Re: [PSUBS-MAILIST] Pressure air drive.

[Coalbunny <coalbunny@vcn.com>]

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

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