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"Leon" wrote in message
You quoted him so I saw what Doug Miller had to say and,,,,,


Say no more ... some would argue that's justification for another 'plonk'
right there!

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On Apr 28, 2:06 pm, "Leon" wrote:
Doug Miller wrote:
In article , "Leon"
wrote:


You are on the right track.
Actually the compressed air does not create the condensation. It is
the heat generated from compressing the humid air that causes the
condensation.


Incorrect. It is *exactly* the compression that causes the condensation:
water that is vapor at ambient pressure can be condensed into liquid by
increasing the pressure.


So Doug, I suspect you believe it is the pressure from "your firm grip" on
a glass of ice water that causes the warm humid air surrounding the glass to
cause condensation on the cool side of the glass.


In his case, it would likely be a glass of vinegar.
It would be better if it was bourbon or something, maybe he'd lighten-
the-****-up.

but alas... I said too much.

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In article , "Leon" wrote:


Doug Miller wrote:
In article , "Leon"
wrote:


You are on the right track.
Actually the compressed air does not create the condensation. It is
the heat generated from compressing the humid air that causes the
condensation.

Incorrect. It is *exactly* the compression that causes the condensation:
water that is vapor at ambient pressure can be condensed into liquid by
increasing the pressure.


So Doug, I suspect you believe it is the pressure from "your firm grip" on
a glass of ice water that causes the warm humid air surrounding the glass to
cause condensation on the cool side of the glass.


Of course not. Vapor condenses as a result of being compressed, or cooled, or
both -- but never as a result of being heated. Warm humid air surrounding a
glass of ice water produces condensation on the side of the glass because the
temperature of the surface of the glass is below the dew point. The water
vapor condenses because it is cooled.

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It's time to throw all their damned tea in the harbor again.
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In article , "Leon" wrote:
You quoted him so I saw what Doug Miller had to say and,,,,,

I must say, isn't it polite jesture how Doug always ends his often toxic and
condecending comments with,

Regards,
Doug Miller


LOL


I guess you're not familiar with the concept of a "sig" ?



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It's time to throw all their damned tea in the harbor again.
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In article , "Leon" wrote:
You quoted him so I saw what Doug Miller had to say and,,,,,

I must say, isn't it polite jesture how Doug always ends his often toxic and
condecending comments with,

Regards,
Doug Miller


LOL


You just can't *stand* it when I point out a mistake you made, can you?

Grow up, why dontcha?


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Dew point, condensation, partial pressures, humidity; come on guys. To
roughly quote a former ng participant, "lets stick to stuff we know
something about, like lektricity."


--
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Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
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On Apr 26, 6:50 pm, "Buck Turgidson" wrote:
Partially out of laziness, inertia, procrastination, and partially because I
use it several times a month, I leave my Porter Cable air compressor full.
Does this do longterm harm to the machine?


On a related question... why are air dryers placed after the
compressor and not before it?

Thanks

TMT

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In article om,
Too_Many_Tools wrote:

On Apr 26, 6:50 pm, "Buck Turgidson" wrote:
Partially out of laziness, inertia, procrastination, and partially because I
use it several times a month, I leave my Porter Cable air compressor full.
Does this do longterm harm to the machine?


On a related question... why are air dryers placed after the
compressor and not before it?


To protect the tools instead of the tank.

--
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Too_Many_Tools wrote:

On a related question... why are air dryers placed after the
compressor and not before it?


Remember, "Willie, The Actor" Sullivan, a bank robber of some notarity.

When asked, "Willie, why do you rob banks?"

He answered, "Because that's where they keep the money."

Why put a dryer after the compressor, because that is where the water is.

Lew
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On Sun, 29 Apr 2007 05:11:22 GMT, Lew Hodgett
wrote:

Too_Many_Tools wrote:

On a related question... why are air dryers placed after the
compressor and not before it?


Remember, "Willie, The Actor" Sullivan, a bank robber of some notarity.

When asked, "Willie, why do you rob banks?"

He answered, "Because that's where they keep the money."

Why put a dryer after the compressor, because that is where the water is.

Lew



If you dry the air going into the compressor, you'll have dry air in
the storage tank. The compressor doesn't create water.


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In article , Tom Veatch wrote:
On Sun, 29 Apr 2007 05:11:22 GMT, Lew Hodgett
wrote:

Too_Many_Tools wrote:

...snipped...
Why put a dryer after the compressor, because that is where the water is.

Lew



If you dry the air going into the compressor, you'll have dry air in
the storage tank. The compressor doesn't create water.


