REFLECTOR:weak gas struts / beating a dead horse dept.
John Dibble
reflector@tvbf.org
Tue, 06 Jan 2004 21:19:41 -0600
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Exactly.
different John
Alex Balic wrote:
>John-
>Are you saying that you can pull indefinitely (movement) on a sealed piston
>as long as you exert 14.7 psi on it?
>I propose that if you have no gas (oil only) otherwise you would have to
>assume a very theoretical sealed piston/cylinder that contains 0 molecules
>of gas) within a sealed piston cylinder - lets say it is a cylinder with no
>head- like a cup- you think that you will be able to pull out a (1 in3)
>piston with 14.7 pounds of force?
>
>-----Original Message-----
>From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
>Behalf Of J P Rourke
>Sent: Friday, January 02, 2004 9:35 AM
>To: reflector@tvbf.org
>Subject: Re: REFLECTOR:weak gas struts / beating a dead horse dept.
>
>
>Chuck, the conclusion that this calculated force would vaporize
>hydraulic fluid is irrelevant for determining the upper bound (even if
>it didn't vaporize, a vacuum can still be formed) - "this vacuum force"
>(of area of the piston x atmsopheric pressure) is exclusive of *any*
>vapor pressure considerations; i.e., it would move even if there were no
>fluid and no vapor pressure to consider at all. So if there is no fluid
>at all, with a1.5" piston at sea level (14.7psia), it will take 25.977
>lbs-force to move it.
>
>Once you have the upper bound established, you can conclude that with
>hydraulic fluid in the chamber, it will take somewhat less force
>(because it will vaporize at some point before an absolute vacuum is
>formed); for water it will require even less force; for ether much less.
>
>BTW, the higher the vapor pressure, the more the substance "wants" to
>vaporize (by any method - sublimiation, evaporation or boiling). So
>ether has a higher vapor pressure. It "wants" very much to vaporize, it
>wouldn't take much pulling force for it to do so. I don't know if
>concrete really has a vapor pressure, but I can tell you it would be
>very very low!
>
>-John
>
>
>
>
>Chuck Jensen wrote:
>
>
>
>>Wow, I knew I should have paid attention in H.S. physics. Your comment is
>>accurate that oil can not be compressed (or water for that matter),
>>
>>
>however,
>
>
>>oil nor water can be "stretched" or expanded until enough force is exerted
>>to exceed the vapor pressure of that material. In other words, water and
>>oil are "solid" both ways until the vacuum is great enough to "boil" the
>>water or oil by reducing vapor pressure. Remember how water boils at a
>>lower temp in Denver than it does in Gainesville, FL (where everyone is
>>boiling over the thumping Iowa gave them...and good riddance).
>>
>>I've seen a number of calcs thrown out about how many pounds of force can
>>
>>
>be
>
>
>>applied given areas of a piston, et all. However, no one has concluded
>>
>>
>that
>
>
>>this vacuum force is anywhere near sufficient to vaporize hydraulic fluid.
>>
>>Finally, going back to the syringe example, yes, if you pull on it, it will
>>come out, but that is a function of the lousy seal in the syringe, low
>>
>>
>vapor
>
>
>>pressure of water, likelihood that there was a small amount of air still in
>>the syringe and/or liquid in syringe contained some dissolved gas which
>>
>>
>came
>
>
>>out of solution with a small tug.
>>
>>It is still correct that if you take a hydraulically locked system (no air,
>>no water or gas contamination, no seal leakage), that the plunger will NOT
>>move until you pull with a very large force; one great enough to vaporize
>>the hydraulic fluid. Given that the vapor pressure of hydraulic fluid is
>>very close to a perfect vacuum, it will take very large, even massive,
>>mechanical force to form a bubble.
>>
>>I'm pretty sure this is all true, but then, I didn't think they'd find
>>Saddam in a spider hole either.
