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Re: [PSUBS-MAILIST] Pressure air drive.
You have to supply the air motor at approx 6 atm. (90 psi / 14.7 psi)
from your 10 (Carsten's Number) atm tank only allowing you to draw your
tank down to 6 atm. (using 4/10 of capacity) Further subtract the number
of atm you are deep.[see below]* Doesn't matter ambient or wet sub ,
motor inside or outside, because ultimately the air must be expelled
outside. Otherwise internal pressure will rise as if you had opened the
valve from the 220 cf @ 3 ksi tank to the inside. Then you probably have
to decompress before you get out depending of course on the internal volume
of your sub. On the plus side this would increase the safe working depth
of the sub though.
The motor would work at less than 90 psi (6 atm supply) but the hp produced
would drop also. At the 2-1 atm pressure drop (where half of your stored
cubic feet of air come from, half of the "73 min"), presuming you are on or
near the surface, you would get virtually no power out of a motor. Try
your die grinder with your shop air compressor at 30 psi.
Or did you mean 220 cubic feet at 10 atm.?
ie a tank 6' x 6' x 6' inside (or outside the pressure hull would make
more sense actually) the sub (6 x 6 x 6 = 216 cubic feet)?
That would give you:
220 cf X 10 atm / 6 atm = 366 cf / 3 cfm or 122 minutes of supply at full
power one motor ( or 61 minutes for two motors as suggested by Carsten)
Then Capacity isn't bad but its a pretty big tank.
* If you are 10 atm deep then 10-10 equals 0. If you opened a 10 atm tank
to outside at 10 atm depth then theoretically no air would escape. At 11
atm depth then water flows into tank, and the air drive doesn't work.
Right? 32 feet = 1 atm so 10 atm = 320', which isn't extremely deep. And
there is only half capacity at 32' deep, which is pretty shallow.
[I made an error before. 90 psi + 150 psi = 240 psi not 140 psi. Time
becomes 45 seconds from 1.26 minutes] from normal 80 cubic foot (at
Standard Temperature and Pressure) scuba cylinder.
As before I suspect you need minimum a 25:1 reduction gearbox. More likely
50:1 (500 rpm prop speed, still high I think but I know virtually nothing
about propellers)
I still like the concept though. Not having batteries to go bad after
years of non-use is a good thing. And if you used XP (extra capacity)
Nitrogen cylinders that you simply had filled, then you don't need to buy a
4000 psi compressor and for occaisional use it would be much more
economical.
The 3 hp motor makes more sense power wise but needs a ten times bigger
supply tank. ie 13' x 13' x 13' tank.
What a lovely mix of units above, eh?
Jay.
Is someone going to call "Dead Horse" yet?
"Warrend Greenway"
<dub@linuxmail.org> To: personal_submersibles@psubs.org
Sent by: cc:
owner-personal_submersible Subject: Re: [PSUBS-MAILIST] Pressure air drive.
s@psubs.org
08/01/2003 09:36 PM
Please respond to
personal_submersibles
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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