suggestions: frame pump

Sandy said:

"Robert Chung" <[email hidden]> a écrit dans le message de :
news:[email hidden]...

Quoted message said:

Compressed CO2 (at normal temperatures) takes a liquid form so
it's relatively dense at relatively low pressure -- in order to get the
same amount

Amount - what measure ? weight shouldn't matter - expanded volume in a
tube at 8 bars ?

Yup, I meant the same amount of expanded volume at a given pressure (and
temperature).

Quoted message said:

Quoted message said:

of air into the same size container, you have to pump the
pressure higher. That makes pumping CO2 into containers cheaper than
pumping in plain air, and it makes releasing pressure from a CO2
container much safer. That's why it's possible to use a CO2 fire
extinguisher with one hand -- if you tried releasing pressure from a
tank of plain air of similar size with similar contents, it'd blow you
backwards.

I'm too sleepy to be sure I get this. I thought that if the objective
were to achieve a pressure equilibrium of around 8 bars after releasing
the compressed gas, the closed pressure of the cartridge would be the
same. What am I failing to grasp ? Is it the conversion to liquid when
pressurized in the cartridge that makes this work ?

Pretty much, yes. The conversion from liquid to vapor state regulates how
fast a CO2 cartridge can empty: compared to plain air which stays in a gas
state, it empties with a relatively long and steady whooooosh! rather than
a short and sudden WHOOSH!!! (or, in unpleasant circumstances, a loud and
violent BOOM!).

Quoted message said:

Quoted message said:

That's also
the reason why paintball enthusiasts prefer to use compressed air: it
pushes those paintball pellets much farther than compressed CO2.

Does that mean that you *can* get air cartridges ?

You can certainly get HPA cartridges. I don't think you can get a HPA
cartridge that can be appropriately used in a pocket-sized bicycle tire
inflation system.

On Tue, 22 Feb 2005 07:34:09 +0100, "Sandy" <[email hidden]>

Quoted message said:

"Robert Chung" <[email hidden]> a écrit dans le message de :
news:[email hidden]...

Quoted message said:

Sandy said:

Bursting in with a side question (so top posting) : why do they only
come as CO2 and not just plain air ? CO2 seems to leak out at an
astoundingly fast rate, must cost more to segregate than just putting
air into cylinders.

Why oh why CO2 ?

CO2 molecules are larger than N2, so it shouldn't leak out faster than
plain air.

Having looked at Carl's references, I am willing to accept their
conclusions. My own are only from experience, knowing that you have to
replenish the tire relatively quickly, if it's full of CO2.

Quoted message said:

Compressed CO2 (at normal temperatures) takes a liquid form so
it's relatively dense at relatively low pressure -- in order to get the
same amount

Amount - what measure ? weight shouldn't matter - expanded volume in a tube
at 8 bars ?

Quoted message said:

of air into the same size container, you have to pump the
pressure higher. That makes pumping CO2 into containers cheaper than
pumping in plain air, and it makes releasing pressure from a CO2 container
much safer. That's why it's possible to use a CO2 fire extinguisher with
one hand -- if you tried releasing pressure from a tank of plain air of
similar size with similar contents, it'd blow you backwards.

I'm too sleepy to be sure I get this. I thought that if the objective were
to achieve a pressure equilibrium of around 8 bars after releasing the
compressed gas, the closed pressure of the cartridge would be the same.
What am I failing to grasp ? Is it the conversion to liquid when
pressurized in the cartridge that makes this work ?

Quoted message said:

That's also
the reason why paintball enthusiasts prefer to use compressed air: it
pushes those paintball pellets much farther than compressed CO2.

Does that mean that you *can* get air cartridges ?

Dear Sandy,

I'm a bit puzzled by Robert's reply, too.

If you're ejecting pure gas from a compressed source, CO2
has more mass than pure N2, pure O2, or the typical
atmospheric 80/20 mix of 02 and N2--CO2 is heavier and would
have more recoil, not less.

A CO2 fire extinguisher is used because CO2 smothers fire.
Compressed air would increase the fire, not extinguish
it--you'd just be force-feeding the fire with a fresh charge
of 20% O2. CO2 condenses and even freezes at much higher
temperatures than O2. Since the rapid expression of
room-temperature compressed CO2 involves massive cooling,
you can get bits of frozen CO2:

http://www.fire-extinguisher101.com/how-work.html

In air-rifles, CO2 is quick, cheap, and convenient. At
normal temperatures, it liquifies at a comparatively low
pressure. It gives instant power, many shots, and reasonable
accuracy.

For real high-power air guns, scuba tank 3000 psi pressure
is used. It's considerably more expensive and not really
necessary for assassinating small, inoffensive creatures.

