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  #41   Report Post  
Richard J Kinch
 
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PrecisionMachinisT writes:

Ignore the entire concept of latent heat if its convenient to you
then....


Haven't ignored anything.

(Regardless, I suspect you mean sensible heat.)

Point being is the heat was already added or subtrcated from the
sytstem before or after the phase change took place.


The heat initially present in the water itself, or something intimately
in contact with it, will vaporize very little water, and in practice the
ambient heat will not flow in quickly (the vacuum being an insulator).

And this only applies to free water. Ordinary vacuum dessication does
not work for water bound in something like a silica gel dessicant, or
entrained in the oil, or hydrating contaminants.

A lot of people have been taught the pseudo-scientific myth that "water
boils in a vacuum" in some magic sense that it doesn't in the
atmosphere. The truth is that water vaporizes in a vacuum or in the
atmosphere the same way: *only* because you add heat. In the same
sense, water doesn't boil at 212 deg F, it boils because you add more
heat after it is at 212 deg F.

Another related myth is that if *you* were put into a vacuum, your body
would explode or your "blood would boil". Pure bunk.

Another popular (and yes, even in the HVAC trade) myth is "saturation"
of air with humidity, that the moisture is carried or dissolved in the
air, and that it "saturates" like a solution of salt in water.
  #42   Report Post  
PrecisionMachinisT
 
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"Richard J Kinch" wrote in message
. ..
PrecisionMachinisT writes:

Ignore the entire concept of latent heat if its convenient to you
then....


Haven't ignored anything.

(Regardless, I suspect you mean sensible heat.)

Point being is the heat was already added or subtrcated from the
sytstem before or after the phase change took place.


The heat initially present in the water itself, or something intimately
in contact with it, will vaporize very little water, and in practice the
ambient heat will not flow in quickly (the vacuum being an insulator).

And this only applies to free water. Ordinary vacuum dessication does
not work for water bound in something like a silica gel dessicant, or
entrained in the oil, or hydrating contaminants.

A lot of people have been taught the pseudo-scientific myth that "water
boils in a vacuum" in some magic sense that it doesn't in the
atmosphere. The truth is that water vaporizes in a vacuum or in the
atmosphere the same way: *only* because you add heat. In the same
sense, water doesn't boil at 212 deg F, it boils because you add more
heat after it is at 212 deg F.

Another related myth is that if *you* were put into a vacuum, your body
would explode or your "blood would boil". Pure bunk.

Another popular (and yes, even in the HVAC trade) myth is "saturation"
of air with humidity, that the moisture is carried or dissolved in the
air, and that it "saturates" like a solution of salt in water.


Obviously then , some part of "Im done, your a ****wit and my opinion still
stands" has apparently still escaped your attention.

Bye bye idiot troll.........

--

SVL






  #44   Report Post  
TURTLE
 
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"PrecisionMachinisT" wrote in message
...

"Jake" wrote in message
news:CDwNe.48754$084.28178@attbi_s22...
PrecisionMachinisT wrote:
"DiDo" wrote in message
news:BMrNe.128$IG2.84@trndny01...


It is possible! how? well while water boils at low pressures
but it ALSO FREEZES and once it get frozen it does not
boils any more.


Frozen water changes directly from the solid into the vapor phase under

low
pressure conditions, due to a phenomena known as 'sublimation'.....IOW,

no
"boiling" is needed.

http://www.newton.dep.anl.gov/askasc.../chem03598.htm

--

SVL


Sam,

I think Dido is talking about when you have a evap coil exposed to other
cold temps within a running freezer.. a common occurence in the
commercial world.

This is what the man meant, I believe.


Jake,

Doesn't matter--next time it snows, watch your outside temp real close, and
take note of any period over several days, or perhaps up to a week where the
temp stays constantly below freezing....notice that the snow 'just kinda
dissapears'....given enough time, it will eventually dissapear altogether,
without ever reaching a temp above freezing, and without rain falling on it,
etc.....now note that this process speeds up considerably at pressures below
atmospheric.

--

SVL


This is Turtle.

i see the example all the time with ice cub trays all the time. Fill a ice cube
tray with water and let them freeze real good and then keep them in the freezer
for 1 years. You will come back and find all the ice gone out of the ice cube
tray. I call it freezer evaperation or called freezer burning the ice. This
dehydration takes all the moisture out of food product and is called freezer
burn.