If the humidity could be removed before the air was compressed, that would
be true. However, the air dryer, working on compressed air at say
150psi, has 10 times as much air in contact with its cooling fins
as it would with air at atmospheric pressure. These units work more
or less as dehumidfiers. To operate on the input side of a compressor
would just be much less efficient.


--
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Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
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"Lew Hodgett" wrote in message
nk.net...
Too_Many_Tools wrote:

On a related question... why are air dryers placed after the
compressor and not before it?


Remember, "Willie, The Actor" Sullivan, a bank robber of some notarity.


No, not all. Mr. Sullivan never robbed banks. Willie Sutton did.

Real fact is, he did not make that statement but is from the mind of some
reporter. He did, however, enjoy robbing banks and said so.





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"Larry W" wrote in message
...
Dew point, condensation, partial pressures, humidity; come on guys. To
roughly quote a former ng participant, "lets stick to stuff we know
something about, like lektricity."



Well, good point, but through the years we have learned a lot about water in
the tank also. ;~)






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Tom Veatch wrote in message
...
On Sun, 29 Apr 2007 05:11:22 GMT, Lew Hodgett
wrote:



If you dry the air going into the compressor, you'll have dry air in
the storage tank. The compressor doesn't create water.


Consider this. Given the proper sized compressor the amount of air being
dried on the "exhaust side" is much less than the air on the "in take" side.
The dryer would have to dry much faster on the intake side. Typically with
the correct sized compressor for the task at hand the exhaust side releases
air at a smaller CFM than the intake side. Additionally, the compressor
tank catches a majority of the water and lessens the work on the dryer.


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On Sun, 29 Apr 2007 11:20:49 -0500, "Leon"
wrote:


Tom Veatch wrote in message
.. .
On Sun, 29 Apr 2007 05:11:22 GMT, Lew Hodgett
wrote:



If you dry the air going into the compressor, you'll have dry air in
the storage tank. The compressor doesn't create water.


Consider this. Given the proper sized compressor the amount of air being
dried on the "exhaust side" is much less than the air on the "in take" side.
The dryer would have to dry much faster on the intake side. Typically with
the correct sized compressor for the task at hand the exhaust side releases
air at a smaller CFM than the intake side. Additionally, the compressor
tank catches a majority of the water and lessens the work on the dryer.


Not to mention, as I previously stated, the state change physics of
water is such that higher pressure at a given temperature in a closed
container forces the equilibrium point toward more condensation.

Assuming the temperature of the air entering the dryer is the same in
either case, the pressure upstream of the compressor is less than it
is downstream of the tank. Therefore, a given drying process located
downstream of the tank operates at higher pressure and condenses more
water from a given mass of air than it would if that same process were
operating upstream of the compressor. Repeat, that's assuming the
process occurs at the same temperature in both cases.

My comment "... The compressor doesn't create water." was directed at
a previous post that stated "That's where the water is." It is
patently obvious that a given mass of air contains the same amount of
water entering the compressor as it does exiting the compressor and
entering the storage tank. The compressor might add oil vapor to the
air but it doesn't add water.

Technical discussion follows, skip it if you wish.

Atmospheric air is a mixture of gasses which includes some amount of
water vapor. The partial pressure of each gas in the mixture is
related to the total pressure in the same ratio as the number of
molecules of each gas is related to the total number of molecules in
the sample. For example, and using round numbers for convenience, if
the air contains 1% water vapor and is compressed to 100psi, the
partial pressure of the water is 1psi. At 200psi, the partial pressure
of the water is 2psi.

As the sample of gas is compressed, the partial pressure of the water
vapor increases in proportion to the increase in total pressure. At
any given temperature, water has a specific vapor pressure which
increases as the temperature increases. If the partial pressure of the
vapor is greater than the vapor pressure of the liquid at that
temperature, the rate of condensation will exceed the rate of
evaporation and the amount of vapor will decrease as the amount of
liquid increases. Net condensation will occur until the partial
pressure of the remaining vapor becomes equal to the vapor pressure of
the liquid. That is the equilibrium point where the rates of
condensation and evaporation are equal to each other.

From that point, isothermal compression causes net condensation and an
increase in the amount of liquid in the container. The reverse is true
for Isothermal expansion. Isobaric temperature increase drives net
evaporation. The amount of liquid reduces and the amount of vapor
increases until the partial pressure of the vapor again equals the
vapor pressure of the liquid. Likewise, isobaric temperature decrease
drives net condensation.

Everything that is correct in this thread follows from those basic
facts of physics.


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Tom Veatch wrote in message
Everything that is correct in this thread follows from those basic
facts of physics.


That easy. Now try to explain where everything wrong in this thread came
from. C'mon, I dare ya!


