[PSUBS-MAILIST] Over Pressure Valve

Fri Jun 19 20:52:11 EDT 2015

Hi Alan,
I'm speaking in terms of absolute pressure.  That is,  pressure at the 
surface being 14.7 psi or 1 atm and water pressure at 33  feet deep being 2 atm. 
   I think you're speaking comparatively as  though air pressure at the 
surface were 0.0 psi.  Right?
Jim 

In a message dated 6/19/2015 4:46:04 P.M. Central Daylight Time,  
personal_submersibles at psubs.org writes:

Jim,
>>> 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. 
   No 40ft. 
Alan

____________________________________
 From: via Personal_Submersibles  <personal_submersibles at psubs.org>
To: personal_submersibles at psubs.org  
Sent: Saturday, June 20,  2015 7:58 AM
Subject: Re:  [PSUBS-MAILIST] Over Pressure Valve

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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