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Re: [PSUBS-MAILIST] Pressure air drive.
Carsten,
Are you sure about the 3 cfm at 1atm? I am pretty serious about using the
air driven on my ambient sub in fresh water.
If the tooling is 3 cfm at 90 psi the difference between 73 minutes and
12 minutes of autonomy is really big!
Thank you very much!!
Pierre
>From: MerlinSub@t-online.de (Carsten Standfuss)
>Reply-To: personal_submersibles@psubs.org
>To: personal_submersibles@psubs.org
>Subject: Re: [PSUBS-MAILIST] Pressure air drive.
>Date: Thu, 09 Jan 2003 17:54:39 +0100
>
>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
> >
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