For the accuracy fiends, single-stroke lever-compression air
rifles are prized. They give more consistent pressure than
CO2 cartridges, whose output varies enough with the outdoor
temperature to make the shots go high or low.

The other reason that match shooters prefer single-stroke
air-guns is that power is not only unimportant (they're just
punching holes in paper targets at twenty paces) but
actually undesirable. Match-grade .22 ammunition is
deliberately loaded down to a muzzle velocity below the
speed of sound. This avoids the slight loss of accuracy when
a slug breaks the sound barrier. (For those who find such
things hard to believe, it should be pointed out that the
bullseye on a military 50-foot target is a dot not much
bigger than this period.)

Here's a page that explains some of these ballistic points:

http://airgunsbbguns.com/airgun-information-co2-pneumatic--airguns-spring-piston-airguns.html

The air versus CO2 question in paintball is unfamiliar to
me, but I suspect that it's a matter of 3,000 psi
scuba-style guns versus the much lower pressure and cost of
CO2 cartridges. The paintball guns were originally used to
shoot cattle, not for slaughter, but just to mark the beasts
quickly, safely, and conveniently in large pens--there was
no need for the rapid fire and high velocity of game
players.

Carl Fogel

On Tue, 22 Feb 2005 07:34:09 +0100, "Sandy" <[email hidden]>

Quoted message said:

"Robert Chung" <[email hidden]> a écrit dans le message de :
news:[email hidden]...

Quoted message said:

Sandy said:

Bursting in with a side question (so top posting) : why do they only
come as CO2 and not just plain air ? CO2 seems to leak out at an
astoundingly fast rate, must cost more to segregate than just putting
air into cylinders.

Why oh why CO2 ?

CO2 molecules are larger than N2, so it shouldn't leak out faster than
plain air.

Having looked at Carl's references, I am willing to accept their
conclusions. My own are only from experience, knowing that you have to
replenish the tire relatively quickly, if it's full of CO2.

Quoted message said:

Compressed CO2 (at normal temperatures) takes a liquid form so
it's relatively dense at relatively low pressure -- in order to get the
same amount

Amount - what measure ? weight shouldn't matter - expanded volume in a tube
at 8 bars ?

Quoted message said:

of air into the same size container, you have to pump the
pressure higher. That makes pumping CO2 into containers cheaper than
pumping in plain air, and it makes releasing pressure from a CO2 container
much safer. That's why it's possible to use a CO2 fire extinguisher with
one hand -- if you tried releasing pressure from a tank of plain air of
similar size with similar contents, it'd blow you backwards.

I'm too sleepy to be sure I get this. I thought that if the objective were
to achieve a pressure equilibrium of around 8 bars after releasing the
compressed gas, the closed pressure of the cartridge would be the same.
What am I failing to grasp ? Is it the conversion to liquid when
pressurized in the cartridge that makes this work ?

Quoted message said:

That's also
the reason why paintball enthusiasts prefer to use compressed air: it
pushes those paintball pellets much farther than compressed CO2.

Does that mean that you *can* get air cartridges ?

Dear Sandy,

I'm a bit puzzled by Robert's reply, too.

If you're ejecting pure gas from a compressed source, CO2
has more mass than pure N2, pure O2, or the typical
atmospheric 80/20 mix of 02 and N2--CO2 is heavier and would
have more recoil, not less.

A CO2 fire extinguisher is used because CO2 smothers fire.
Compressed air would increase the fire, not extinguish
it--you'd just be force-feeding the fire with a fresh charge
of 20% O2. CO2 condenses and even freezes at much higher
temperatures than O2. Since the rapid expression of
room-temperature compressed CO2 involves massive cooling,
you can get bits of frozen CO2:

http://www.fire-extinguisher101.com/how-work.html

In air-rifles, CO2 is quick, cheap, and convenient. At
normal temperatures, it liquifies at a comparatively low
pressure. It gives instant power, many shots, and reasonable
accuracy.

For real high-power air guns, scuba tank 3000 psi pressure
is used. It's considerably more expensive and not really
necessary for assassinating small, inoffensive creatures.

For the accuracy fiends, single-stroke lever-compression air
rifles are prized. They give more consistent pressure than
CO2 cartridges, whose output varies enough with the outdoor
temperature to make the shots go high or low.

The other reason that match shooters prefer single-stroke
air-guns is that power is not only unimportant (they're just
punching holes in paper targets at twenty paces) but
actually undesirable. Match-grade .22 ammunition is
deliberately loaded down to a muzzle velocity below the
speed of sound. This avoids the slight loss of accuracy when
a slug breaks the sound barrier. (For those who find such
things hard to believe, it should be pointed out that the
bullseye on a military 50-foot target is a dot not much
bigger than this period.)

