Re: [PSUBS-MAILIST] Pressure air drive.

["Herve" <caribsub@coqui.net>]

I hope now everybody understands how devastating can be the acts of
irresponsibles dealing with uninspected, outrated, or uncertified equipment.
And how important it is to follow requirements guidelines and advises. This
poor guy lost his legs for refilling re-painted defective tanks because
somebody tried to save a few bucks at somebody else expense.
----- Original Message -----
From: "Mark Steed" <plutomark@mail.astate.edu>
To: <personal_submersibles@psubs.org>
Sent: Thursday, January 09, 2003 1:22 PM
Subject: Re: [PSUBS-MAILIST] Pressure air drive.


> Herve: Excellent stuff. Thanks. One of the most dangerous aspects of SCUBA
cylinders that I am familiar with is high heat. Anytime aluminum cylinders
are exposed to high heat, they turn extremely brittle. Several years ago
when I was diving a lot more, it became the rage to have the wildest paint
scheme on SCUBA tanks. One method was to coat the tank with a particular
paint that required it to be baked for a time. A set of twin aluminum
cylinders were treated this way and upon their refill at the dive shop
compressor, they exploded. I did not know the dive shop operator but heard
about it later. When the tanks blew, they removed both his legs and
destroyed the shop. For a long time, no one would even think about filling
re-painted aluminum cylinders unless they knew their history. Steel
cylinders, I'm sure, are much safer.This has been several years ago and I
assume nothing has changed. Thought I would pass this along. It is something
I have remembered for a long time.  Bees!
> t !
> regards, Mark Steed
>
>
> ---------- Original Message ----------------------------------
> From: "Herve" <caribsub@coqui.net>
> Reply-To: personal_submersibles@psubs.org
> Date:  Thu, 9 Jan 2003 13:42:29 -0400
>
> >Yes all scuba tanks have different sizes in the US, a100cuft aluminium
tank
> >(3000 psi) is bigger than a steel 100 cuft tank (3500 psi), expended air
is
> >the same, but volume of compressed air is different depending of the
> >pressure.
> >
> >It is prohibited to refill breathing air tanks from industrial
compressor,
> >or air shop compressors. Scuba HP compressors are designed to fill up
> >cylinders with high pressure with no moisture or contaminated gas.
> >When you compress air, temp goes up and oil or grease residuts, if any,
but
> >present in industrial comp can burn and produce CO, which is odorless.
> >Moisture in tanks creates oxydations inside, even in a aluminium tank and
> >weakens the walls.
> >In 1981 during my first scuba dive in the NAVY, 2 experienced divers on
> >another task died because of that. It was a n old compressor, and
somebody
> >reversed a set of filters, which produced CO due to the high temperature.
> >They both lost conscience and drawned and never forgot that. So a good
> >advise....  use dedicated compressors to refill tanks and other life
support
> >air sytems, and leave shop air compressors for air tools.
> >Herve
> >----- Original Message -----
> >From: "Carsten Standfuss" <MerlinSub@t-online.de>
> >To: <personal_submersibles@psubs.org>
> >Sent: Thursday, January 09, 2003 12:54 PM
> >Subject: Re: [PSUBS-MAILIST] Pressure air drive.
> >
> >
> >> I think there is a missunderstanding .. ?
> >>
> >> The motor needs 3 cfm means : "A volume of air of 3 cf in one minute
> >> at normal atmospheric pressure.."
> >>
> >> That means in other words the air consuption of the engine is given as
> >> expanded air - for example on the surface after using the motor and
> >> collected in a bag..
> >>
> >> The pressure figure of 90 psi ist just the differnce  between the motor
> >> inlet and the motor outlet..
> >>
> >> If you have a 220 cf tank and a 3 cfm air consumption
> >> the time figue is 220 cf air / 3 cfm = 73 Minutes (on surface only)
> >> and it doesn't matter if the pressure differntial the motor
> >> need is 9 or 90 or 900 PSI..
> >> The Psi figure is only relevant if the boat dives deeper
> >> because the rest amout of air not useable in the tank will be more in
> >> greater deeps. The motor will stop running at least if the internal
tank
> >> rest pressure and the pressure outside the boat is equal.
> >>
> >> In metric figures:
> >>
> >> 1cf is equal to 28,3 liter
> >>
> >> Scuba Tank size 10 Liters in german means
> >> a scuba tank of 10 liter (size is 10/28,3 = 0,3533 cf)
> >> but with a pressure of 225 atmosp. (bar)
> >> = 2250 Liter (80cf) expanded air on the surface pressure.
