[Date Prev][Date Next]
[Chronological]
[Thread]
[Top]
Re: [PSUBS-MAILIST] Pressure air drive.
Herve: Excellent stuff. Thanks. One of the most dangerous aspects of SCUBA cylinders that I am familiar with is high heat. Anytime aluminum cylinders are exposed to high heat, they turn extremely brittle. Several years ago when I was diving a lot more, it became the rage to have the wildest paint scheme on SCUBA tanks. One method was to coat the tank with a particular paint that required it to be baked for a time. A set of twin aluminum cylinders were treated this way and upon their refill at the dive shop compressor, they exploded. I did not know the dive shop operator but heard about it later. When the tanks blew, they removed both his legs and destroyed the shop. For a long time, no one would even think about filling re-painted aluminum cylinders unless they knew their history. Steel cylinders, I'm sure, are much safer.This has been several years ago and I assume nothing has changed. Thought I would pass this along. It is something I have remembered for a long time. Beest regards, Mark Steed
---------- Original Message ----------------------------------
From: "Herve" <caribsub@coqui.net>
Reply-To: personal_submersibles@psubs.org
Date: Thu, 9 Jan 2003 13:42:29 -0400
>Yes all scuba tanks have different sizes in the US, a100cuft aluminium tank
>(3000 psi) is bigger than a steel 100 cuft tank (3500 psi), expended air is
>the same, but volume of compressed air is different depending of the
>pressure.
>
>It is prohibited to refill breathing air tanks from industrial compressor,
>or air shop compressors. Scuba HP compressors are designed to fill up
>cylinders with high pressure with no moisture or contaminated gas.
>When you compress air, temp goes up and oil or grease residuts, if any, but
>present in industrial comp can burn and produce CO, which is odorless.
>Moisture in tanks creates oxydations inside, even in a aluminium tank and
>weakens the walls.
>In 1981 during my first scuba dive in the NAVY, 2 experienced divers on
>another task died because of that. It was a n old compressor, and somebody
>reversed a set of filters, which produced CO due to the high temperature.
>They both lost conscience and drawned and never forgot that. So a good
>advise.... use dedicated compressors to refill tanks and other life support
>air sytems, and leave shop air compressors for air tools.
>Herve
>----- 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
>> >
>> > _________________________________________________________________
>> > MSN Search, le moteur de recherche qui pense comme vous !
>> > http://search.msn.fr/worldwide.asp
>>
>>
>>
>
>