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Re: [PSUBS-MAILIST] Pressure air drive.
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