> >>
> >> and yes that is equal to a 80 cf tank in your imperial language..
> >>
> >> a 80 cf tank has a run time of 80/3 = about 27 minutes
> >>
> >> Thats funny : we give allways the real size of the tank..
> >> you can fill 10 Liters of water in - but 2250 Liter of compressed air..
> >> But your language give the volume of the air inside if the air
> >> is expanded to a standard atmosphere - right ?
> >> This indicates that you use normal tanks with differnt
> >> max.pressures ?
> >> We here use all the time 200 bar tanks - which are today normaly
> >> filled up to 225 bar..
> >>
> >> regards Carsten
> >>
> >> jbarlow@bjservices.ca schrieb:
> >> >
> >> > The motor needs 3 cfm @ 90 psi and expels approximately  (3*90 / 14.7
> >> > (depending on where you live ... presumably sea level if you are in a
> >> > submarine, but if you dive in Lake Minnewanka* @ high altitude then
> >> > presumably you could get more out of the air supply)) = 18.3 cfm
> >> > ...therefore  220 cubic feet / 18.3 = 11.9 minutes.
> >> >
> >> > 220 cfm doesn't equal 2250 litres The original assumption was for a
std
> >> > scuba tank.  (Note: 220 cfm is one very large scuba tank)
> >> > 2250 litres equals 80 cubic feet which is a std scuba tank.
> >> >
> >> > Also the assumption was for 2 motors or 6 cfm @ 90 psi which makes
the
> >12
> >> > minutes actually 6 minutes.  Actually less because air isn't an ideal
> >gas.
> >> >
> >> > Unless you heat the air after (or before I guess) regulating it from
the
> >> > high pressure to add back in the energy lost due to the cooling
effect
> >of
> >> > expansion.
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >   *Minnewanka, Lake (mi-ni-WAHNG-kuh) SW Alta., Canada, near B.C.
> >border, in Rocky Mts., in Banff
> >> >   Natl. Park, 6 mi/10 km NE of Banff, at foot of Mts. Aylmer and
> >Girouard; 12 mi/19 km long, 1
> >> >   mi/1.6 km wide. Elev. 4,769 ft/1,454 m.
> >> >
> >> >
> >> >
> >> >
> >> > Jay.
> >> >
> >> >
> >> >                       "Pierre Poulin"
> >> >                       <pipo305@hotmail.com>             To:
> >personal_submersibles@psubs.org
> >> >                       Sent by:                          cc:
> >> >                       owner-personal_submersible        Subject:  Re:
> >[PSUBS-MAILIST] Pressure air drive.
> >> >                       s@psubs.org
> >> >
> >> >
> >> >                       08/01/2003 06:59 PM
> >> >                       Please respond to
> >> >                       personal_submersibles
> >> >
> >> >
> >> >
> >> > The math is simple:
> >> >
> >> > one tank of 220 cubic foot. divided by 3cubic foot/minute = 73
minutes
> >of
> >> > non-stop full throttle operation. So air reserve doesn't seem like an
> >issue
> >> >
> >> > to me.
> >> >
> >> > My question is more the 25000 rpm and 0.6 HP. Would that be enough
for
> >> > moving my 1092 lbs ambient sub? And there is also the propeller
design
> >> > consideration (which I'm no expert)
> >> >
> >> > So, What do you think about RPM and HP?
> >> >
> >> > Pierre
> >> >
> >> > >From: Coalbunny <coalbunny@vcn.com>
> >> > >Reply-To: personal_submersibles@psubs.org
> >> > >To: personal_submersibles@psubs.org
> >> > >Subject: Re: [PSUBS-MAILIST] Pressure air drive.
> >> > >Date: Wed, 08 Jan 2003 16:52:29 -0700
> >> > >
> >> > >And that would explain why WW2 torps had a range of less than a
mile.
> >> > >NOW I understand.
> >> > >Thanks Jay!
> >> > >Carl
> >> > >
> >> > >
> >> > >jbarlow@bjservices.ca wrote:
> >> > > >
> >> > > > 3 cubic feet per min at 90 psi
> >> > > >
> >> > > > If air is ideal gas then P1 x V1 = P2 x V2
> >> > > >
> >> > > > 3000 psi X .353 ft3 = 90 psi x V2
> >> > > >
> >> > > > V2 = 11.76 ft3 @ 90 psi
> >> > > >
> >> > > > 11.76 / 6 = 1.96  min.