TURTLE


  #45   Report Post  
PrecisionMachinisT
 
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wrote in message
...
On Sun, 21 Aug 2005 00:41:04 -0500, Richard J Kinch
wrote:

I am not sure where you live but it is about 600 degrees F warmer than
"space " on earth, even in the winter. There is plenty of available
heat to sublimate water.


Repeat after me: temperature is not heat.


Repeat after me, a gas at a given temperature (ambient air) is heat.


See cat...notice cat has a tail....pull on cat's tail........

Repeat until bored.

--

SVL




  #46   Report Post  
pjm@see_my_sig_for_address.com
 
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On Sun, 21 Aug 2005 10:46:35 -0700, "PrecisionMachinisT"
wrote:


wrote in message
.. .
On Sun, 21 Aug 2005 00:41:04 -0500, Richard J Kinch
wrote:

I am not sure where you live but it is about 600 degrees F warmer than
"space " on earth, even in the winter. There is plenty of available
heat to sublimate water.

Repeat after me: temperature is not heat.


Repeat after me, a gas at a given temperature (ambient air) is heat.


See cat...notice cat has a tail....pull on cat's tail........

Repeat until bored.


See cow.

See cow udders.

Pull cow udders.

Get milk.

If cow only have one udder, get cream.


Click here every day to feed an animal that needs you today !!!

http://www.theanimalrescuesite.com/

Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
  #47   Report Post  
PrecisionMachinisT
 
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wrote in message
news

If cow only have one udder, get cream.


Bull.

--

SVL


  #48   Report Post  
~^Johnny^~
 
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Default

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Sun, 21 Aug 2005 02:15:25 -0500, Richard J Kinch
wrote:

The truth is that water vaporizes in a vacuum or in the
atmosphere the same way: *only* because you add heat. In the same
sense, water doesn't boil at 212 deg F, it boils because you add
more heat after it is at 212 deg F.


Then you're all wet.


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Version: PGP 7.1

iQA/AwUBQwjejAIk7T39FC4ZEQIO9QCguHSRV5tUO06ZeIVnzzonnE DuqsEAnjJ1
Imv1in/cDv3fIdImpY7Mj8dN
=ZMXn
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--
-john
wide-open at throttle dot info
  #49   Report Post  
Joseph
 
Posts: n/a
Default


wrote in message
news
On Sun, 21 Aug 2005 10:46:35 -0700, "PrecisionMachinisT"
wrote:


wrote in message
.. .
On Sun, 21 Aug 2005 00:41:04 -0500, Richard J Kinch
wrote:

I am not sure where you live but it is about 600 degrees F warmer than
"space " on earth, even in the winter. There is plenty of available
heat to sublimate water.

Repeat after me: temperature is not heat.

Repeat after me, a gas at a given temperature (ambient air) is heat.


See cat...notice cat has a tail....pull on cat's tail........

Repeat until bored.


See cow.

See cow udders.

Pull cow udders.

Get milk.

If cow only have one udder, get cream.


"I think I'll go wash up..."



Click here every day to feed an animal that needs you today !!!

http://www.theanimalrescuesite.com/

Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/



  #50   Report Post  
Joseph
 
Posts: n/a
Default


"TURTLE" wrote in message
.. .

"PrecisionMachinisT" wrote in message
...

"Jake" wrote in message
news:CDwNe.48754$084.28178@attbi_s22...
PrecisionMachinisT wrote:
"DiDo" wrote in message
news:BMrNe.128$IG2.84@trndny01...


It is possible! how? well while water boils at low pressures
but it ALSO FREEZES and once it get frozen it does not
boils any more.


Frozen water changes directly from the solid into the vapor phase under

low
pressure conditions, due to a phenomena known as 'sublimation'.....IOW,

no
"boiling" is needed.

http://www.newton.dep.anl.gov/askasc.../chem03598.htm

--

SVL


Sam,

I think Dido is talking about when you have a evap coil exposed to other
cold temps within a running freezer.. a common occurence in the
commercial world.

This is what the man meant, I believe.


Jake,

Doesn't matter--next time it snows, watch your outside temp real close, and
take note of any period over several days, or perhaps up to a week where the
temp stays constantly below freezing....notice that the snow 'just kinda
dissapears'....given enough time, it will eventually dissapear altogether,
without ever reaching a temp above freezing, and without rain falling on it,
etc.....now note that this process speeds up considerably at pressures below
atmospheric.

--

SVL


This is Turtle.

i see the example all the time with ice cub trays all the time. Fill a ice cube
tray with water and let them freeze real good and then keep them in the freezer
for 1 years. You will come back and find all the ice gone out of the ice cube
tray. I call it freezer evaperation or called freezer burning the ice. This
dehydration takes all the moisture out of food product and is called freezer
burn.


