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Re: [PSUBS-MAILIST] Pressure air drive.

To: <personal_submersibles@psubs.org>
Subject: Re: [PSUBS-MAILIST] Pressure air drive.
From: "Herve" <caribsub@coqui.net>
Date: Thu, 9 Jan 2003 23:05:45 -0500
References: <OFACBA071E.2F2B4E6A-ON87256CAA.000F597B@bjservices.ca>
No matter how you calculate air pressure, air flow or whatever, you will
never produce more energy at the prop than you used to store it.
Remember that it is  only energy transfer, from charger to battery to prop,
or from compressor to tank to prop, you get less at the prop than you put in
because even the most efficient machinery is 90% efficient max.
So whether it is battery or air, if you used lets say 1000Watt/hour to
refill your air tank, or 1000Watt/hour to recharge your battery, you will
get at the most 80 or 90% of that at the prop. But in the case of the air
storage you lose capacity the deeper you go, you actually waste your energy
because at depth the air that you use has not expanded completely  until it
hits the surface. In other words You need twice the amount of air for the
same power at 33 Ft than you would use at the surface.
Any search or calculations for new systems like air motors should also
include 2 basic questions to avoid waste of time and taking the wrong
direction and reinventing things, like:
is it used today by commercial companies or military, yes / no,
if it was used before, why it is not used anymore
Herve

----- Original Message -----
From: <jbarlow@bjservices.ca>
To: <personal_submersibles@psubs.org>
Sent: Thursday, January 09, 2003 10:21 PM
Subject: Re: [PSUBS-MAILIST] Pressure air drive.


>
> Sorry Pierre,
>       I realise that this wasn't addressed to me but I felt compelled to
> have one last flogging at the long dead and decomposed horse.
> I had a hard time finding this because most air tools are rated on the
> supply air.  Here is one on exhaust.  However I think a simple low
pressure
> test would be free easy prior to spending money.
>
> http://www.irtools.com/industrial/ecatalog.html
>
>  Model TD 250RG4K is the basis of these comparison calcs.  I can't seem to
> link to that page directly, but if you use the search by model No. it
seems
> to work.
>
>
> Note that this model generates 0.7 hp at 25000 rpm using 90 psi supply
air.
> Roughly the same as the one previously discussed. Air consumption is
stated
> as 26 cfm.
>
> P1 V1 = P2 V2
> Solving for V2
>  90 psi x 3 cfm = 14.7 psi (x)
> (x) = 18.36 cfm
>
> Using Jay's Method to generate 0.6hp
> Remember that this number is small because air is not an ideal gas.  That
> would likely account for the difference between the 22.28 cfm and 26 cfm
> below.
> ____________________________________
>
>
> Unless you believe that the one you found is so much more  efficient (3cfm
> : 26 cfm = 866%).  Actually taking into account the hp differences the
> number is a little less if you count in the hp differences.
>   0.6 hp / 0.7 hp = 85%
> 0.85 x 26 cfm (to put them on an even playing field) = 22.28 cfm
>
> Then the difference becomes 3 cfm : 22.28 = 742%
>
>
> You can buy simple in-line oilers for these air tools.  Moisture can be
> taken care of by a trap in the line you use to fill your tanks prior to
> your excursion, the length of which seems to be the subject of some
debate.
> The tools are that fussy about a little bit in the supply air.  They are
> used in shops all the time without air dryers.  The exhaust valve would be
> elegant to be a check valve but it might be cheaper for a ball valve to
> shut of the exhaust. It would stall the motor and stop water from entering
> the motor.
>
> I promise to shut up about this and behave now.
>
>
> 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
>
>
>                       09/01/2003 07:25 PM
>                       Please respond to
>                       personal_submersibles
>
>
>
>
>
>
> 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
> > >
> > > _________________________________________________________________
> > > MSN Search, le moteur de recherche qui pense comme vous !
> > > http://search.msn.fr/worldwide.asp
>
>
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References:
- Re: [PSUBS-MAILIST] Pressure air drive.
  - From: jbarlow@bjservices.ca
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