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If the compressor is full of water, will the water put out the fire
after the ungrounded dust collector explosion?
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On Sun, 29 Apr 2007 17:16:20 -0400, "Edwin Pawlowski"
wrote:

That easy. Now try to explain where everything wrong in this thread came
from. C'mon, I dare ya!


Oops, no time for that now, I just remembered that my wife wants some
bookshelves built.

I will say in response to the OP, if I can remember what the OP asked,
that there is no structural reason to completely depressurize the tank
after each use, and there is a theoretical reason to leave the tank
pressurized. Deep cyclic loading, i.e., full pressurization followed
by complete depressurization, induces fatigue damage to the vessel. In
a well designed and constructed tank, that damage is insignificant at
the pressures shop compressors usually develop and can be ignored. On
the other hand, it does no harm to the tank to leave it pressurized.
Static loading doesn't cause metal fatigue. If you want to avoid
cycling due to minor leakage and long periods of disuse, simply turn
off the compressor when you're done.

Draining condensation is another matter. That should be done
regularly, either manually or with an auto drain valve, whether or not
the tank is left pressurized.

Now, I hear those bookshelves calling!
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Tom Veatch wrote:

Oops, no time for that now, I just remembered that my wife wants some
bookshelves built.


First thing debaters and lawyers learn to do is use the facts, if you
have them.

If you don't, keep throwing crap on the wall and hope some of it sticks.

Given air at 0 PSIG, 70F, and 50% relative humidity and two (2), 10
cubic foot containers.

Container #1 is filled with 0 PSIG air and sealed.

Container #2 is filled with the same air, except compressed to 100 PSIG.

Question:

Which container contains the most pounds of water vapor?

End of discussion.

Lew
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"B A R R Y" wrote in message
If the compressor is full of water, will the water put out the fire
after the ungrounded dust collector explosion?


Yabbut, that depends upon whether the HP rating of the compressor is correct
for its voltage, whether the circuit ampacity is properly sized for start up
voltage, with NEC approved and properly sized conductors attached to a
circuit breaker, of sufficient ampacity, in a properly grounded, or properly
ungrounded, sub panel.

But hey, look on the bright side ... the BIG question has been answered!
Whether or not that damp spot on the shop floor is actually from rising sea
levels due to human induced global warming, the shop dog not being let out,
or water leaking from the compressor tank?

Gee ... just think, now that we know how/why it got there on a molecular
level, we don't have to worry about that no more!

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On Apr 29, 7:24 pm, Lew Hodgett wrote:


Question:

Which container contains the most pounds of water vapor?


That would be the shop-dog's bladder.

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On Sun, 29 Apr 2007 23:24:57 GMT, Lew Hodgett
wrote:


Which container contains the most pounds of water vapor?


An interesting question. The obvious answer is that the second one
would contain 7.67 times as much water vapor. (Assuming 15psi
atmospheric pressure, 115/15 = 7.67). But that ignores state change.

Since I don't have the appropriate property tables memorized, do not
have copies near to hand, and am not inclined to try and find any for
this academic exercise, I will make some assumptions.

The question states that the final temperature is 70F in both cases.
Therefore, the H2O vapor pressure is the same in both cases. But, we
know the partial pressure of the H2O vapor in the first container is
less than the 70F vapor pressure since the air is not saturated, being
at only 50% RH.

Assuming that, since the air in the first container is at 70F and 50%
RH, the partial pressure of the vapor in the first container is 50% of
the H2O 70F vapor pressure. In that case, a 7.67 compression ratio
will increase the partial pressure of the vapor in the second
container to well above the H2O 70F vapor pressure and condensation
will occur as the compressed air cools to the 70F ambient temperature.
Most of the water will condense out leaving the air in the second
container saturated at 100% RH with a H2O partial pressure equal to
the 70F vapor pressure. This is double the assumed partial pressure in
the first container. So, if the assumption above is correct, the
second container will contain twice the mass of water vapor as the
first container with the remainder of the water condensed as liquid.

And, your point about lawyers, debaters, and crap stuck to the walls
is...?
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Tom Veatch wrote:


An interesting question. The obvious answer is that the second one
would contain 7.67 times as much water vapor. (Assuming 15psi
atmospheric pressure, 115/15 = 7.67).


Give that man a cigar.

But that ignores state change.


Not relevant, pounds is pounds.

Lew



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On Mon, 30 Apr 2007 01:58:02 GMT, Lew Hodgett
wrote:

Not relevant, pounds is pounds


But the question was which one would contain the most water "vapor".
So state change has to be considered.
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Tom Veatch wrote:

But the question was which one would contain the most water "vapor".
So state change has to be considered.


Use the general energy equation to develop the specific equation for
the conditions at hand.

