[PSUBS-MAILIST] Over Pressure Valve

Fri Jun 19 15:58:08 EDT 2015

John, I hadn't given much thought lately  to how the Big Boys handle it.  
I've planned to have a small, onboard  compressor, but its purpose is to 
create under-pressure to seal the domes prior  to diving.  It's not large enough 
to charge the tanks.  I'm depending  on a portable compressor dockside or 
on the support boat for that.  A  snorkel would be nice even if it extends 
just two feet above the hatch or  dome.  Looking forward to the update on your 
65-footer at the  convention.

Hank, that's definitely a sweet setup you have on Gamma.   The compressor 
recharged the tanks much more quickly than I expected.  I  don't recall how 
low you let them get before recharging.  I don't expect to  have room 
onboard, and the heat generated would be something of a negative in  semitropical 
conditions.

I wish I knew what the pressure differential was that Captain  K. 
experienced.  Apparently it was small enough that he wasn't aware of it  and yet 
significant enough to convert his coming tower into a personnel launch  tube.  
If the air pressure inside your sub rose to 20 psi or  about 1.33 atm, you 
would reach equal pressure when you got within 11 feet of  the surface.  Any 
depth greater than that and the outside pressure would  still be greater than 
the inside pressure (no OP).  The point being that  you would have to have 
a lot of excess interior pressure to experience OP at a  significant depth.  
Wouldn't your ears tell you if you got as high as 20  psi?  Monitoring and 
alarm systems are a must.

Jim

Personally I think an onboard compressor is a much safer option than an  
over pressure valve.  There are multiple safety benefits to an onboard  
compressor, over pressure being the biggy.  With a compressor you can get  rid of 
the pressure without surfacing and trying to control a perfect  ascent.  
With the OPV you have to surface a bit and let air out and wait  then surface 
more and wait and so on. You can't just surface and hope the valve  keeps up 
with the demand. This is more important for subs with large  domes.
The next benefit to a compressor is, if you lost all your air, you  surface 
by dropping your weight.  In my case the weight is small and I  would also 
drop the thruster and tail assembly.  Still, not much sub out of  the water. 
 With the compressor, I can open my vent valve in the hatch and  use the 
compressor to fill the ballast  tanks.
Hank
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In a message dated 6/19/2015 12:35:49 P.M. Central Daylight Time,  
personal_submersibles at psubs.org writes:

Hi  Jim:

On the boat if their was an positive pressure while submerged at  depth we 
started the air compressor and charge the air banks. The other option  was 
to raise the snorkel to equalize before opening the hatch.

John  K.
(203) 414-1000

Sent from my iPhone

> On Jun 19, 2015,  at 3:07 AM, via Personal_Submersibles 
<personal_submersibles at psubs.org>  wrote:
> 
> Jim,
> 
> Thanks for the mental diagram,  that helps imensely. Does any one know 
how the big boys, navy subs, deal with  over pressure? Has any one had their 
OP valve open at depth and if so how much  water came in?
> 
> Keith T
> 
> via  Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>  
>> Keith,
>> 
>> Sorry, I just got home.  I  was hoping Alec and some  others with more 
>> experience than I  have would chime in as I see has now  happened.  
There have  
>> been some good discussions on OP valves in the  past.   I think some 
have 
>> installed a T (on its side) inside the sub  so  the air enters the 
horizontal 
>> portion, and any water  that comes in  goes down to a small trap or into 
a tube 
>> that  leads to a reservoir.   Others just use a rag to catch the small  
amount 
>> of water.
>> 
>> Alec, does the OP on  the exterior of Snoopy point downward  after it 
exits 
>> at the  top?
>> 
>> We've also discussed having an air pressure  gauge or altimeter  set to 
zero 
>> (1 atm) before diving.   If it indicates any pressure above  that level 
at 
>> anytime  during your dive, you'll know you'll have an over pressure  
situation  
>> to deal with as you surface and you'll have an indication of  how  
severe 
>> that will be.  We've also discussed various  things that could cause  an 
over 
>> pressure  condition.
>> 
>> Best regards,
>> Jim
>>  
>> 
>> In a message dated 6/18/2015 7:09:19 P.M. Central  Daylight Time,  
>> personal_submersibles at psubs.org  writes:
>> 
>> If it opens when submerged, it is because air  is on the way out,  and 
that 
>> prevents water from coming in.  Its like blowing through your nose  
>> underwater, your nose is  open but if you're blowing, you don't get 
water in  your 
>>  lungs.  
>> 
>> 
>> Certainly you do get a  little water in if you push the valve open  
manually 
>> while  submerged, as a test. Or a few drops if you do so when surfaced  
to  
>> equalize, as the valve is all wet. But its nothing  much.
>> 
>> 
>> 
>> Best,
>>  
>> Alec
>> 
>> 
>> 
>> On Thu,  Jun 18, 2015 at 7:19 PM, Ken Martindale via  
Personal_Submersibles  
>> <_personal_submersibles at psubs.org_  
(mailto:personal_submersibles at psubs.org) 
>>> wrote:
>>  
>> TEST!!!
>> 
>> -----Original   Message-----
>> From: Personal_Submersibles 
>>  [mailto:_personal_submersibles-bounces at psubs.org_  
(mailto:personal_submersibles-bounces at psubs.org) ]  On Behalf Of via  
>>  Personal_Submersib
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