REFLECTOR:RE:weak gas struts

[Chuck Jensen]

Well, the syringe example was not exactly what I was inquiring about, though
its certainly illustrative of how a vacuum is formed.  My question was given
the very high (or is it low, I always confuse the two) vapor pressure of
oil, it's going to take a very high vacuum to form a bubble.  Is the "pull"
on the plunger sufficient to cause the hydraulic oil to cavitate?

Isn't this the reason we use hydraulic oils and brake fluids...for their
very high vapor pressure.  When brake fluid gets contaminated with water,
the hot brakes will heat the water/brake fluid to +212F which will result in
water boiling off which is just another way of saying its vapor pressure was
exceeded?  Richard, there may well be a bubble form but it just seems it
would take a very robust vacuum to vaporize the oil.

Of course, there is an unrelated but coincident reaction that often occurs
when needing to brake sufficiently hard so as to vaporize the water in the
contaminated brake fluid; namely, sweat formation on the brow.

Chuck Jensen


-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of Richard@Riley.net
Sent: Thursday, January 01, 2004 6:03 PM
To: reflector@tvbf.org
Subject: RE: REFLECTOR:RE:weak gas struts


If you pull hard enough, even if the vapor pressure was zero, it would move.

Simple experiment.  Take a syringe, no needle.  Plug the end with your 
thumb.  Pull out the plunger.  It takes some force, probably 1-5 lb or so 
(depending on the diameter of the plunger) but it WILL pull.  Inside is a 
near vacuum.  Let go and it will snap in.  The vapor pressure of your thumb 
isn't significant.

The force you have to apply is the area of the face of the plunger times 
one atmosphere.  If the plunger is 1/2" in diameter, that force is 2.88 lbs.

If there is vapor pressure in the working fluid, the force is the area 
times the atmospheric pressure minus vapor pressure.




At 06:36 PM 1/1/04 -0500, Chuck Jensen wrote:
>Are you sure hydraulic will form a bubble under vacuum (likely to be
>encountered in this instance) given the vapor pressure of the hydraulic
>fluid compared to water?
>
>Chuck Jensen
>
>
>-----Original Message-----
>From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
>Behalf Of steve korney
>Sent: Sunday, December 28, 2003 1:21 AM
>To: reflector@tvbf.org
>Subject: RE: REFLECTOR:RE:weak gas struts
>
>
>It's like cavitations...That's how a boat propeller makes bubbles under
>water...
>
>
>Best... Steve
>
>
>---------------------------------------------------------------------------
-
>-------------------------------
>
>
>Steve,
>How does it produce this bubble? In my experience, you can lock a hydraulic
>cylinder from either side by blocking either the intake or exhaust port.
>
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