Also it can be freeze dried...

Joseph

TURTLE






  #51   Report Post  
pjm@see_my_sig_for_address.com
 
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On Sun, 21 Aug 2005 14:19:42 -0700, "Joseph"
wrote:


wrote in message
news
On Sun, 21 Aug 2005 10:46:35 -0700, "PrecisionMachinisT"
wrote:


wrote in message
.. .
On Sun, 21 Aug 2005 00:41:04 -0500, Richard J Kinch
wrote:

I am not sure where you live but it is about 600 degrees F warmer than
"space " on earth, even in the winter. There is plenty of available
heat to sublimate water.

Repeat after me: temperature is not heat.

Repeat after me, a gas at a given temperature (ambient air) is heat.

See cat...notice cat has a tail....pull on cat's tail........

Repeat until bored.


See cow.

See cow udders.

Pull cow udders.

Get milk.

If cow only have one udder, get cream.


"I think I'll go wash up..."

I guess that can wait for an udder day.

Shoulda wore gloves.


Click here every day to feed an animal that needs you today !!!

http://www.theanimalrescuesite.com/

Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/
  #52   Report Post  
~^Johnny^~
 
Posts: n/a
Default

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

See cow.

See cow udders.

Pull cow udders.

Get milk.

If cow only have one udder, get cream.


"I think I'll go wash up..."

I guess that can wait for an udder day.

Shoulda wore gloves.


Now you are in for a real teat.


-----BEGIN PGP SIGNATURE-----
Version: PGP 7.1

iQA/AwUBQwj3mAIk7T39FC4ZEQIg+gCeOJleXpVn84fHEmoKKKx74A qePXoAoOL5
YiIqi2zXsbkKjEjvLeO8Cl7g
=zaPo
-----END PGP SIGNATURE-----
--
-john
wide-open at throttle dot info
  #53   Report Post  
PrecisionMachinisT
 
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Default


"~^Johnny^~" wrote in message
...
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

See cow.

See cow udders.

Pull cow udders.

Get milk.

If cow only have one udder, get cream.

"I think I'll go wash up..."

I guess that can wait for an udder day.

Shoulda wore gloves.


Now you are in for a real teat.


Nice tits at this site:

http://www.nice-tits.org/

--

SVL


  #54   Report Post  
 
Posts: n/a
Default

wrote:

Repeat after me, a gas at a given temperature (ambient air) is heat.


Air = heat.
Oxygen = heat.
Nitrogen = heat...

Learn something new every day around here.

Nick

  #56   Report Post  
 
Posts: n/a
Default

wrote:

Repeat after me, a gas at a given temperature (ambient air) is heat.


Air = heat.
Oxygen = heat.
Nitrogen = heat...

Learn something new every day around here.


If that air, nitrogen and oxygen is anything but 0 degrees Kelvin it
has heat. That is why we have "AIR" conditionoing in the first place.


Oh, you meant it CONTAINS heat...

Nick

  #57   Report Post  
DiDo
 
Posts: n/a
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Thank You
Mr. Richard J Kinc
For explaining to some of these VUSIS
and I say to some because when arrogance
superseded the ignorance there are some people
that will not except truth or the facts.
It does not metter how had you may try
Sorry I am not that patient
Good Luck from Dido


"Travis Jordan" wrote in message
.. .
papaya wrote:
if you only pull 500 microns of vacuum for your customer, you are not
getting all of the water out and are going to be making hydrochloric
acid for them, so they can buy a new unit from you, Mr. Con Artist.


Most manufacturers installation instructions say evacuate to 350
microns, then insure that the vacuum holds for at least a minute after
closing off the vacuum pump. Their instructions (and their warranty)
are good enough for me.




  #58   Report Post  
rick1matthews
 
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Richard J Kinchwrote:
PrecisionMachinisT writes:

A lot of people have been taught the pseudo-scientific myth that

"water
boils in a vacuum" in some magic sense that it doesn't in the
atmosphere. The truth is that water vaporizes in a vacuum or in the


atmosphere the same way: *only* because you add heat. In the same
sense, water doesn't boil at 212 deg F, it boils because you add

more
heat after it is at 212 deg F.


Nothing pseudo-scientific about it. I have boiled water with
ice.

Here is how: take a glass flask with an indentation in the bottom, add
a little water. You may want to add boiling chips to make the effect
more gradual. Attach a cork with a rubber hose to the top to vent.

