[PSUBS-MAILIST] Over Pressure Valve

Fri Jun 19 21:39:07 EDT 2015

Hi Jim,as you were talking of pressures in a range outside ofthat of a normal barometer, it was assumed that you were talking about a normal pressure gauge reading & using standard vernacular.That's Jim Todd isn't it. I don't want to get too cheeky with the wrong person:)Cheers Alan
      From: via Personal_Submersibles <personal_submersibles at psubs.org>
 To: personal_submersibles at psubs.org 
 Sent: Saturday, June 20, 2015 12:52 PM
 Subject: Re: [PSUBS-MAILIST] Over Pressure Valve

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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