Re: [PSUBS-MAILIST] Pressure air drive.

["Herve" <caribsub@coqui.net>]

90 psi means a differential pressure, 3cfm is the flow required at 15 psi.
In case of a system that uses 2 tanks, you will lose power gradually and
rapidely as the differential pressure will decrease.
This is why air motors are used only in shallow water vehicles.
with a 100 cuft tank you only have 50 cuft left at 33 ft before starting the
motor.
In my opinion air motors are too fragile to work in the harsh sea water
environment. They need to be oiled permanently otherwise they have a short
life.
It is prohibited to re-paint air cylinders. HP cylinders must be inspected
visually every year for corrosion and cracks and presence of residuts
inside, and every 5 years hydrotesting to measure fatigue in the metal.
Those inspections are to be conducted by licensed personnel. It is enforced
by professional who refills tanks and the USCG at sea in case of a control.
In case of an accident that is the first thing to be verified by the
insurance companies.
----- Original Message -----
From: "Carsten Standfuss" <MerlinSub@t-online.de>
To: <personal_submersibles@psubs.org>
Sent: Thursday, January 09, 2003 12:54 PM
Subject: Re: [PSUBS-MAILIST] Pressure air drive.


> 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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