Put it on a bunsen burner and boil, just to get the steam to drive all
the air out. Remove heat and clamp the rubber hose. Let it cool.

Invert, add ice to the depression, and watch the cool water boil, not
with the addition of heat, but with the addition of ice. I have
boiled water down to 60 degrees F with this technique.

What is happening is that cooling the glass on top causes most of the
remaining steam to condense, establishing a decent vacuum. Lowering
the pressure over the water lowers the boiling point, so the water
now boils.

You have said repeatedly that one must add heat for sublimation to
occur. That is not true. Sublimation and evaporation both proceed
by the same mechanism. Pour water on the floor, and it will
evaporate without addition of heat, unless the relative humidity is
100%. Sublimation happens, too, just starting from the solid instead
of liquid phase of water.

What is happening microscopically is related to the the kinetic energy
of the molecules. Temperature is not heat, as you pointed out. But
they are related. Temperature is defined to be proportional to the
random translational kinetic energy per molecule of the material.
Heat transfer is equal to the change of the random translation
kinetic energy plus rotational and vibrational kinetic energy plus
changes in potential energy. So any substance above absolute zero
contains heat, and its molecules have a distribution of kinetic
energies.

When a molecule on the surface achieves an atypically large kinetic
energy from collisions with its neighbors, it reaches escape
velocity. If the substance is a liquid, we call it evaporation. If
it is a solid, we call it sublimation. There is always a reverse
process of capture from the atmosphere. But the process is usually
slower.

The temperature of the surface determines the escape rate. The
partial pressure of water in the surrounding atmosphere determines
the capture rate. In a perfect vacuum, the capture rate is zero, and
the net effect is evaporation or sublimation.

  #59   Report Post  
 
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rick1matthews wrote:

Pour water on the floor, and it will evaporate without addition of heat...


It's more accurate to say that the heat required to evaporate the water
(about 1000 Btu/lb) comes from the surroundings, ie this evaporation
cools the floor, the air, and so on.

Nick

  #60   Report Post  
Rick
 
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Default


"rick1matthews" wrote in
message ...
Richard J Kinchwrote:

PrecisionMachinisT writes:

A lot of people have been taught the pseudo-scientific myth that

"water
boils in a vacuum" in some magic sense that it doesn't in the
atmosphere. The truth is that water vaporizes in a vacuum or in

the

atmosphere the same way: *only* because you add heat. In the same
sense, water doesn't boil at 212 deg F, it boils because you add

more
heat after it is at 212 deg F.


Nothing pseudo-scientific about it. I have boiled water with
ice.

Here is how: take a glass flask with an indentation in the bottom,

add
a little water. You may want to add boiling chips to make the effect
more gradual. Attach a cork with a rubber hose to the top to vent.

Put it on a bunsen burner and boil, just to get the steam to drive

all
the air out. Remove heat and clamp the rubber hose. Let it cool.

Invert, add ice to the depression, and watch the cool water boil,

not
with the addition of heat, but with the addition of ice. I have
boiled water down to 60 degrees F with this technique.

What is happening is that cooling the glass on top causes most of

the
remaining steam to condense, establishing a decent vacuum. Lowering
the pressure over the water lowers the boiling point, so the water
now boils.


Julius Sumner Miller would be proud : )


You have said repeatedly that one must add heat for sublimation to
occur. That is not true. Sublimation and evaporation both proceed
by the same mechanism. Pour water on the floor, and it will
evaporate without addition of heat, unless the relative humidity is
100%. Sublimation happens, too, just starting from the solid

instead
of liquid phase of water.

What is happening microscopically is related to the the kinetic

energy
of the molecules. Temperature is not heat, as you pointed out. But
they are related. Temperature is defined to be proportional to the
random translational kinetic energy per molecule of the material.
Heat transfer is equal to the change of the random translation
kinetic energy plus rotational and vibrational kinetic energy plus
changes in potential energy. So any substance above absolute zero
contains heat, and its molecules have a distribution of kinetic
energies.

When a molecule on the surface achieves an atypically large kinetic
energy from collisions with its neighbors, it reaches escape
velocity. If the substance is a liquid, we call it evaporation. If
it is a solid, we call it sublimation. There is always a reverse
process of capture from the atmosphere. But the process is usually
slower.

The temperature of the surface determines the escape rate. The
partial pressure of water in the surrounding atmosphere determines
the capture rate. In a perfect vacuum, the capture rate is zero,

and
the net effect is evaporation or sublimation.





  #61   Report Post  
Rick Matthews
 
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wrote on 8/25/2005 8:37 AM:
rick1matthews wrote:


Pour water on the floor, and it will evaporate without addition of heat...



