[PSUBS-MAILIST] Over Pressure Valve
Alan James via Personal_Submersibles
personal_submersibles at psubs.org
Fri Jun 19 23:57:12 EDT 2015
OK, as a group, do we have to designate psig or psia to be on the same page.In some industries if there is no designation it is assumed to be psig, (gauge) whereasin other industries it is assumed to be psia (absolute). & we are using guages (psig)& barometers (that show a negative pressure relative to our 1 atm).Is their a nautical or submarine standard? Does anyone else have an opinion on this?Alan
From: via Personal_Submersibles <personal_submersibles at psubs.org>
To: personal_submersibles at psubs.org
Sent: Saturday, June 20, 2015 3:21 PM
Subject: Re: [PSUBS-MAILIST] Over Pressure Valve
Hi Alan,Cracking pressure only relates to the pressure differential from one side of the valve to the other. There's no relevance to absolute pressure.Jim In a message dated 6/19/2015 9:45:45 P.M. Central Daylight Time, personal_submersibles at psubs.org writes:
Hi Jim, it's a confusing way of looking at it. If I say that my overpressure valve has a 1psi cracking pressure, everyone knows what I am talking about. If I say it has a 15.7psi cracking pressure (1 atm + 1psi) everybody is going to think I am going to blow my dome off before I relieve pressure. You are Americanizing this too much & need to get back to basic Queens English. I'll have my pressure gauge set at 0 not 14.7 as it will confuse things. It's pretty wet here over the Winter. The last 2 years I've escaped to Thailand for Dental work & lots of snorkeling. There are some mind blowing snorkeling / diving spots there. p.s. Are your tyres feeling flat? :)
Alan
From: via Personal_Submersibles <personal_submersibles at psubs.org>
To: personal_submersibles at psubs.org
Sent: Saturday, June 20, 2015 1:58 PM
Subject: Re: [PSUBS-MAILIST] Over Pressure Valve
Yup, Alan, that's me. I'm using Psubs vernacular as in a 1ATM sub having an internal pressure equal to sea level pressure or 1ATM or 14.7 psi (absolute pressure). You're using the vernacular I use when I'm airing up the tires on my trailer and say I have 32 psi in the tire (tyre to you). In that conversation we're referring to differential or gauge pressure. Since your vessel is an ambient, I can where the confusion would come in. Now about you guys in NZ having winter in the middle of summer... JT In a message dated 6/19/2015 8:42:43 P.M. Central Daylight Time, personal_submersibles at psubs.org writes:
Hi Jim, as you were talking of pressures in a range outside of that 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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