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Re: [PSUBS-MAILIST] Pressure air drive.
You must gear down the airmotor. 25000rpm is too fast for any prop. I think
that the 73 minutes might be generous, but not by that much. I think the only
real flaw in that calc is that you have to subtract a few hundred psi from the
tank, which affects capacity, to allow for the water pressure. If Pierre is running
an ambient pressure sub then he has to subtract very little, and this becomes even
more practical. Those gear-reduced air motors I was quoting as 3hp at 60cfm were
not a bad option. It could be done more efficiently, but that is good enough.
Warren.
> I think that would work only in circumstances of consant force.
> Unfortunately the faster you go, the more force therefore the mosr air
> needed. I thinkt hat CA is a good idea, but the 73 minutes is kinda
> pushing it, isn't it?
> Carl
>
>
> Pierre Poulin wrote:
> >
> > 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
>
> --
> "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
--
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