>>
>>Chuck Jensen
>>
>>
>>-----Original Message-----
>>From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
>>Behalf Of Dave Black
>>Sent: Friday, January 02, 2004 5:46 AM
>>To: reflector@tvbf.org
>>Subject: REFLECTOR:weak gas struts / beating a dead horse dept.
>>
>>
>>
>>
>>
>>
>>>Al,
>>>
>>>
>>>
>>>
>>
>>
>>
>>>Well; it may be a hard mental concept, but, of course, it will
>>>move.
>>>
>>>
>>>
>>>
>>You are absolutely correct. I've done it many times with a hypodermic
>>syringe.
>>
>>But I can understand why some might believe movement of the piston/plunger
>>impossible. Until you pull with force equal to atmospheric pressure times
>>area
>>of the piston, no piston movement whatsoever occurs. This can give the
>>impression that it's not going to move no matter hard you pull. However,
>>once
>>you overcome the force of atmospheric pressure (and create a vacuum),
>>movement
>>will occur with little additional effort.
>>
>>That's because vacuum is simply zero air pressure. It's impossible to suck
>>
>>
>a
>
>
>>vacuum below zero pressure. If you have a piston with an area of 1 square
>>inch, with zero pressure on one side of the piston and 15psi (sea level
>>pressure) on the other, you'll need 15 pounds of force to move the piston
>>off
>>its stop.
>>
>>It's exactly the same as if you were lifting a 15 pound dumbbell off the
>>floor. 5 pounds of lifting force wouldn't budge it. Nor would 14. It's
>>
>>
>still
>
>
>>on the floor. But once you lift with 15 pounds of force it begins to move.
>>Apply 16 pounds, and it'll move upward fairly quickly.
>>
>>Don't be confused by the oil. Unless the oil in this hypothetical hydraulic
>>system has some glue properties, the most it can 'suck' is 15psi. Beyond
>>that,
>>the piston's going to move.
>>
>>Note that all of this pertains to closing off the intake port on the
>>
>>
>suction
>
>
>>side of the piston. The pressure side is a whole different matter. You
>>cannot
>>compress a fluid, so closing off the exit port would absolutely stop the
>>piston. Until something breaks.
>>
>>Dave Black
>>_______________________________________________
>>To change your email address, visit
>>http://www.tvbf.org/mailman/listinfo/reflector
>>
>>Visit the gallery! www.tvbf.org/gallery
>>user:pw = tvbf:jamaicangoose
>>Check new archives: www.tvbf.org/pipermail
>>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>
>>_______________________________________________
>>To change your email address, visit
>>
>>
>http://www.tvbf.org/mailman/listinfo/reflector
>
>
>>Visit the gallery! www.tvbf.org/gallery
>>user:pw = tvbf:jamaicangoose
>>Check new archives: www.tvbf.org/pipermail
>>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>
>>
>>
>>
>>
>>
>
>
>
>_______________________________________________
>To change your email address, visit
>http://www.tvbf.org/mailman/listinfo/reflector
>
>Visit the gallery! www.tvbf.org/gallery
>user:pw = tvbf:jamaicangoose
>Check new archives: www.tvbf.org/pipermail
>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>
>_______________________________________________
>To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>
>Visit the gallery! www.tvbf.org/gallery
>user:pw = tvbf:jamaicangoose
>Check new archives: www.tvbf.org/pipermail
>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>
>
>
>
>
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Exactly.<br>
different John<br>
<br>
Alex Balic wrote:<br>
<blockquote type="cite"
cite="midNMBBLLIAALMFAOKJBKPDMEINCNAA.alex157@direcway.com">
<pre wrap="">John-
Are you saying that you can pull indefinitely (movement) on a sealed piston
as long as you exert 14.7 psi on it?
I propose that if you have no gas (oil only) otherwise you would have to
assume a very theoretical sealed piston/cylinder that contains 0 molecules
of gas) within a sealed piston cylinder - lets say it is a cylinder with no
head- like a cup- you think that you will be able to pull out a (1 in3)
piston with 14.7 pounds of force?