Here's a page that explains some of these ballistic points:

http://airgunsbbguns.com/airgun-information-co2-pneumatic--airguns-spring-piston-airguns.html

The air versus CO2 question in paintball is unfamiliar to
me, but I suspect that it's a matter of 3,000 psi
scuba-style guns versus the much lower pressure and cost of
CO2 cartridges. The paintball guns were originally used to
shoot cattle, not for slaughter, but just to mark the beasts
quickly, safely, and conveniently in large pens--there was
no need for the rapid fire and high velocity of game
players.

Carl Fogel

Quoted message said:

I'm a bit puzzled by Robert's reply, too.

If you're ejecting pure gas from a compressed source, CO2
has more mass than pure N2, pure O2, or the typical
atmospheric 80/20 mix of 02 and N2--CO2 is heavier and would
have more recoil, not less.

The point is that the CO2 in a cartridge isn't a pure gas--it's a mixture
of liquid and gas. It's that state change that makes CO2 convenient. The
ideal gas law relating pressure, volume, and temperature is, as the name
implies, a law about gases, not liquids.

Quoted message said:

A CO2 fire extinguisher is used because CO2 smothers fire.
Compressed air would increase the fire, not extinguish
it--you'd just be force-feeding the fire with a fresh charge
of 20% O2.

Yeah. If you go back and look, I didn't say that fire extinguishers could
use compressed air -- I was making a comparison about tanks of similar
size, not the way the contents of those tanks are used. Discharging a
fire-extinguisher-sized tank of compressed air of equivalent uncompressed
volume would, if unregulated, blow you backwards. The same would apply to
a tank of compressed nitrogen.

Quoted message said:

CO2 condenses and even freezes at much higher
temperatures than O2.

Bingo.

Quoted message said:

At
normal temperatures, it liquifies at a comparatively low
pressure.

Bingo, twice.

Quoted message said:

The air versus CO2 question in paintball is unfamiliar to
me, but I suspect that it's a matter of 3,000 psi
scuba-style guns versus the much lower pressure and cost of
CO2 cartridges.

Bingo, three times.

Robert Chung said:

CO2 molecules are larger than N2, so it shouldn't leak out faster than
plain air.

The CO2 solvent properties permit it to migrate more quickly through
the butyl tire.

On Mon, 21 Feb 2005 14:56:50 -0800, JOHN CORDELL

may have said:

Sandy said:

Bursting in with a side question (so top posting) : why do they only
come as CO2 and not just plain air ? CO2 seems to leak out at an
astoundingly fast rate, must cost more to segregate than just putting
air into cylinders.

Why oh why CO2 ?

Maybe because it has no water vapor to it? Under compression, the
moisture might become a factor? Just a guess. thanks to everyone for the
suggestions. JC

The condensation temperature of CO2 is far higher than that of air.
This fact skews its temp/pressure curve to permit more grams of
compressed CO2 to be put into the cartridge than could be accomplished
at the same pressure with air, but the curve is still not at such a
steep angle that you get huge in-tire pressure differences with common
environmental temp variances. The drawback, as you've noted, is that
CO2 is more soluble than the rest of the major fractions of air in
most tire and tube compounds, leading to a higher rate of pressure
loss. At one time, R12 refrigerant was sold as an emergency tire
inflation gas, but it goes through some tire compounds even faster
than CO2. Propane and butane have long been used as inflation gasses
by farmers, and some of them use propane as a refrigerant as well. It
works, but these practices are best regarded as Something You Should
Not Try Yourself.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

Paul Kopit said:

Robert Chung said:

CO2 molecules are larger than N2, so it shouldn't leak out faster than
plain air.

The CO2 solvent properties permit it to migrate more quickly through
the butyl tire.

Thanks for the correction.

S o r n i said:

JOHN CORDELL said:

I finally broke my frame pump and am looking for a new one. What is
the best frame pump out there? I am using presta valves and running
over 100 psi on my road tires. I don't want CO2. Suggestions
appreciatd. thanks, JC

I'll doubtless get flamed for this, but the long skinny Performance
"Hurricane" frame pump works surprisingly well and easily. Get one
on sale (like, $12.99? $9.99??), and it's downright cheap. (Like
me.)

BAHAHAHHAHA you're retarded!!!
--
Phil, Squid-in-Training (how was that?)

Phil said:

S o r n i said:

JOHN CORDELL said:

I finally broke my frame pump and am looking for a new one. What is
the best frame pump out there? I am using presta valves and running
over 100 psi on my road tires. I don't want CO2. Suggestions
appreciatd. thanks, JC

I'll doubtless get flamed for this, but the long skinny Performance
"Hurricane" frame pump works surprisingly well and easily. Get one
on sale (like, $12.99? $9.99??), and it's downright cheap. (Like
me.)

BAHAHAHHAHA you're retarded!!!

TYVM.

Bill "vindicated" S.