It all drops out to yield pounds is pounds. Vapor, liquid, gas, who
cares, it is still weight (Mass if you prefer).

The whole thread got started in answer to a question about where to
locate a dryer in a compressed air system.

My smart ass response was "Where the water is" or something close,
thus on the high pressure, not the low pressure side of the compressor.

I stand by that statement.

Lew


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"Lew Hodgett" wrote in message
ink.net...
Tom Veatch wrote:

But the question was which one would contain the most water "vapor".
So state change has to be considered.


Use the general energy equation to develop the specific equation for the
conditions at hand.

It all drops out to yield pounds is pounds. Vapor, liquid, gas, who cares,
it is still weight (Mass if you prefer).

The whole thread got started in answer to a question about where to locate
a dryer in a compressed air system.

My smart ass response was "Where the water is" or something close, thus on
the high pressure, not the low pressure side of the compressor.

I stand by that statement.

Lew


Lew:
Previously: "Question: Which container contains the most pounds of water
vapor? End of discussion."
Now: "Vapor, liquid, gas, who cares, it is still weight"

I wonder what debaters and lawyers do when called on an error. They
probably don't just admit it. They redefine the question.

todd




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On 27 Apr, 16:10, B A R R Y wrote:
Andy Dingley wrote:

In general, no. However a machine that has a slow leak down somewhere
and is going to be switched off for long enough to empty itself is
usually best vented deliberately rather than being left to do it
inevitably itself (or just fix the leak!)


Why is that?


A compressor is a pressure vessel, i.e. it's potentially dangerous if
left pressurised. The risk is small, the convenience and energy saving
of leaving it full outweighs this if we're going to come back to it
later and use that stored pressure.

However if we've got a leak, or we're leaving it for a long time such
that we're _not_ going to benefit from that stored energy, then good
practice is to not leave it lying around. You don't know what it's
going to do, but it ain't going to bake you a cake. There's also the
risk of leaving the compressor powered up (and leaking), which is just
a sizable waste of energy.


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Andy Dingley wrote:

However if we've got a leak, or we're leaving it for a long time such
that we're _not_ going to benefit from that stored energy, then good
practice is to not leave it lying around.


Sounds pretty anal to me.


There's also the
risk of leaving the compressor powered up (and leaking), which is just
a sizable waste of energy.


Agreed on that one.

What if it takes my compressor a week or two to drain down, so there's a
sizable change I might use the energy? If I have half left, I use half
as much enegery refilling the tank.
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On Mon, 30 Apr 2007 17:41:08 GMT, B A R R Y
wrote:


What if it takes my compressor a week or two to drain down, so there's a
sizable change I might use the energy? If I have half left, I use half
as much enegery refilling the tank.



Leave the tank pressurized and shut power off to the motor.

The normal failure mode of a tank pressurized within specifications is
to develop a pinhole leak, not to explode catastrophically. So there
is very little risk in leaving it pressurized. Understand that is not
the case if the failure is due to overpressurization. In that case,
the failure can be catastrophic so make sure the pressure relief valve
is properly set and functioning.
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"B A R R Y" wrote in message

What if it takes my compressor a week or two to drain down, so there's a
sizable change I might use the energy? If I have half left, I use half as
much enegery refilling the tank.


But does it take more energy to fill the second half than the first half?




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On Apr 30, 11:01 pm, "Edwin Pawlowski" wrote:
"B A R R Y" wrote in message



What if it takes my compressor a week or two to drain down, so there's a
sizable change I might use the energy? If I have half left, I use half as
much enegery refilling the tank.


But does it take more energy to fill the second half than the first half?


Yes

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Tom Veatch wrote:
On Mon, 30 Apr 2007 17:41:08 GMT, B A R R Y
wrote:

What if it takes my compressor a week or two to drain down, so there's a
sizable change I might use the energy? If I have half left, I use half
as much enegery refilling the tank.



Leave the tank pressurized and shut power off to the motor.


I do.
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Edwin Pawlowski wrote:
"B A R R Y" wrote in message
What if it takes my compressor a week or two to drain down, so there's a
sizable change I might use the energy? If I have half left, I use half as
much enegery refilling the tank.


But does it take more energy to fill the second half than the first half?


I'll never know, because I leave it full and switch it on when I need
it. Sometimes the motor starts, other times it doesn't.

I sleep well, too! G
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Edwin Pawlowski wrote:
Tom Veatch wrote in message
Everything that is correct in this thread follows from those basic
facts of physics.


That easy. Now try to explain where everything wrong in this thread came
from. C'mon, I dare ya!


Egypt?

It's just a guess. ;-)


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