-----Original Message-----
From: <a class="moz-txt-link-abbreviated" href="mailto:reflector-admin@tvbf.org">reflector-admin@tvbf.org</a> [<a class="moz-txt-link-freetext" href="mailto:reflector-admin@tvbf.org">mailto:reflector-admin@tvbf.org</a>]On
Behalf Of J P Rourke
Sent: Friday, January 02, 2004 9:35 AM
To: <a class="moz-txt-link-abbreviated" href="mailto:reflector@tvbf.org">reflector@tvbf.org</a>
Subject: Re: REFLECTOR:weak gas struts / beating a dead horse dept.
Chuck, the conclusion that this calculated force would vaporize
hydraulic fluid is irrelevant for determining the upper bound (even if
it didn't vaporize, a vacuum can still be formed) - "this vacuum force"
(of area of the piston x atmsopheric pressure) is exclusive of *any*
vapor pressure considerations; i.e., it would move even if there were no
fluid and no vapor pressure to consider at all. So if there is no fluid
at all, with a1.5" piston at sea level (14.7psia), it will take 25.977
lbs-force to move it.
Once you have the upper bound established, you can conclude that with
hydraulic fluid in the chamber, it will take somewhat less force
(because it will vaporize at some point before an absolute vacuum is
formed); for water it will require even less force; for ether much less.
BTW, the higher the vapor pressure, the more the substance "wants" to
vaporize (by any method - sublimiation, evaporation or boiling). So
ether has a higher vapor pressure. It "wants" very much to vaporize, it
wouldn't take much pulling force for it to do so. I don't know if
concrete really has a vapor pressure, but I can tell you it would be
very very low!
-John
Chuck Jensen wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Wow, I knew I should have paid attention in H.S. physics. Your comment is
accurate that oil can not be compressed (or water for that matter),
</pre>
</blockquote>
<pre wrap=""><!---->however,
</pre>
<blockquote type="cite">
<pre wrap="">oil nor water can be "stretched" or expanded until enough force is exerted
to exceed the vapor pressure of that material. In other words, water and
oil are "solid" both ways until the vacuum is great enough to "boil" the
water or oil by reducing vapor pressure. Remember how water boils at a
lower temp in Denver than it does in Gainesville, FL (where everyone is
boiling over the thumping Iowa gave them...and good riddance).
I've seen a number of calcs thrown out about how many pounds of force can
</pre>
</blockquote>
<pre wrap=""><!---->be
</pre>
<blockquote type="cite">
<pre wrap="">applied given areas of a piston, et all. However, no one has concluded
</pre>
</blockquote>
<pre wrap=""><!---->that
</pre>
<blockquote type="cite">
<pre wrap="">this vacuum force is anywhere near sufficient to vaporize hydraulic fluid.
Finally, going back to the syringe example, yes, if you pull on it, it will
come out, but that is a function of the lousy seal in the syringe, low
</pre>
</blockquote>
<pre wrap=""><!---->vapor
</pre>
<blockquote type="cite">
<pre wrap="">pressure of water, likelihood that there was a small amount of air still in
the syringe and/or liquid in syringe contained some dissolved gas which
</pre>
</blockquote>
<pre wrap=""><!---->came
</pre>
<blockquote type="cite">
<pre wrap="">out of solution with a small tug.
It is still correct that if you take a hydraulically locked system (no air,
no water or gas contamination, no seal leakage), that the plunger will NOT
move until you pull with a very large force; one great enough to vaporize
the hydraulic fluid. Given that the vapor pressure of hydraulic fluid is
very close to a perfect vacuum, it will take very large, even massive,
mechanical force to form a bubble.
I'm pretty sure this is all true, but then, I didn't think they'd find
Saddam in a spider hole either.
