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Re: [PSUBS-MAILIST] Pressure air drive.
Bingo!
Carl
jbarlow@bjservices.ca wrote:
>
> 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 !
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> >
> > --
> > "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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--
"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