It's more accurate to say that the heat required to evaporate the water
(about 1000 Btu/lb) comes from the surroundings, ie this evaporation
cools the floor, the air, and so on.


Some of the heat comes from the surroundings in
this example. Some comes from within the water itself.

Key to this discussion is that no external source of
heat is needed to evaporate water.

Were a 70 degree F drop of water suspended (perhaps in a weightless
environment) in a hard vacuum, which in turn is completely
surrounded by shiny surfaces cooled to 100 milliKelvin, the drop
would still evaporate.

So where did the heat come to evaporate it?

Statements were made earlier that water only boils when
heat is added and that water only evaporates when heat
is added. Neither statement is true.

Water evaporates whenever the partial pressure of water
in the surrounding atmosphere is so small that the
capture of the water molecules from the air is less
than the escape of water molecules from the surface
of the water. The rate of escape is determined by
the water temperature. The rate of capture is determined
by the partial pressure of water. The water temperature
at which the two are in equilibrium is called the dew point.
If the water is cooler than the dew point, you get net
condensation. If the water is warmer than this dew point,
you get net evaporation.

When air pressure is very low, the partial pressure
of water can only be lower. Therefore the dew point must
be quite low, so that 72 degree F water (or 35 degree F
water, for that matter), is warmer that its dew point.
Water molecules are always escaping, and there are few
water molecules in the environment to balance the process.

Hence, the water evaporates.

The cooler it is, the slower it evaporates, but it does
still evaporate. In a perfect vacuum, even a 1 Kelvin ice
cube would eventually sublime way, though not in billion
years.

--
Rick Matthews

  #62   Report Post  
Richard J Kinch
 
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Rick Matthews writes:

Statements were made earlier that water only boils when
heat is added and that water only evaporates when heat
is added. Neither statement is true.


It is true in the sense that the heat content of the water itself can
only evaporate a small portion of it. If you squirted warm water out of
the Space Shuttle in orbit, some would flash to vapor but most of it would
just wind up floating around frozen. The point is simply that vacuum
itself does not evaporate water, it is heat, contrary to the popular
notion.
  #63   Report Post  
Rick
 
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True, most of the water will freeze before evaporating. But
you also said:

It *will not* sublime at all if there is no heat added, even in a perfect vacuum.


which is not true.

The ice will sublime in a perfect vacuum if it is above absolute zero,
as long as there is any ice left.

Change "at all" to "quickly" and I will agree with you.

Rick

  #64   Report Post  
Richard J Kinch
 
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Rick writes:

The ice will sublime in a perfect vacuum if it is above absolute zero,
as long as there is any ice left.


If it is above absolute zero, then it must have had some heat added.
  #65   Report Post  
Richard J Kinch
 
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The thing you are missing is gravity. Ice is not going to "float
around" in that pipe. It will lay on the pipe (compressor, valves etc)
and heat from the ambient air on the other side of the pipe will
evaporate the water.


Some of it will gain heat by this process, although much more slowly
than one might expect or hope. Remember it takes a huge amount of heat
transfer to vaporize water, and the vacuum is an excellent insulator.
Parts of a
glob of water in contact with the system will freeze and then tend to
sublimate a thin layer of vapor to separate themselves from the heat
source, instead of staying in intimate contact. And remember this
doesn't work at all for water entrained in or bound to something else.

Another practical problem in a AC system is that the water may trapped
on the other side of 50 feet of of 3/8 inch tubing from the vacuum
source, such as if the service connection is at the compressor on a
split system with the water stuck up in the evaporator. The back
pressure of a long thin line will spoil the vacuum on the other end.

My point is simply to correct the common misconception among AC techs
that if they pull a good vacuum on a system that it is guaranteed to be
dry, because they believe "water boils in a vacuum" from seeing a high
school science demonstration. The purpose of vacuuming an AC system is
to remove non-condensibles, not to clean out contaminants like water.



  #66   Report Post  
Rick
 
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That does not follow.

Rick

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Default 500 microns? - then you are a HACK!!

Summary judgment God. Glad to know asking means finished. You should run Nasa. You know everything based on one question. And you are polite. Never insulting, never profabe. What a guy
  #68   Report Post  
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Posts: 1
Default 500 microns? - then you are a HACK!!

Well put. Old school gentlemen who is an excellent teacher. I can tell you didnt read that in a book , and if applied and refined. Amen. Like the no name calling, shows confidence. 35 yrs tech., installer, engineer.
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