Chuck Jensen
-----Original Message-----
From: <a class="moz-txt-link-abbreviated" href="mailto:reflector-admin@tvbf.org">reflector-admin@tvbf.org</a> [<a class="moz-txt-link-freetext" href="mailto:reflector-admin@tvbf.org">mailto:reflector-admin@tvbf.org</a>]On
Behalf Of Dave Black
Sent: Friday, January 02, 2004 5:46 AM
To: <a class="moz-txt-link-abbreviated" href="mailto:reflector@tvbf.org">reflector@tvbf.org</a>
Subject: REFLECTOR:weak gas struts / beating a dead horse dept.
</pre>
<blockquote type="cite">
<pre wrap="">Al,
</pre>
</blockquote>
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">Well; it may be a hard mental concept, but, of course, it will
move.
</pre>
</blockquote>
<pre wrap="">You are absolutely correct. I've done it many times with a hypodermic
syringe.
But I can understand why some might believe movement of the piston/plunger
impossible. Until you pull with force equal to atmospheric pressure times
area
of the piston, no piston movement whatsoever occurs. This can give the
impression that it's not going to move no matter hard you pull. However,
once
you overcome the force of atmospheric pressure (and create a vacuum),
movement
will occur with little additional effort.
That's because vacuum is simply zero air pressure. It's impossible to suck
</pre>
</blockquote>
<pre wrap=""><!---->a
</pre>
<blockquote type="cite">
<pre wrap="">vacuum below zero pressure. If you have a piston with an area of 1 square
inch, with zero pressure on one side of the piston and 15psi (sea level
pressure) on the other, you'll need 15 pounds of force to move the piston
off
its stop.
It's exactly the same as if you were lifting a 15 pound dumbbell off the
floor. 5 pounds of lifting force wouldn't budge it. Nor would 14. It's
</pre>
</blockquote>
<pre wrap=""><!---->still
</pre>
<blockquote type="cite">
<pre wrap="">on the floor. But once you lift with 15 pounds of force it begins to move.
Apply 16 pounds, and it'll move upward fairly quickly.
Don't be confused by the oil. Unless the oil in this hypothetical hydraulic
system has some glue properties, the most it can 'suck' is 15psi. Beyond
that,
the piston's going to move.
Note that all of this pertains to closing off the intake port on the
</pre>
</blockquote>
<pre wrap=""><!---->suction
</pre>
<blockquote type="cite">
<pre wrap="">side of the piston. The pressure side is a whole different matter. You
cannot
compress a fluid, so closing off the exit port would absolutely stop the
piston. Until something breaks.
Dave Black
_______________________________________________
To change your email address, visit
<a class="moz-txt-link-freetext" href="http://www.tvbf.org/mailman/listinfo/reflector">http://www.tvbf.org/mailman/listinfo/reflector</a>
Visit the gallery! <a class="moz-txt-link-abbreviated" href="http://www.tvbf.org/gallery">www.tvbf.org/gallery</a>
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Check new archives: <a class="moz-txt-link-abbreviated" href="http://www.tvbf.org/pipermail">www.tvbf.org/pipermail</a>
Check old archives: <a class="moz-txt-link-freetext" href="http://www.tvbf.org/archives/velocity/maillist.html">http://www.tvbf.org/archives/velocity/maillist.html</a>
_______________________________________________
To change your email address, visit
</pre>
</blockquote>
<pre wrap=""><!----><a class="moz-txt-link-freetext" href="http://www.tvbf.org/mailman/listinfo/reflector">http://www.tvbf.org/mailman/listinfo/reflector</a>
</pre>
<blockquote type="cite">
<pre wrap="">Visit the gallery! <a class="moz-txt-link-abbreviated" href="http://www.tvbf.org/gallery">www.tvbf.org/gallery</a>
user:pw = tvbf:jamaicangoose
Check new archives: <a class="moz-txt-link-abbreviated" href="http://www.tvbf.org/pipermail">www.tvbf.org/pipermail</a>
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</pre>
</blockquote>
<pre wrap=""><!---->
_______________________________________________
To change your email address, visit
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