> >> > > >
> >> > > > The volume gets worse by the head of water (15 psi per 32 feet)
and
> >> > also
> >> > > > the motors lose power as then can't fully expand the air back to
> >> > > > atmospheric to regain the stored energy.  You could overcome this
by
> >> > > > feeding the motor ever increasing pressure air (measured inside
your
> >> > >boat)
> >> > > > as you dove deeper.  that is regulating it down less, to regain
the
> >> > >power
> >> > > > loss, but that again would shorten your range.  320 feet is about
> >150
> >> > >psi
> >> > > > so now you need to feed the motors 90 + 150 = 140 psi to get .6
hp
> >and
> >> > >the
> >> > > > 1.96 minutes becomes 1.26 minutes.  Based on the 10 litre scuba
> >bottle.
> >> > > > Obviously one would need bottled gas cylinders.
> >> > > >
> >> > > > about 1.5 min per 10 litre bottle @ 10 atm. depth.
> >> > > >
> >> > > > Still a sound concept.  If you have to use shop air (easy and
cheap
> >> > > > compressors) then i think it is not workable.  If you have access
to
> >> > > > 3000-4000 psi compressors then it should work fine for short
> >duration
> >> > >use.
> >> > > > For an occasional use would be great as it has no shelf life.
> >> > > >
> >> > > > Jay.
> >> > > >
> >> > > >
> >> > > >                       MerlinSub@t-online.de
> >> > > >                       (Carsten Standfuss)               To:
> >> > >personal_submersibles@psubs.org
> >> > > >                       Sent by:                          cc:
> >> > > >                       owner-personal_submersible        Subject:
> >Re:
> >> > >[PSUBS-MAILIST] Pressure air drive.
> >> > > >                       s@psubs.org
> >> > > >
> >> > > >
> >> > > >                       08/01/2003 10:47 AM
> >> > > >                       Please respond to
> >> > > >                       personal_submersibles
> >> > > >
> >> > > >
> >> > > >
> >> > > > Pierre Poulin schrieb:
> >> > > > >
> >> > > > > Hi,
> >> > > > >
> >> > > > > I've check some air grinders that could be transformed into
motor.
> >> > > > >
> >> > > > > Free speed: 25000 rpm
> >> > > > > - Operation pressure: 90 psi
> >> > > > > - 0.6 HP
> >> > > > > - Air consumption: 3 cfm
> >> > > > > - Weight: 1.5 lb
> >> > > > >
> >> > > > > What do you think about that?
> >> > > > >
> >> > > > > Pierre
> >> > > > >
> >> > > >
> >> > > > Hmm.. 3 cfm means cubif -foot- minute ?
> >> > > > than it is
> >> > > > are equal (sorry I think in metric..)
> >> > > > to 3 x 0,3048 x 0,3048 x 0,3048 m = 3 x 0,028 m3 or 84 Liter
> >> > > >
> >> > > > if we estimate that the boat need two engines of 0,6 hp we need
> >> > > > 2 x 84 liter = 168 Liter a minute.
> >> > > >
> >> > > > A normal scuba bottle has 10 Liters at 225 bars = 2250 Liters
> >> > > > air and run the drive just 2250/168 = 13 Minutes
> >> > > >
> >> > > > A yard size bootle for weld gas has 50 liter and is 1,5 m (4,9
feet)
> >> > > > high with a diameter of 280 mm (11 inch) runs about
> >> > > > 5 times longer = 65 minutes..
> >> > > >
> >> > > > Two tanks of 50 Liters gives you 2 hours and 10 minutes..
> >> > > > Not so bad - Batterys has to be replace after some years -
> >> > > > pressure bottles not - and a 50 Liter industrial one is about
> >> > > > 300 Dollar new and maybe cost the half if you purchase a used
one.
> >> > > >
> >> > > > Problems:
> >> > > > - to get an engine made from seawater resistant material
> >> > > > - the noise ?  -> no fish around the boat
> >> > > > - the air bubbles all the time ? -> no fish around the boat
> >> > > >
> >> > > > Most problem is maybe that high pressure scuba compressor
> >> > > > is mcuh more expensive than a battery charger.. :-(
> >> > > > But for peoples which are allready scuba divers - and have
allready
> >> > > > a compressor - a solution.
> >> > > >
> >> > > > Carsten
> >> > >
> >> > >--
> >> > >"You delight not in a city's seven or seventy wonders, but in an
answer
> >> > >it gives to a question of yours, or the question it asks you,
forcing
> >> > >you to answer, like Thebes through the mouth of the Sphinx." --
Kublai
> >> > >Khan
> >> >
> >> > _________________________________________________________________
> >> > MSN Search, le moteur de recherche qui pense comme vous !
> >> > http://search.msn.fr/worldwide.asp
> >>
> >>
> >>
> >
> >
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