't know.
I like Cliff's method of having a set volume flowing in (as per DW) & O2 addition generated
by O2 measurements opening an O2 solenoid valve via a PLC. This is similar to a
rebreather & James Cameron's system on the Deepsea Challenger.
Don't get me going on the coffee issue. I buy green beans & roast them. Would grow
them if we had the climate. 
My side of Auckland had power. Hugh lives on the Dark side.
Alan





________________________________
 From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
To: personal_submersibles at psubs.org 
Sent: Tuesday, October 7, 2014 10:07 AM
Subject: [PSUBS-MAILIST] bellows add
  

I have been pondering the idea of a bellows add system for Gamma.  I am not sure how the DW deals with pressure change due to temperature change.  When I am diving Gamma the temperature swing is huge causing a big negative pressure inside.  A bellows add system would be dumping O2 in like mad.  Does the DW have an automatic O2 over ride or an automatic air release to compensate. Does the pilot manually add air to avoid O2 build up.
When I surface after a dive without the scrubber or O2 feeding in, I have to open my hatch vent valve for what seems like forever to equalize the sub to open the hatch.  It is getting better with the air temps dropping.  I can't wait to go for a dive when it is snowing. 
Hank
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