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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
> >
> > _________________________________________________________________
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